André Desrochers

INFLUENCE OF FOREST COVER ON THE MOVEMENTS OF FOREST BIRDS: A HOMING EXPERIMENT

Habitat loss and fragmentation affect forest birds through direct loss of breeding habitats, detrimental edge effects such as increased nest predation and brood parasitism, and possibly by limiting movements among remaining forest patches. Despite indirect evidence suggesting that landscape-scale bird movements are constrained by open areas, skepticism remains because birds routinely cross inhospitable terrain during migration. Here, we report evidence from 201 independent homing trials showing that landscape composition and configuration influence the movements (1–4 km) of two neotropical migrant (Black-throated Blue Warbler, Dendroica caerulescens and the Ovenbird, Seiurus aurocapillus) and one resident (Black-capped Chickadee, Poecile atricapillus) forest bird species in Quebec, Canada. Trials consisted of translocating territorial, mated males and measuring the time they needed to return to their territories (homing time), as well as the probability with which they returned to their territories within...

Gap-crossing decisions by forest birds: an empirical basis for parameterizing spatially-explicit, individual-based models

Spatially-explicit, individual-based models are increasingly used to evaluate the effects of habitat loss and fragmentation on habitat use and population persistence. Yet, they are criticized on the basis that they rely on little empirical data, especially regarding decision rules of moving individuals. Here we report the results of an experiment measuring the gap-crossing decisions of forest birds attracted to a recording of chickadee(Poecile atricapillus) mobbing calls, and provided with options to travel to the speaker by either crossing an open area (short cut) or taking a longer route under forest cover (detour). We performed the experiment in winter and late summer near Québec City, Québec, Canada. We recorded 1078 travel paths from 6 resident and 12 migratory species in 249 experimental sites. In both seasons, birds preferred to travel under forest cover rather than cross open areas, even when the forested detour conveyed a substantially longer route than the short cut in the open. Only when the detour under forest cover. This was considerably longer than the short-cut in the open, in both relative and absolute terms, were birds more likely to take short cuts, indicating that gap-crossing decisions are scale dependent. However, birds rarely ventured >25 m from forest edges despite having the opportunity to do so. Except for Hairy Woodpeckers (Picoides villosus) which ventured further into the open, all species showed similar gap-crossing decisions. Residents remained marginally closer to forest edges in late summer as compared to in winter. Conspecific group size had no influence on gap-crossing decisions. This experiment supports the hypothesis that forest bird movements are constrained in fragmented landscapes, and provides opportunities to calibrate spatially-explicit, individual-based models addressing the influence of landscape composition and configuration on dispersal.

Age and foraging success in European blackbirds: variation between and with individuals

Abstract Variation in foraging success among 284 colour-ringed European blackbirds, Turdus merula , was studied from 1988 to 1990, in Cambridge, U.K. One-year-old birds foraging on lawns were half as successful at getting large prey as 2-year-old birds, which in turn had slightly but significantly less success than older birds. There was no measurable change in foraging success among birds aged 3–5 or more years. Males and females of the same age had similar foraging success. Age-specific differences when foraging on leaf-litter were similar to those on lawns. Repeated measures from the same individuals over 2 years or more showed that the variation in foraging success among age groups at a given time was primarily due to an individuals own improvement. Given yearlings were cosistently ‘poor’ or ‘successful’ foragers at different periods of the year, but differences between individuals were smaller later in life. There was no relationship between the mean foraging performance of yearlings and their survival to the following year. There was significant seasonal change in bill length, but bill growth was probably insufficient to explain the variation in foraging success with age.

LANDSCAPE CHARACTERISTICS INFLUENCE POND OCCUPANCY BY FROGS AFTER ACCOUNTING FOR DETECTABILITY

2 Departement de phytologie, Pavillon Paul-Comtois, UniversiteLaval, Quebec, Quebec, G1K 7P4, Canada Abstract. Many investigators have hypothesized that landscape attributes such as the amount and proximity of habitat are important for amphibian spatial patterns. This has produced a number of studies focusing on the effects of landscape characteristics on am- phibian patterns of occurrence in patches or ponds, most of which conclude that the land- scape is important. We identified two concerns associated with these studies: one deals with their applicability to other landscape types, as most have been conducted in agricultural landscapes; the other highlights the need to account for the probability of detection. We tested the hypothesis that landscape characteristics influence spatial patterns of amphibian occurrence at ponds after accounting for the probability of detection in little-studied peatland landscapes undergoing peat mining. We also illustrated the costs of not accounting for the probability of detection by comparing our results to conventional logistic regression anal- yses. Results indicate that frog occurrence increased with the percent cover of ponds within 100, 250, and 1000 m, as well as the amount of forest cover within 1000 m. However, forest cover at 250 m had a negative influence on frog presence at ponds. Not accounting for the probability of detection resulted in underestimating the influence of most variables on frog occurrence, whereas a few were overestimated. Regardless, we show that conven- tional logistic regression can lead to different conclusions than analyses accounting for detectability. Our study is consistent with the hypothesis that landscape characteristics are important in determining the spatial patterns of frog occurrence at ponds. We strongly recommend estimating the probability of detection in field surveys, as this will increase the quality and conservation potential of models derived from such data.

Winter Responses of Forest Birds to Habitat Corridors and Gaps

Forest fragmentation and habitat loss may disrupt the movement or dispersal of forest-dwelling birds. Despite much interest in the severity of these effects and ways of mitigating them, little is known about actual movement patterns in different habitat types. We studied the movement of wintering resident birds, lured by playbacks of mobbing calls, to compare the willingness of forest birds to travel various distances in continuous forest, along narrow corridors (fencerows), and across gaps in forest cover. We also quantified the willingness of Black-capped Chickadees ( Poecile atricapillus ) to cross gaps when alternative forested detour routes were available. All species were less likely to respond to the calls as distance increased to 200 m, although White-breasted Nuthatches ( Sitta carolinensis ) and Hairy Woodpeckers ( Picoides villosus ) were generally less likely to respond than chickadees and Downy Woodpeckers (P. pubescens ). Chickadees were as likely to travel in corridors as in continuous forest, but were less likely to cross gaps as the gap distance increased. The other species were less willing to travel in corridors and gaps relative to forest, and the differences among habitats also increased with distance. For chickadees, gap-crossing decisions in the presence of forested detours varied over the range of distances that we tested, and were primarily influenced by detour efficiency (the length of the shortcut relative to the available detour). Over short distances, birds used forested detours, regardless of their efficiency. As absolute distances increased, birds tended to employ larger shortcuts in the open when detour efficiency was low or initial distance in the open was high, but they limited their distance from the nearest forest edge to 25 m. Thus, chickadees were unwilling to cross gaps of > 50 m when they had forested alternatives, yet they sometimes crossed gaps as large as 200 m when no such choice existed. Our results suggest that the presence of corridors enhanced the movement of some, but not all, forest birds, and that even chickadees, which were less sensitive to gap width, preferred not to venture far from forest cover.

The polygynandrous mating system of the alpine accentor, Prunella collaris. II. Multiple paternity and parental effort

Parentage was determined by DNA fingerprinting for 110 young from 38 broods. There was no intraspecific brood parasitism and no young were fathered by males from outside the polygynandrous group. Nineteen (50%) broods were fathered by one male (15 by alpha, four by beta), 17 by two males (14 alpha and beta, two alpha and gamma, one beta and gamma) and two by three males (alpha, beta and gamma). A males paternity share of a brood increased with his share of the matings, measured as the proportion of time he gained exclusive access to the female. This relationship was the same for alpha and beta males, which suggests that their copulations were of equal potency. Alpha males gained a larger share of the paternity by guarding fertile females and their overall paternity within the group tended to increase with female nesting asynchrony, although not significantly so, and to decrease with more competing subordinate males. Males were more likely to help feed nestlings if they gained a greater share of the matings with the mother. There was no difference between alpha and beta males in the relationship between the probability of helping and mating share. Given a choice between two synchronous broods, males preferred to help where their mating share was greatest. When alpha and beta males helped at the same nest their share of the feeds reflected their share of matings, not their dominance rank. When only one male helped at a nest, alpha males decreased their amount of help with decreased mating share, whereas beta males did not. This difference may arise because alpha males have greater chances of mating with other females in the group, so opportunity costs of helping are greater for them. How these different helping responses influence female preference for alpha versus beta males is discussed.

Sex, dominance, and microhabitat use in wintering black-capped chickadees: a field experiment

I studied foraging patterns of Black—capped Chickadees (Parus articapillus) wintering in flocks in poplar forests of central Alberta, Canada. Females exploited highest and outermost tree parts, while males (which socially dominate females) foraged low and close to trunks. Females spent more time probing and found fewer prey per probe than males, but both sexes had similar feeding rates. I temporarily removed all eight males from three flocks, females foraged lower and closer to trunks than in three control flocks. Experimental females spent less time probing than controls, but had similar feeding rates. When captive males were released, they returned to their flock and experimental females shifted back to their initial foraging behavior. The results show that sex—specific foraging patterns in this population were affected by avoidance by females of microhabitats used mostly by dominant males. I suggest that predator avoidance makes the tree parts exploited by males more profitable.

Effects of landscape structure on nesting songbird distribution in a harvested boreal forest

We studied the effects of forest cover and configuration on nesting songbird distribution in a harvested boreal forest. To emphasize landscape-level effects relative to stand effects, point count stations were established in mature stands only, but were surrounded by contrasting 100-ha landscapes. Seven of the 14 species studied responded significantly to landscape structure, but responses to specific landscape measures were found only in three species. Bay-breasted Warbler (Dendroica castanea) was absent from landscapes with <55% forest cover. Solitary Vireo (Vireo solitarius) also was associated with high forest cover per se. Conversely. American Robin (Turdus migratorius) was associated with poorly-forested landscapes. No species responded to mature forest configuration. Thus, clearcutting in boreal forests will reduce the use of remnant forest patches by certain species through a decrease of surrounding mature forest cover rather than changes in its spatial configuration.

Foraging ecology and use of drumming trees by three-toed woodpeckers

Among boreal forest bird species, the three-toed woodpecker (Picoides tridactylus) is closely associated with old-growth forests (>120 years), and possibly the most negatively affected by long-term changes induced by commercial forestry in eastern Canada. Part of this conflict is related to the woodpeckers use of standing dead trees as nesting sites. Moreover, this woodpeckers foraging behavior and its choice of feeding and drumming substrates may increase its vulnerability in managed forests. We describe foraging behavior of three-toed woodpeckers, and characterize foraging and drumming trees used by this species in Quebecs black spruce (Picea mariana) forests. During summer (May-Jul) and mid-winter (Jan-Feb), birds of both sexes used a highly specialized feeding technique consistent with searching for bark beetles (Coleoptera: Scolytidae). Snags were highly preferred over live trees as foraging substrates. Snags used for foraging had a greater diameter at breast height (dbh) and were less deteriorated than paired nearest available snags. When live trees were selected for foraging, they also had a greater dbh but were more deteriorated than nearest available live trees. Thus, only a limited number of trees had all characteristics preferred by foraging woodpeckers, probably as a result of the ecology of its phloem-boring prey. Snags also were highly preferred over live trees as drumming substrates. Drumming snags differed from paired nearest available snags by having a broken top, less bark cover, and a lower deterioration class, which probably provided better acoustic towers for territorial birds. Given the extensive use of snags with different characteristics for foraging and drumming by three-toed woodpeckers, models estimating snag requirements for this species based only on nesting requirements are probably of limited use to maintain populations in managed areas. Wildlife habitat management objectives that specifically require the maintenance and renewal of snags in early decaying stages found in old-growth forests are essential to the conservation of this woodpecker species in managed forests.

Age-Related Differences in Reproduction by European Blackbirds: Restraint or Constraint?

I present an experimental test of whether low foraging success in European blackbirds breeding for the first time causes their delayed breeding compared with older individuals