Population ecology of the Three-toed Woodpecker under varying food supplies by Philippe Fayt
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University of Joensuu, PhD Dissertations in Biology
No:21
Population ecology
of the Three-toed Woodpecker
under varying food supplies
by
Philippe Fayt
Joensuu
2003The ancient Forest. All that lives here, lives not next to each other, but rather with each other. In
this community everything submits to influence, and imposes its influence on the environment. A
splendid, harmonised symphony of power, health and immortality.
Jan Walencik (2000)
Front cover drawing:
The star of the book (© Philippe Fayt)Fayt, Philippe Population ecology of the Three-toed Woodpecker under varying food supplies. – University of Joensuu, 2003, 126 pp. University of Joensuu, PhD Dissertations in Biology, n:o X. ISSN 1457-2486 ISBN 952-458-384-4 Keywords: Breeding density, body size, brood size, heterogeneity, Fennoscandia, food supply, natal dispersal, Picoides tridactylus, parental care, population dynamics, predatory impact, resource phenology, scale In this study, ecological factors underlying multi-scale variability in the productivity and abundance of the Three-toed Woodpecker Picoides tridactylus were studied in Fennoscandia from 1996-1999. Patch suitability for a resident woodpecker was estimated in relation to seasonal and inter-annual changes in prey availability and profitability. The methods used to clarify dietary preferences and sample prey populations included bark sampling and insect trapping with window-flight traps. The information on dispersal patterns comes from ringing data records. The results suggest that food supply, determined by the annual timing of prey development and prey abundance, and its variability in time and space are key factors in understanding individual responses and population processes in the woodpecker. In agreement with previous studies of factors limiting forest bird populations, I found the woodpecker breeding density and success to depend on different food resources. While annual variation in breeding density paralleled variation in the bird’s autumn-winter food supply, the spruce bark beetles (Col., Scolytidae), brood size was related to the amount of profitable longhorn beetle larvae (Col., Cerambycidae), the nestling’s main food. Different patterns of annual changes in the abundance of the woodpecker’s autumn-winter and summer food supply between burnt and old-growth patches emphasised the importance of patch disturbance history for its suitability as a woodpecker habitat. The management level of a forest landscape was found to influence the spatial distribution of bark beetle species diversity and abundance within its inclusive old-growth habitat units, depending on whether a patch was surrounded by ditched clear-cuts or untouched peatlands. In particular, with a lower spruce bark beetle abundance at the edges of old forest remnants in drained managed landscapes compared to patches in swampy environment, my results provide explanation for the importance of swamp forests for the woodpecker winter survival and subsequent breeding density. In Finland, juvenile woodpeckers dispersed from their natal habitats at times of sudden changes in the spatial distribution of insect prey as part of their development, leading to a local decline in prey availability. The results suggest that prey availability, whose timing is mediated by the timing of prey development, has a proximate effect on the propensity of the juveniles to disperse, although a causal relationship was not found. Although a speculative conclusion, annual trends in natal dispersal rate in relation to spring temperature incline me to propose that the yearly number of dispersers from a population depends on its productivity, which, in turn, depends on how closely reproducing individuals are able to match breeding time with annual pattern of food supply. The importance of the juveniles for the population dynamics of conifer bark beetles is acknowledged, depending on the numbers of woodpeckers dispersing over the landscape when beetle larvae reach a profitable size. The possibility that the juveniles might disperse at different times from regions with contrasting temperature conditions is discussed, as a result of spatial heterogeneity in resource phenology. Philippe Fayt, Department of Biology, University of Joensuu, P.O. Box 111, FIN-80101 Joensuu, Finland
CONTENTS
LIST OF ORIGINAL PUBLICATIONS
1. INTRODUCTION 9
2. THE STUDY 10
2.1. Aims 10
2.2. Predictions 11
2.3. Why? 11
3. MATERIAL AND METHODS 12
3.1. Study species 12
3.2. Study areas 14
3.3. General methods 14
3.3.1. The woodpecker data 14
3.3.1.1. Reproduction 15
3.3.1.2. Dispersal patterns 15
3.3.2. The insect prey data 16
3.3.2.1. Prey abundance 16
3.3.2.2. Prey profitability 17
4. RESULTS AND DISCUSSION 17
4.1. Diet preferences 17
4.2. Breeding density 18
4.3. Breeding performance 18
4.4. Parental care 20
4.5. Natal dispersal 20
4.6. Body size and dispersal patterns 21
4.7. Predatory impact 22
4.8. Habitat suitability 23
5. CONCLUDING REMARKS 24
5.1. Food supply and population ecology 24
5.2. Management implications 25
ACKNOWLEDGEMENTS 28
REFERENCES 29LIST OF ORIGINAL PUBLICATIONS
This thesis is based on the following articles, referred to in the text by their Roman numerals
I-VII:
I Fayt, P. 1999. Available insect prey in bark patches selected by the Three-toed
Woodpecker Picoides tridactylus prior to reproduction. Ornis Fennica 76: 135-140.
II Fayt, P. 2003. Time of natal dispersal and reproductive decisions of the Three-toed
Woodpecker under varying food conditions. – In: Pechacek, P. and d’Oleire-
Oltmanns, W. (eds.), International Woodpecker Symposium. Forschungsbericht 48.
Nationalparkverwaltung Berchtesgaden, pp. 35-48.
III Fayt, P. Brood size determinants of the Three-toed Woodpecker Picoides tridactylus in
boreal forests. Manuscript (submitted).
IV Fayt, P. Dispersal patterns of Three-toed Woodpeckers in relation to food availability:
consequences for the population dynamics of the woodpecker at the scale of
Fennoscandia. Manuscript.
V Fayt, P., Machmer, M.M. and Steeger, C. Regulation of conifer bark beetles by
woodpeckers - a literature review. Manuscript (submitted).
VI Fayt, P. 2003. Insect population changes in habitats with declining vs. stable Three-
toed Woodpecker populations. Ornis Fennica 80 (in press).
VII Fayt, P. 2003. Old-growth boreal forests, three-toed woodpeckers and saproxylic
beetles – the importance of landscape management history on local consumer-resource
dynamics. Ecological Bulletins 51 (in press).
Some unpublished results are also presented.1. INTRODUCTION outcome of social interactions within and
between species (Henderson and Hart
Understanding of the factors limiting bird 1995, Sutherland 1996). Partially reduced
populations has always been a challenging food supplies explain interference between
and exciting field of interest among foraging individuals (Dolman 1995,
population biologists. Its difficulty arises Cresswell 1998), which promotes the
from the multiplicity of factors and scales dispersal of juveniles as a result of
that influence the key parameters of adjustments in dominance hierarchies
population dynamics: survival, dispersal, (Lundberg 1985, Hannon et al. 1987).
and reproduction. Its implications are Food supply influences indirectly the
crucial, since only a thorough predation rate, for example at nest sites,
understanding of variability in individual depending on alternative prey availability,
numbers is likely to provide meaningful the landscape context and the predator
guidelines for population management community (Schmiegelow and Mönkkönen
(Marzluff et al. 2000). 2002). Food level and general habitat
Main factors related to changes in bird quality also affects the magnitude of
numbers and distribution include food- critical trade-offs in birds, for example
supply, inter- and intra-specific between reproductive effort and health
competition, predation, and parasitism condition (Wiehn 1997), mate choice
(Newton 1998). Among these, food has an (Alatalo et al. 1986), parental care
overwhelming influence on the major life (Hakkarainen and Korpimäki 1994) and
history traits of individuals and population the evolution of reproductive strategies
processes, and it controls directly or (e.g., Korpimäki 1988).
indirectly the effects of other factors As a general pattern, food is a
(Newton 1980, Martin 1987). For example, fluctuating resource, changing in space and
it has been shown that food availability in time in a predictable or unpredictable way
autumn and winter-time determines local (Dempster and Pollard 1981). In the
variations in subsequent breeding density Northern Hemisphere, food supply
by influencing the survival and recruitment changes annually in parallel to predictable
of juveniles into populations (Perrins 1966, variation in photoperiod and ambient
Van Balen 1980, Hannon et al. 1987, temperature. The most spectacular
Nilsson 1987). In spring, food supply consequence of this is probably the
affects laying date and thereby clutch size evolution of bird migration over continents
in those species in which there is a (Gauthreaux 1985). Nevertheless, on
seasonal decline in clutch size, as smaller spatial scales, variation in food
demonstrated by food supplementation distribution, quality, abundance, and
experiments (Martin 1987, Daan et al. profitability is also a reality, although not
1988). Laying time, in turn, determines as obvious.
fledging success (Smith 1993, Verboven Heterogeneity is a natural and multi-
and Visser 1998), and environmental scale feature of forested habitats
conditions experienced during ontogeny (Kuuluvainen 2002). It involves the fact
affect fitness-related traits such as clutch that forest habitats are spatially variable in
size (Haywood and Perrins 1992) and body terms of resources available for a living
size (Sedinger et al. 1995) of the surviving bird, whether heterogeneity is viewed at
individuals. In migrating species, the pre- branch, tree, or stand level. For instance, it
breeding nutritional condition of the is now well established that the nutritional
parents affects reproductive success properties of host plants may differ
(Sandberg and Moore 1996). Spatial tremendously among and within tree
distribution and abundance of food species (Tikkanen 2000). This has direct
resources, on the other hand, influence the implications for the fitness, abundance,
9and population dynamics of herbivorous population processes to habitat
insects but also of their associated heterogeneity at local level, but also on
predators, parasites, and pathogens (Van larger scales.
Balen 1973, Sipura 1999). Similarly,
lichen mass show a strong positive 2. THE STUDY
relationship to mass, diameter and age of
branches (Esseen et al. 1996). Lichen 2.1. Aims
abundance, on the other hand, determines
the number and biomass of invertebrates In this thesis, my aim is to study the
and spiders, which in turn make up the ecological factors underlying variability in
main food source of numerous foliage the seasonal and inter-annual abundance of
gleaning passerine birds (Pettersson et al. the Three-toed Woodpecker Picoides
1995, Pettersson 1996). Below ground tridactylus at patch, landscape, and
level, heterogeneity in soil properties may regional levels in Fennoscandia. More
also contribute to forest structure, for specifically, I investigate whether (1) food
example by predisposing trees to pathogen supply, in terms of both availability and
infestations on root tips, subsequent beetle profitability, determines the breeding
attacks and early mortality (Hertert et al. density, reproductive output, population
1975, Fraedrich and Tainter 1989). dynamics, and predatory impact of the
Although such tree-scale biotic woodpecker (I-V), and (2) how patch and
interactions (so called bottom-up control; landscape silvicultural history may
Lertzman and Fall 1998) are clearly seen influence the outcome of the predator-prey
as a source of multi-scale ecological relationships (VI-VII). The information is
patterns, forest structural features are, then combined to develop forest
however, also to a large extent determined management guidelines that take into
by factors operating and interacting on account the preservation of the species.
larger scales, namely abiotic First (I), I clarify the diet preferences of
environmental and allogenic disturbances the bird prior to reproduction, after taking
(or top-down control) (Kuuluvainen 2002). bark samples from recent foraging trees.
Landscape charateristics such as Then (II, III, IV), I relate seasonal and
topography, soil, hydrology, climate, or inter-annual variation in prey development
land use determine the composition and timing and availability among patches to
physiognomy (i.e., the spatial the reproductive output and dispersal
arrangement) of its inclusive habitat patterns of the woodpecker. In particular, I
patches (Dunning et al. 1992). Variation in test for the hypothesis that prey life cycle
the structure and abiotic conditions of induces changes in food profitability,
forest landscapes, for their part, set the which, together with prey abundance,
limits of microclimatic variability among serves as a predictable cue for assessing
patches and determine their likelihood of the benefits of investment in reproduction,
being disturbed at regular intervals by and explains the onset of the woodpecker’s
physical agents. The importance of multi- natal dispersal. In the next paper (V), a
scale interactions in determining forest literature review allows me to test for the
structure is furthermore emphasised by the idea that predatory woodpeckers, and
possibility of disturbance propagation and especially Three-toed Woodpeckers, can
amplification from tree to landscape levels, contribute to the natural regulation of their
for example during insect outbreaks prey. In the sixth paper (VI), I compare the
(Rykiel et al. 1988). Thus, when studying short-term effects of fire vs. gap-dynamics
various effects of food supply on forest on woodpecker abundance and its food
bird populations, careful attention should supply. Finally (VII), I study whether the
be paid to relating individual responses and conservation value of forest patches for a
10resident woodpecker is landscape specific 5. Local prey availability should decline
by relating prey distribution to edge at the time when young woodpeckers
proximity in old-growth patches with disperse across landscapes.
natural (unditched peatland) vs. managed 6. Earlier-dispersing juveniles should be
(ditched clear-cuts) surroundings. larger than later-dispersing birds, as a
The thesis is based on circumstantial result of higher food supply availability
evidence that food availability limits among early broods.
woodpecker numbers, leading to testable 7. Juvenile woodpeckers should
hypotheses. The available evidence falls disperse first from warmer areas.
into two categories: (a) patch differences in 8. The Three-toed Woodpecker should
food correlated with patch differences in have a stabilising effect on the population
bird numbers (II, III, V); and (b) seasonal dynamics of its prey.
and annual differences in food correlated
with seasonal and annual differences in 2.3. Why?
bird numbers (II, IV, VI). For
convenience, in this study, a patch is There are multiple reasons for choosing the
defined as a focal unit of a forest landscape Three-toed Woodpecker as a study species
that is set off from surrounding habitats by and woodpeckers in general as a group of
an ecologically meaningful edge (Fagan et interest.
al. 1999). Prey availability is an attribute 1. The year-round diet preferences of
of the habitat and refers to the absolute the species are well known, and sampling
amount of food available to a foraging of the insect prey is relatively easy. This
woodpecker. Prey profitability takes into allows for testing hypotheses relative to the
account the temperature-dependent timing importance of food supply on bird
of prey development in relation to the population dynamics.
woodpecker breeding cycle. 2. The Three-toed Woodpecker is a prey
specialist, depending the whole year round
2.2. Predictions on insect preys that colonise dying and
recently dead trees. This makes the
On the basis of the literature, sets of woodpecker a species particularly sensitive
predictions are generated across the to forest management and the consequent
different papers, linking food supply to removal of dead trees. Accordingly, the
woodpecker individual and population Three-toed Woodpecker is a declining
responses. These predictions can be species over most of its range, in parallel
summarised as follows: to fragmentation and loss of naturally
1. The autumn-winter food supply dynamic forest habitats (Rassi 2000). In
should control woodpecker breeding Finland, the Three-toed Woodpecker is
density. included in the list of the Wild Birds
2. Both the availability and profitability Directive of the European Union (i.e., a list
of nestling food supply should explain of species for which every effort should be
breeding time and thereby brood size made to avoid reducing their population
among reproducing individuals. size or range due to human-related
3. Mean brood size should be larger in activities). It is also classified as a Finnish
years with a warmer spring if laying date is responsibility species of European
related to the time of prey development. Conservation Concern, since >10% of its
4. The reproductive output of a European population breeds in the country
population should determine the number of (Rajasärkkä 1997). Yet, although the
dispersing juveniles. negative impact of forest management
practices on saproxylic invertebrate
communities has been increasingly studied
11(Siitonen 2001), its potential cascading Woodpecker has a reduced hallux instead
effects on the reproduction, survival and of a distinct fourth zygodactyl toe as in
recruitment of predatory woodpeckers are Dendrocopos species. Typically, it inhabits
poorly understood. mature boreal or montane coniferous
3. Because of its highly specialised forests, with a distribution that coincides
requirements for properties characterising with that of spruce tree species Picea spp.
naturally dynamic forest patches and (Baldwin 1968, Bock and Bock 1974). In
landscapes, the Three-toed Woodpecker is the whole Eurasian region, the total
an appropriate indicator of forest habitat number of subspecies is five (P. t. albidior,
quality (Angelstam 1998, Nilsson et al. alpinus, crissoleucus, funebris,
2001). In addition, the role of woodpeckers tridactylus). In Europe, the Three-toed
in general as umbrella species and key Woodpecker population is subdivided into
actors in forest animal communities by two subspecies. While the nominal form P.
providing cavities for secondary cavity- t. tridactylus is limited to the boreal forest
nesters is increasingly acknowledged of Fennoscandia and Western Russia, the
(Martikainen et al. 1998, Martin and Eadie sub-species P. t. alpinus is found in the
1999, Mikusinski et al. 2001). mountainous areas of Central, Eastern and
4. From a behavioural perspective, South-East Europe, mainly the Czech
woodpeckers share unique features among Republic, France, Germany, Greece,
birds. In contrast to most altricial bird Poland, Slovakia, and Switzerland
species, the males generally take a larger (Winkler et al. 1995). In North America,
share in parental care than the females three different subspecies are described,
(Winkler et al. 1995). Besides their namely P. t. bacatus, P. t. dorsalis, and P.
peculiar habits of excavating cavities both t. fasciatus. Based the supposition on
for reproduction and for roosting, the mitochondrial gene tree from world-wide
males incubate and brood by night and part the representatives of the genus, the New
of the day, which seems to preclude multi- World Picoides may have evolved from
nest polygynous mating and under some several Eurasian invasions (Weibel and
circumstances promote the rare multi-nest Moore 2002).
polyandry (Willimont et al. 1991, The Three-toed Woodpecker is
Wiktander et al. 2000). Additional everywhere a rare species (Goggans et al.
observations of co-operative breeding in 1989, Tucker and Heath 1994). Occasional
some of the species confirm the adaptive observations of local aggregations in forest
and puzzling nature of their sex-specific areas recently disturbed by fire (Sorvari
reproductive strategies (Stacey and Bock 1994, Murphy and Lehnhausen 1998,
1978, Stacey and Koenig 1984). Imbeau et al. 1999), water (Yeager 1955),
wind (Virkkala et al. 1991), and/or infested
3. MATERIAL AND METHODS by phytophagous insects (Baldwin 1960,
Koplin 1972, Crockett and Hansley 1978)
3.1. Study species suggest that its population size is limited
by habitat/food resources hardly found
The Three-toed Woodpecker is the only under conventional forest management
woodpecker to be found in both the Old (Imbeau et al. 1999). Accordingly, results
and New Worlds (Winkler et al. 1995) from analyses of stomach contents show
(although recent molecular investigations that they prey the whole year round on
suggest that a separate species exists on insects that colonise dying and recently
each continent; Zink et al. 2002). As its dead trees (i.e., with firm bark coverage).
name suggests, and together with the north From late summer to early spring, they
american Black-backed Woodpecker prey almost exclusively on conifer bark
Picoides arcticus, the Three-toed beetles (Coleoptera, Scolytidae), with a
12marked preferences for the species that In this study carried out in Finland, clutch
colonise spruce trees (Hutchison 1951, size varied between 2 and 5 eggs (3.35 ±
Dement’ev 1966, Hogstad 1970, Koplin 0.94, n = 26). The fledglings leave the nest
and Baldwin 1970, Koplin 1972, Massey in June-July; they start to disperse from
and Wygant 1973, Pechacek and Krištín their natal habitats mainly from August to
1993). Three-toed woodpeckers, on the November (Fig. 1). Like most
other hand, have been shown to ignore woodpeckers, the Three-toed Woodpecker
very small spruce bark beetle larvae, is primarily a resident species throughout
younger than 31/2 to 4 months of age its breeding range (Burdett and Niemi
(Koplin and Baldwin 1970). During the 2002). Nevertheless, evidence for large-
summer months, however, wood-boring scale irruptions exist on both continents
beetle larvae, and especially longhorn (Yunick 1985; Fig. 2). As is the case for
beetle larvae (Coleoptera, Cerambycidae), other irruptive bird species, the majority of
contribute significantly to the diet of the dispersing individuals are juveniles
individuals, including nestlings (e.g., Perrins 1966, Hildén 1982; Fig. 2).
(Dement’ev 1966, Hogstad 1970, Pechacek
and Krištín 1996, P. Pechacek and A.
juvenile (1 calendar year old)
Krištín, pers. comm.). Such a seasonal 4
adult (> 1 cy)
variation in diet preferences coincides with
Finland
seasonal changes in habitat use for prey 3
searching. While wintering individuals
preferentially forage in pure spruce stands,
2
No. of dispersing individuals
late spring-summer birds select stands with
a larger deciduous component and forage
on more decayed trees (Wesolowski & 1
Tomialojc 1986, Hogstad 1991, Pechacek
and Krištín 1996, D. Nowak, pers. comm.). 0
The Three-toed Woodpecker starts 4
reproducing the first year following birth
(i.e., in its second calendar year) (P. Fayt, Sweden
3
pers. obs.). It lays between 2 and 6 eggs in
May-June in a newly excavated cavity
(Dement’ev 1966, Wesolowski and 2
Tomialojc 1986).
1
60
No. of captures
0
40 Finland 1970 1975 1980 1985 1990 1995 2000
Sweden
Period
20 Figure 2. Number of juveniles and adults
dispersing in Finland and Sweden (1973-
2000). The annual number of dispersers
0
Aug. Sep. Oct. Nov. Dec. Jan. Feb. was related to the total number of fully-
Period
grown birds ringed each year in each
country and expressed as the number of
Figure 1. Natal dispersal period of the woodpeckers per 10,000 birds ringed.
Three-toed Woodpecker in Finland and
Sweden (1973-2000). The woodpecker’s main insect prey (the
bark beetles and longhorn beetles) share
13similar life-histories: they both attack Monochamus sp.) borers, spend a part of
recently dead trees, they both benefit from their larval stage inside the sapwood
thick, moist phloem (a thin layer of living (xylem) after a first period spent in the
tree tissue found between the outer bark phloem (Post 1984, Bílý and Mehl 1989).
and sapwood), and they both emerge as Such wood-boring activity of larvae into
adults from brood trees for only a brief the sapwood prior to pupation does not
period (Powell 2000). Bark and wood- begin before late August-September of the
boring beetles undergo complete beetle's first season (Rose 1957, Post 1984,
metamorphosis, developing successively Bílý and Mehl 1989).
into larvae (an early soft-bodied form During this study, the main difficulties
without wing pads), pupae (a quiescent encountered in the field were: (1) the rarity
soft form with wing pads), and adults of the species and its low breeding density
(hard-bodied with an external exoskeleton; in apparently “optimal” habitats
Stark, 1982). Their life cycle includes three (1pair/about 70 ha of old-growth conifer
phases (Stark 1982). The first is the forest), (2) the low detectability of the
process of colonisation in early to mid- species outside the normal periods of
summer, when beetles invade trees before drumming activities, and (3) the limited
they start to reproduce. The second is a prospection capabilities under spring snow
reproduction phase, which includes conditions.
mating, oviposition, and brood
development up to the time of emergence. 3.2. Study areas
The third is a natal dispersal phase. As for
other ectothermic organisms, ambient The data on woodpecker breeding
temperature has a major influence upon the parameters and food supply presented in
duration and timing of the different phases this thesis were collected between 1996
of development of the insect prey (Annila and 1999 in North Karelia, easternmost
1969, Salonen 1973, Post 1984). Beetle Finland (63°N, 31°E). The study area
emergence or timing of natal dispersal consisted of a patchwork of eight Norway
depends on the time of reproduction spruce-dominated old-growth stands and
(Annila 1969). In addition, the length of one Scots pine-dominated Pinus sylvestris
the life cycle depends on the species of stand burnt over in 1992. Among the eight
beetle and factors such as moisture content old-growth habitat patches, five were
of tree tissues and density of conspecifics surrounded by ditched clear-cuts and three
(Post 1984). were surrounded by untouched peatlands.
Several traits, however, distinguish bark As a result, the patches were spatially
and longhorn beetles. Bark beetles are isolated from the others. The shortest
small (< 6 mm in length) but very distance between two patches was 500 m,
numerous, and densely aggregated in the and the longest 66 km. Each patch (65-90
phloem (Powell 2000). Conifer bark ha) was annually inhabited by a single pair
beetles do not enter the sapwood of the tree of Three-toed Woodpeckers, except in
and remain inside the bark, where they go 1996 when a second pair was found
through their development. Emerging breeding just outside the burnt area, while
beetles then leave their brood trees from using it as a foraging area.
August to November, prior to hibernation The information on dispersal patterns of
(e.g., Annila 1969). By contrast, the wood- Three-toed Woodpeckers originates from
boring beetles can be much larger (up to 50 bird ringing activities carried out between
mm) but less numerous and less clumped 1973 and 2000 in Finland and Sweden.
than bark beetles (Powell 2000). Longhorn
beetles, whether shallow (e.g., Tetropium 3.3. General methods
sp., Rhagium sp.) or deep (e.g.,
143.3.1. The woodpecker data identified as different birds when they
were observed in forest stands a year
3.3.1.1. Reproduction before the capture of the second calendar
year individuals, or after the occurrence of
Fast drumming is used as a long-range colour-ringed residents (II, III, VI).
territorial signal early in the morning. It is Based on 6 hours per nest (with 2
performed by both sexes during the spring, consecutive hours’ observation per day
mainly from March to May, but also in late during the two last weeks of the rearing
summer-early autumn (P. Fayt, unpubl.). period), parental effort was estimated from
Patch occupancy was annually checked by the feeding frequency per hour and per
listening for drumming activities under nestling. Attention was paid to counting
natural conditions (without playback the number of wood-boring beetle larvae
induction). Nests were then actively sought delivered (e.g., longhorn beetle). The diet
from early May onwards all over the of the offspring was identified and
woodpecker habitats. They were annually quantified by using spotting scopes (II).
located by nest-excavation noises in early In order to relate local woodpecker
morning, by accidental discovery, usually reproductive output to ambient temperature
after the discovery of fresh wood chips on conditions, mean brood size was measured
the forest floor, and by the noisy annually from the same five habitat
vocalisations of the offspring. patches and related to the mean air
Breeding time was estimated from the temperature recorded during the preceding
fledging date instead of from the laying winter (November-March) and spring
date, by backward calculation from the (April-May). Winter and spring
date of fledging, to control for between- temperatures in the study area were
pair variation in the length of the estimated by taking an average of the
incubation and rearing periods. Fledging monthly mean temperatures measured
date corresponded to the number of days from the nearby weather station of Lieksa
from the 1st of June to the fledging day. Lampela (63°19’N, 30°03’E) (III).
Nests were visited daily once a nestling To see whether interspecific pressure
was seen extending its head from the may contribute to explain a significant part
cavity to beg for food; fledging was of the variation in the reproductive
considered to have taken place when the performances of resident Three-toed
first nestling had left the nest (II, III). Woodpeckers, I measured the breeding
To determine the brood size of the density and mean brood size of Great
woodpeckers it was necessary to climb the spotted Woodpeckers Picoides major
nest tree with metal shoes and use a small reproducing in the same habitat patch as a
mirror and flashlight to investigate the pair of Three-toed Woodpeckers. The
cavity. If the nestling count was uncertain, methods of finding nests and counting
the tree cavities were revisited during the nestlings were the same as those used for
following days. To avoid repeated brood Three-toed Woodpeckers (III).
size measurements from the same females,
woodpeckers were individually colour- 3.3.1.2. Dispersal patterns
ringed whenever it was possible. A total of
10 breeding females and 12 breeding males Higher numbers of juvenile woodpeckers
were trapped and colour-ringed. The birds would be expected to disperse in autumns
were captured after they entered the nest following warmer springs in the case that
cavity to feed the offspring by placing a temperature-dependent profitability of
plastic tunnel prolonged by a hoop net in insect prey is a factor explaining fitness
front of the nest hole. In addition, males variation among individuals (IV).
and females that could not be trapped were Accordingly, spring temperature (April-
15May) in Finland was annually related to Finland and Sweden, on the basis of
the following autumn number of dispersing additional information available from the
juveniles and to the winter population ringing records of the Swedish Museum of
density of the woodpecker (1973-1999). Natural History. Together with capture
The spring temperature throughout the coordinates and biometry, the yearly
country was estimated by taking an number of birds dispersing in Sweden was
average of the monthly mean temperatures compared to the yearly number of
measured from six weather stations; two dispersers in Finland. Woodpecker counts
stations were situated in southern Finland in Sweden were related to the total number
(61°N, 22°-28°E), two in central Finland of fully-grown birds ringed each year, as in
(63°N, 23°-30°E) and two in northern Finland.
Finland (65°N, 26°-29°E). The yearly
spring air temperature was calculated by 3.3.2. The insect prey data
taking an average of the monthly mean
temperatures recorded from the six In this thesis, habitat suitability for a
weather stations. The annual number of Three-toed Woodpecker was defined as a
dispersing woodpeckers was estimated function of available food supply, in terms
from the ringing data records of the of abundance throughout the year and
Finnish Museum of Natural History. profitability in relation to reproductive
Importantly, juveniles were only activities.
considered as dispersing individuals when
they were captured in localities known not 3.3.2.1. Prey abundance
to be breeding grounds of the woodpecker.
Because the number of woodpeckers Window-flight traps, a reliable sampling
captured every autumn might be connected device for bark beetles (Martikainen et al.
with the ringing activity effort, counts 1996, 1999), were used as the sampling
were made comparable by relating them to method to estimate local food abundance
the total number of fully grown birds within patches. A sampling effort of 1 trap
ringed each year and expressed as the per 7 ha was assumed to allow a
number of woodpeckers per 10,000 birds representative sampling of the patchily
ringed. Winter density was estimated by distributed forest beetles. Traps were
dividing the yearly number of individuals located after choosing their direction and
observed during the early- (01. – 14.11), distance from the centre of sample plots
mid- (25.12 – 07.01) and late- (21.02 – from random number combinations. The
06.03) census periods of the national yearly sampling period was 1 May–20
winter bird count (1975-99) with the total July, covering the main flying season for
length of census routes and transformed the beetles. Overall, ten traps were
into a population index. distributed all over each woodpecker
To investigate whether juveniles habitat patch; they were emptied twice
dispersed earlier from regions with an during the summer. During the whole
earlier prey development, the capture study period, insect populations were
coordinates of dispersing juveniles were sampled in about 1,590 ha of naturally
related to isotherms connecting points dynamic forest habitats. Catches from
where a mean temperature of 5°C is window traps yielded altogether 19,251
measured at different times in spring (i.e., individual beetles, which included 14,262
the temperature threshold when the bark beetles (74.1%) from 31 species (III,
woodpecker prey start moving and VI, VII). Estimates of prey abundance
developing again after hibernation). included the number of individual beetles
Patterns of woodpecker dispersal in of all the families, the number of bark
space and time were compared between beetles, the number of individual bark
16beetles of the species that specifically live adults)). On the basis of the sequential
on spruce, the number of individual wood- order of the beetles’ development stages
boring beetles (including the families (egg-larva-pupa-adult), an index of
Elateridae, Anobidae, Oedemeridae, development for the spruce bark beetle
Cerambycidae, Curculionidae), the number community was built up by dividing the
of longhorn beetles, and the number of number of adult beetles of the different
bark and longhorn beetle species. Scolytids species by the number of larvae collected
were classified as species living on spruce during the reproduction, post-reproduction,
according to the species assemblage found and natal dispersal periods of the
from the bark of spruce trees selected by woodpecker. Accordingly, it was assumed
the woodpecker (I, II, VI). In paper VII, that the earlier and/or faster the prey
bark beetle species were categorised community reproduction and/or
according to whether they live development is, the more adults and fewer
preferentially on standing dead trees or on bark beetle larvae should be collected and
logs, roots and stumps, as indicators of the higher the index should be. This
spatial variation in the distribution of method also assumed that the development
suitable woody microhabitats. time of the bark beetle community should
reflect the timing of development and
3.3.2.2. Prey profitability thereby the size-dependent profitability of
alternative prey, such as longhorn beetle
To clarify the diet preferences of the larvae (II, III).
woodpecker, to link prey profitability to
reproductive decisions, and to relate prey 4. RESULTS AND DISCUSSION
availability to natal dispersal, bark samples
from spruce trees bearing recent Three- 4.1. Diet preferences
toed Woodpecker foraging tracks were
collected during the pre-reproduction, In paper I, I looked at the insect content of
reproduction, post-reproduction, and natal the bark of trees selected by foraging
dispersal periods of the bird (I, II, III). Three-toed Woodpeckers. Bark samples
The first period coincided with late winter were taken from March to May, although
and ended with the start of nest excavation; most samples were collected in the first
the subsequent reproduction period lasted two months. In agreement with earlier
until fledging. The natal-dispersal period results from the Northern Hemisphere,
was defined on the basis of information whether from stomach or dropping
provided by ringing records (the dispersal analyses, I found the predatory
time of young woodpeckers at the habitat woodpecker to have particularly narrow
level was thus inferred from information dietary requirements outside the breeding
gathered at the landscape level). The post- season. Some 89% of the samples
reproduction period was then considered to originated from spruce trees, and 96.9% of
be the time between fledging and natal the insect prey collected were bark beetles.
dispersal. In order to minimise the multiple Interestingly, 78.5% of the adult bark
effects of tree host conditions on the beetles belonged to species previously
spatial distribution of beetle communities found to respond negatively to forest edge
on trunks, the samples (10x15 cm) were proximity by withdrawing into the interior
collected exclusively from standing trees, parts of forest stands. This led me to
at breast height. suppose that Three-toed Woodpeckers may
A total of 355 bark samples were suffer from lower winter foraging
collected, yielding 10,343 individual bark efficiency in a fragmented mature spruce
beetles (3,768 larvae, 950 pupae, and 5,625 forest landscape, if the proportion of
adults (including juveniles and sub- interior forest decreases.
174.2. Breeding density In paper II, I found that woodpecker
starting breeding earlier in habitats with
In paper VI, the hypothesis that the fewer bark beetle larvae and with more
autumn-winter food supply of the adult beetles sampled throughout the
woodpecker (the spruce bark beetles) season. In accordance with the above
control the subsequent woodpecker assumption, it is suggested that
breeding density was examined by woodpeckers nested earlier in forest
comparing the pattern of annual changes in habitats where the beetles reproduced
prey abundance between forest habitats earlier and/or development was faster, and
(burnt vs. old-growth) differing in the beetles emerged earlier. Brood size, in
disturbance history (accidental fire vs. turn, was inversely related to the number
regular small-scale gap dynamics created of spruce bark beetle larvae and pupae. Or,
by wind and tree-scale biotic interactions) conversely, brood size was larger in forest
and the woodpeckers’ numerical responses patches with more adult beetles. Thus,
to habitat change (decreasing vs. stable). In because the woodpecker bred earlier in
a forest patch burnt in 1992, where the habitats with more adults and fewer beetle
burned trees remained in the area to allow larvae, a seasonal decline was observed in
for natural development of the vegetation, woodpecker brood size, as is found in
a decline in the woodpecker breeding other woodpecker species and single-
population paralleled a progressive brooded birds in general (e.g., Wiktander
reduction in spruce bark beetle availability. 1998).
Neither the total number of individual In paper III, besides the effect of
beetles, the number of individual bark- and breeding time, I found patch-level
wood-boring beetles, nor the number of variation in the woodpecker brood size to
bark and longhorn beetle species showed be explained by the timing of bark beetle
significant trends after fire. In development and the number of bark and
neighbouring old-growth patches, on the longhorn beetle species, which were inter-
other hand, where one pair of woodpeckers correlated. Numbers of both beetle species,
bred annually, the abundance of spruce in turn, were strongly positively correlated
bark beetles did not change significantly with the abundance of longhorn beetles.
between years, although it differed among The breeding density and success of
patches. My results suggest that the coexisting Great spotted Woodpeckers did
woodpecker breeding population is limited not influence the Three-toed Woodpecker
by the level of food available outside the productivity. Neither were they correlated
breeding season, as shown for other forest with various estimates of animal food
bird populations (Perrins 1966, Van Balen supply.
1980, Hannon et al. 1987, Nilsson 1987). Thus, Three-toed Woodpeckers were
found to lay clutches earlier and to rear
4.3. Breeding performance larger broods in patches where the spruce
bark beetles developed earlier, where the
In papers II and III, I studied the effect of bark and longhorn beetle communities
prey profitability (based on the timing of were more diverse, and where longhorn
their development) on reproductive beetles were more abundant. Assuming a
decisions in Three-toed Woodpeckers, higher size-dependent profitability of
without taking into account and with longhorn beetle larvae in patches with
taking into account the potential effects of early bark beetle development, it is
confounding factors such as breeding time, proposed that brood size in the Three-toed
food abundance and level of interspecific Woodpecker depends on both abundance
pressure for available food resources, and phenology of Cerambycid beetle
respectively. larvae in relation to the bird breeding
18covered a relatively short period of time (4
years), the results would provide additional
3,5
evidence for the key impact of prey
3,0 profitability at the time of egg laying on
dispersal rate
Autumn natal
2,5 the bird’s reproductive decisions. The
2,0
results led to the prediction that the
1,5
1,0
number of dispersing juvenile
0,5 woodpeckers should increase with the
0,0 mean temperature of the preceding spring
(IV). In Finland, however, autumn
Early winter density
300
captures of juvenile woodpeckers and the
(01. - 14.11)
200 subsequent winter population size did not
increase with the spring temperature
100 conditions. Instead, woodpecker numbers
seemed to reach a maximum following
0 springs with a monthly mean temperature
400 of 4-6°C, although a considerable inter-
Mid-winter density
annual variation was apparent (Fig. 3).
(25.12 - 07.01)
300
Although this is a speculative proposal,
200
I suggest that this pattern is a result of the
100 decisions of breeding individuals to adjust
their heritable breeding date to the
0
development time of their prey, with
300
special reference to longhorn beetle larvae,
Late winter density
(21.02 - 06.03)
in an attempt to match breeding time and
200
nestling food profitability under variable
food abundance level.
100
0
1 2 3 4 5 6 7 8 H ig h p r e y a b u n d a n c e
Spring monthly mean temperature (°C)
Figure 3. Rate of natal dispersal (1973-
Fitness
1999) and winter population size (1975-
1999) of the Three-toed Woodpecker in
Finland as a function of monthly mean L o w p re y a b u n d a n c e
temperature of the preceding spring
(April-May).
C h a n g e in p r e y p r o f ita b ility
E a r ly L a te
cycle. This conclusion is in line with (T s > 4 -6 °C ) (T s < 4 -6 °C )
earlier findings, that productivity in birds
is largely determined by the amount of
food available to nestlings (e.g., Siikamäki Figure 4. Predicted fitness variation in
1995). breeding Three-toed Woodpeckers with
Like other woodpecker species that feed changing prey profitability (development
on bark- and wood-living arthropods time) under contrasting prey abundance.
(Hogstad and Stenberg 1997, Pasinelli Ts is the spring monthly mean T°.
1999), the mean brood size of the Three-
toed Woodpecker increased with spring Only with a monthly temperature of 4-6°
ambient temperature. Although the study in spring (April-May) (i.e., the temperature
19threshold when bark-living saproxylic 4.5. Natal dispersal
beetles such as bark beetles restart moving
and developing after hibernation) would In paper II, I investigated whether the
the parents be able to match breeding time onset of natal dispersal in the Three-toed
with food supply and to maximise their Woodpecker is related to change in prey
lifetime reproductive success. Even in the availability. To do so, I compared the
case of optimal timing of prey abundance of bark beetles living in spruce
development, however, food supply would trees in relation to the woodpecker
also depend on prey abundance, breeding cycle, after taking bark samples.
accounting for between-year variation in The dispersal period was inferred from
reproductive output and dispersal rate (Fig. information gathered at landscape level,
4). from ringing data files.
Besides a synchronous development of
4.4. Parental care the different beetle species, I found young
woodpeckers to disperse in Finland and
In paper II, nestlings from earlier/larger Sweden at the time when the abundance of
broods were found to receive more wood- the bark beetles in my study area (Eastern
boring beetle larvae than those from Finland) was lower than during the
later/smaller broods. Since the feeding rate preceding spring, in the reproductive and
did not change with breeding time and post-reproductive periods. Since a similar
brood size, I suggest that, in line with number of adult beetles was present in the
previous results, a seasonal decline in bark during the post-reproductive and the
wood-boring larva delivery rate is rather dispersal periods of the bird, despite a peak
caused by habitat-related differences in the in the number of juveniles and sub-adults
supply of the beetle larvae at the time of among the different species of beetles
brood rearing than by differential during the former period, this apparent
adjustment in parental effort between early reduction in food level seemed to result
and late breeders. Similarly, Hogstad and from the dispersal of synchronously-
Stenberg (1997) found White-backed developed beetle species within the habitat.
Woodpeckers Picoides leucotos to breed This is consistent with earlier results from
earlier, lay larger clutches and produce studies dealing with the population
heavier fledglings in years and places with ecology of bark beetles under boreal
warmer winter and early spring conditions, showing that the newly-formed
temperatures (and thus with the earliest beetles leave their brood trees from late
prey development). They also found that August to November, prior to hibernation
pairs breeding in warmer places (with a (Chararas 1962, Annila 1969). In addition,
shorter winter period) brought more wood- a review of the existing literature on the
boring larvae for their young compared to ecology of longhorn beetle larvae revealed
pairs from colder places, despite similar simultaneous changes in their availability,
feeding rates between the pairs from both due to gallery excavation deeper inside the
areas. As a result, fledglings were found to wood from the phloem, before pupation.
be the heaviest in the warmest habitats in These findings would suggest that a
spring. The heaviest fledglings were also sudden change in the spatial distribution of
the most likely to be recruited insect prey, whose timing is mediated by
subsequently into the local population, a the timing of the prey development, may
finding in agreement with the previously temporarily lower their availability for
found association between body size and foraging woodpeckers and promote the
survival among juvenile birds (e.g., van dispersal of young individuals. The
der Jeugd and Larsson 1988, Brinkhof et dispersal time of juvenile birds, on the
al. 1997). other hand, is known to affect their own
20lifetime reproductive success and, or regions should be, on average, smaller
therefore, also that of their parents than those coming from warmer habitats,
(Verboven and Visser 1998, Visser and as shown with White-backed Woodpeckers
Verboven 1999). This prompts me to (Hogstad and Stenberg 1997).
propose that, by using the profitability of In Finland, earlier-dispersing juvenile
prey at the time of egg-laying for the fine- males and females were, on average,
tuning of their reproductive decisions, longer-winged than their later-dispersing
female Three-toed Woodpeckers behave in counterparts. Wing length, in turn, is
a way that allows them to optimise their positively correlated with bill length
inclusive fitness. (Hogstad 1983). Body weight, on the other
Nevertheless, although my data hand, did not follow any linear seasonal
emphasised coincidence between change in trends, although an existing inter-
the spatial distribution of insect prey and correlation between weight and wing
the assumed onset of woodpecker natal length of male and female nestlings (P.
dispersal, this study suffered from the Fayt, unpulb.) suggested that this
absence of statistical verification that these discrepancy is a result of the limited
two phenomena are causally related. This sample size. In Sweden however, contrary
was due to the lack of direct field to the prediction, the body size of the
observations that young woodpeckers dispersers did not decrease with capture
effectively dispersed at times of changes in date. Instead, some of the juvenile males
prey availability. My results are therefore and females were found to be the heaviest
non-conclusive. and have the longest wings in the middle
of September, while earlier- and later-
4.6. Body size and dispersal patterns dispersing individuals were smaller. One
explanation for this could be the arrival in
In altricial birds, there is evidence that mid-September of larger individuals
fledgling size is related to hatch date (e.g., originating from Finland, as is suggested
Alatalo and Lundberg 1986, Brinkhof et al. by the dispersal patterns of juveniles on
1997), and that late-hatched individuals in both sides of the Baltic Sea.
a population disperse and search for vacant Regarding the dispersal patterns of
habitats later than do birds from early juveniles in relation to capture date, most
broods (Pinowsky 1965). This explains the individuals dispersing during the first half
general finding that early dispersers are of the dispersal period (August-September)
larger than late-dispersing juveniles were captured at the northernmost ringing
(Nilsson and Smith 1985, Hogstad 1990, stations in Finland and Sweden (63-65ºN)
Lens and Dhondt 1994). In paper IV, I while, from early October onwards,
examined the prediction that earlier- juveniles were mostly captured in the
dispersing juvenile Three-toed southern parts of the countries (58-60ºN).
Woodpeckers from a population should be Such a pattern would contradict the earlier
larger than later-dispersing ones, stated prediction, that juveniles from
presumably as a result of higher delivery warmer regions should disperse before
rate of wood-boring larvae in earlier those originating from colder northern
broods. In addition, if change in food regions.
availability promotes dispersal among Alternatively, one would expect early
juveniles, and if such a change is related to birds from warmer regions preferentially to
the life cycle of the prey, woodpeckers follow a northern direction, in order to
would be expected to disperse first from benefit from the still available developing
warmer areas (i.e., regions with earlier bark and wood-boring beetles hatched a
dates for the 5ºC isotherm in spring). Thus, year before. Only then would the later
individuals dispersing from colder habitats dispersers from colder regions fly
21southwards, to profit from the newly response to prey density, with population
growing bark beetle larvae. This is because densities increasing up to 44.8-fold during
spruce bark beetle larvae younger than 31/2 infestations, relative to those supported at
to 4 months of age are ignored by foraging endemic beetle levels. Furthermore,
Three-toed Woodpeckers (Koplin and comparison of beetle mortality inside and
Baldwin 1970), presumably being too outside woodpecker exclosures
small to be profitable. A consequence of demonstrated the potential of woodpeckers
this would be the capture of the earlier- to reduce up to 98% of spruce bark beetles
dispersing individuals in northern populations, depending on prey density
Fennoscandia, despite their southern and whether a study took the indirect
origin, from warmer regions. effects of predator feeding (desiccation,
Interestingly, the finding that seasonal parasitism, predation) into consideration.
variation in capture location coincided The review highlights several
with simultaneous increases in the ecological factors that are associated with
woodpecker average body size suggest the the predatory impact of the woodpeckers
possible occurrence of several somewhat and its variability. The population response
partially differentiated populations in of woodpeckers to prey density and
Fennoscandia. As discussed elsewhere predatory impact was a function of (1) the
(Dhondt et al. 1990, Blondel et al. 1993, woodpecker natal dispersal rate and
Blondel et al. 1999, Thomas et al. 2001), success, (2) the size-mediated profitability
predictable climatic variability across of the bark beetle larvae at the time the
landscapes and presumed limited dispersal bird is dispersing through the infestation,
(and thus gene flow) are pointed out as (3) limitations imposed by territoriality at
potential factors in promoting the the highest prey densities, (4) seasonal
evolution of those populations, by local variation in the caloric content of insect
adaptations of breeding adults to their prey and the metabolic rate and consequent
environment. For comparison, in Finland, food requirements of woodpecker species,
genetic diversity of isolated small and (5) stand-level factors that are related
populations of the Siberian Jay, another to site-specific silvicultural practices.
old-growth coniferous taiga forest dweller, This allows me to propose a general
has recently been found to be lower than mechanistic framework that accounts for
that of populations in continuous variation in the predatory impact of
distribution areas (Uimaniemi et al. 2000). woodpeckers on spruce bark beetles.
This was apparently attributable to low Overall, it stresses the close relationship
intrinsic natal dispersal capabilities in between the multi-scale heterogeneity of
fragmented forest landscapes. forested habitat, driven by succession and
disturbance patterns in space and time,
4.7. Predatory impact predator-prey population processes
operating at landscape levels, and local
In paper V, a literature review of case consumer-resource dynamics.
studies from the northern hemisphere Interestingly, in habitat patches where
revealed that, among woodpeckers preying Three-toed Woodpeckers were
on conifer bark beetles, the Three-toed continuously present, the abundance level
Woodpecker was the most responsive to of spruce bark beetles did not change
prey population changes. In comparison to significantly between years (VI).
other guild members (namely the Downy Conversely, the number of bark beetles of
Picoides pubescens, the Black-backed, P. the species on which the woodpecker does
arcticus and the Hairy Woodpeckers P. not prey (i.e., mainly Hylastes and
villosus), the Three-toed Woodpecker was Trypodendron spp.) showed significant
found to show the greatest numerical annual fluctuations. This result, although
22preliminary, suggests a stabilising role of time, due to differences in vulnerability
the woodpeckers on the population (location, length of exposure) to predation
dynamics of their prey. In accordance with under high woodpecker density.
this supposition, lower beetle populations
with more stable dynamics are expected in Autumn-winter food supply
Breeding density
forest patches where the predatory
Prey abundance
woodpeckers are regular or year-round Burnt forest
visitors than in patches where the
woodpeckers are rarely seen. Nestling food supply
Brood size
4.8. Habitat suitability
In papers VI and VII, I studied bark and
wood-boring beetle population responses Time after fire
to patch- and landscape-level management
history, as a prerequisite for developing
meaningful management plans for the
Three-toed Woodpecker.
Prey abundance Old-growth forest
In paper VI, I compared the short-term
effects of accidental fire vs. regular small
gap-dynamics on the woodpecker’s Autumn-winter food supply
abundance and its food supply. After fire, Breeding density
unlike the case of spruce bark beetles (the
autumn-winter prey whose abundance Nestling food supply
Brood size
declined through the years in parallel to the
woodpecker breeding population), the Time
abundance of longhorn beetles (the
nestling food supply) increased Figure 5. Illustrated annual changes in
progressively in parallel to the bird’s autumn-winter (spruce bark beetles) and
reproductive output. By contrast, in old- summer (longhorn beetle larvae) food
growth habitats, the continuous production supply of Three-toed Woodpeckers in burnt
of heterogeneity in forest structure allowed vs. old-growth patches, with implications
stable woodpecker-prey relationships, both for woodpecker breeding density and
in summer and in wintertime (Fig. 5). reproductive output.
Hence, this study shows that a patch
suitable for a wintering Three-toed In paper VII, I found the management
Woodpecker is not necessarily suitable for history of a forest landscape to influence
a reproducing individual, and vice versa. the spatial distribution of bark beetles
This is because the bird’s dietary within its inclusive old-growth habitat
requirements change seasonally, with units. Spruce bark beetle abundance was
autumn-winter and summer prey found to be lower at the edges of old-
responding differently to changing growth remnants in drained managed
heterogeneity. Alternatively, basing forest landscapes compared to patches
suppositions on the preceding results embedded in a swampy untouched
connecting the population dynamics of environment. Also, while the number of
conifer bark beetles with that of their avian bark beetle species did not change with
predators (V), it may be suggested that the distance from the edge in swamp forests,
contrasting population trends of bark and the number did increase from the edge into
wood-boring beetles after fire result from the interior part of remnants surrounded by
different mortality patterns in space and ditched clear-cuts. Comparing the
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