Managing ecological traps: Logging and sapsucker nest predation by bears (original) (raw)
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Predation by Bears on Woodpecker Nests: Are Nestling Begging and Habitat Choice Risky Business?
The Auk, 2009
Nous avons évalué des hypothèses expliquant les risques de prédation par Ursus americanus à nids de Sphyrapicus varius et de Picoides villosus en fonction des cris des oisillons et des caractéristiques de l'habitat aux sites de nidification au parc provincial Algonquin, en Ontario. Des S. varius habitant des érablières, % ont creusé des cavités dans des Acer saccharum ou des Fagus grandifolia morts ou défaillants tandis que % de ceux habitant des peupleraies (Populus spp.) ont niché dans des P. tremuloides défaillants. Des ours noirs ont détruit % des nids de S. varius dans des érablières, ce qui explique % de tous leurs échecs. Seulement sur nids (%) de P. villosus dans les mêmes érablières a été détruit par U. americanus. De nids de S. varius dans des peupleraies, aucun n'a échoué à cause d'un prédateur. Dans les érablières, le taux de survie quotidien des nids de S. varius était le plus bas lorsque les cris des oisillons étaient plus forts et portaient plus loin, dans les peuplements récemment exploités, et dans les essences (principalement A. saccharum) autres que F. grandifolia. Les parois des cavités de nidification étaient les plus dures aux nids de P. villosus, suivi par celles des nids réussis de S. varius dans les F. grandifolia et les P. tremuloides. Les nids de S. varius étaient les moins résistants dans les peuplements exploités pendant les dernières années. Notre étude suggère que le risque de prédation par U. americanus aux nids de pics est fonction des cris des oisillons (qui attirent des ours) et des caractéristiques de l'habitat (qui influent sur la possibilité d'accéder à l'intérieur du nid).
PLOS ONE, 2018
Despite the prevalent use of nest-site selection studies to define habitat quality for birds, many studies relying on use-availability analysis have found poor correlations between selected vegetation and reproductive success. Using 3 years of data from northeastern British Columbia (2007-2009), we determined timing of breeding from hatching dates and contrasted the nest-site selection of earlier (n = 22) with later-nesting pairs (n = 36) of yellowbellied sapsuckers (Sphyrapicus varius), because early breeders were expected to be more reproductively successful. We then compared these choices with those identified from useavailability analysis, and determined whether reproductive performance (fledgling production) was related to selected vegetation. None of the vegetation characteristics selected for nest sites from available vegetation predicted reproductive performance. Earlier-nesting pairs fledged more young on average than later breeders (4.41, SE = 0.18 versus 3.92, SE = 0.16), and chose less decayed aspen trees for nesting, that were surrounded on average by 3 times the number of food trees (paper birch, Betula papyrifera). Potential preference for birch trees was masked in the use-availability analysis, because the selection rate was dominated by the choices of the larger number of later-nesting pairs. Similarly, the majority (69%) of nest cavity entrances faced south, but earlier breeding pairs excavated northwardoriented cavities more frequently than did later breeding pairs, which strongly predicted their higher fledgling production. To our knowledge, our study is the first to compare the choices of early versus later breeders to test the efficacy of use-availability studies in defining habitat quality. We found that use-availability analysis was inadequate for determining vegetation characteristics related to reproductive performance. In contrast, measuring the distinct preferences of earlier breeders resulted in an improved ability to measure habitat quality and explain the spatial distribution of yellow-bellied sapsuckers, a keystone species of the mixedwood boreal forest.
2011
Cavity-nesting birds often have higher nesting success than birds that construct open cup nests (Martin and Li 1992, Johnson and Kermott 1994). Primary predators usually associated with predation of cavity nests in the western United States and Canada include squirrels (Tamiasciuris spp.), chipmunks (Tamias spp.), long-tailed weasels (Mustela frenata), and forest mice (Peromyscus species) (Li and Martin 1991, Walters and Miller 2001, Fontaine and Martin 2006). Black bears (Ursus americanus) account for few predation events involving nest contents of cavity-nesting birds (DeWeese and Pillmore 1972, Franzreb and Higgins 1975, Walters and Miller 2001). In this paper, I present data on black bear predation at nests of cavity-nesting birds within ponderosa pine (Pinus ponderosa) forests managed for timber production along the eastern slope of the Cascade Range in central Washington.
Habitat selection by black bears in an intensively logged boreal forest
Canadian Journal of Zoology, 2008
Extensive logging of the boreal forest rejuvenates landscapes once dominated by old-growth stands. As black bear ( Ursus americanus Pallas, 1780) fitness and behavior are known to be primarily related to the abundance of shade-intolerant soft mast species in northern forests, we hypothesized that logging will influence habitat and space use patterns of black bears. We used VHF telemetry on 12 female black bears in the Réserve faunique des Laurentides (Quebec, Canada) to investigate seasonal patterns of habitat selection in an exploited heterogeneous boreal landscape at different spatial scales. Habitat characterization based on seven forest cover types allowed us to compare the productivity of key forage species in various post-logging age classes. Regenerating stands (6–20 years old) had the uppermost ground vegetation cover, providing both the highest density and a high biomass of berries. Black bears preferred regenerating stands (6–20 years old) and avoided mature coniferous for...
2014
Given the importance of wildlife habitat protection in meeting land use management objectives, criteria for ''habitat'' identification are surprisingly amorphous. For example, while much current habitat modeling has tended to avoid the term ''niche modeling'', niche assumptions are implicit -meaning the presence of predators and competitors is essential to whether or not a species uses, or will use, an area. In this paper, we examine environmental variables associated with woodland caribou (Rangifer tarandus caribou) presence in the boreal forests of northwestern Ontario, Canada. Based on winter aerial surveys conducted in 2010-2013, we used logistic regression to identify important habitat characteristics (and/or their surrogates) and structural equation modeling (SEM) to explore causal and indirect caribou habitat relationships, at broad and fine scales. The best-fit regression model (>10,000 ha) to explain caribou presence, at the broad scale, included the presence of moose (Alces alces), wolves (Canis lupus), logging roads and primary roads, and all top models included wolves. In contrast, at the fine scale (<1000 ha), older, conifer forest was included in all of the top models of caribou presence. Using SEM, at broad scales, we found significant effects of increases in logging road density resulting in a direct increase in wolf presence, and indirectly in a decrease in caribou presence. However, at fine scales, we found significant direct positive effects between moose browse and moose presence, with indirect negative effects on caribou presence. We provide evidence that, at broad scales, habitat identification that includes logging roads and wolves provides a better measure of suitability of an area for caribou occupation than does forest cover alone. We suggest modeling of present or future habitat for woodland caribou will only be marginally effective if additional covariates of predation risk are not inclusive to the quantification of habitat supply.
Forest Ecology and Management, 2012
Single-tree selection harvesting is frequently used in the tolerant hardwood forests of North America but relatively little is known about how this silvicultural system affects wildlife, including many avian species. I investigated Rose-breasted Grosbeak (Pheucticus leudovicianus) habitat use, survival, and nestling provisioning behaviour in twelve hardwood stands in Algonquin Provincial Park which had been harvested by single-tree selection 0-5, 16-20, 21-25, and > 50 years previously. Density, pairing success, and the number of fledglings per successful nest were all significantly lower in the > 50 years post-harvest stands than in at least one other post-harvest treatment.
Habitat use by black bears in relation to conspecifics and competitors
Mammalian Biology - Zeitschrift für Säugetierkunde, 2008
Sympatric black bears (Ursus americanus) and brown bears (Ursus arctos) are common in many boreal systems; however, few predator assemblages are known to coexist on a single seasonally abundant large prey item. In lowland southwestern interior Alaska, black bears and brown bears are considered the primary cause of moose (Alces alces) calf mortality during the first 6 weeks of life. The objective of this study was to document habitat use of global-positioning system (GPS)-collared black bears during peak and non-peak seasons of black bear-induced and brown bear-induced moose calf mortality within southwestern interior Alaska, in spring 2002. We compared habitats of GPS-collared black bears to those of presumably uncollared black bears and brown bears at their moose calf mortality sites. Results from this study suggest that GPS-collared black bears use similar habitat as conspecifics more than expected during the peak period of black bear predation on moose calves, whereas they use habitat in proportion to home range availability during the peak in brown bear predation on moose calves. Sex-specific Ivlev's electivity indices describe greater than expected use of mixed-deciduous forest and needleleaf forest by male GPS-collared black bears during the peak of moose calf predation, whereas females have a tendency to use these habitats less than expected. Juvenile GPS-collared black bears largely use the same habitat as other sympatric predators during the peak of moose calf predation, whereas during the non-peak period juveniles use opposite habitats as adult GPS-collared black bears. The outcome of this study offers possible explanations (e.g., sex, age) for spatial overlap or segregation in one member of a complex predator guild in relation to a seasonal pulse of preferred prey.
Habitat Suitability for Williamson's Sapsuckers in Mixed-Conifer Forests
The Journal of Wildlife Management, 1993
Williamson's sapsuckers (Sphyrapicus thyroidem) have narrow habitat requirements and are sensitive indicators of change in intensively managed forest habitats of western North America. Thus, we studied habitat suitability for Williamson's sapsuckers at 99 4-ha sites (33 nest sites, 66 non-use sites) in mixedconifer forests in Arizona during 1991. Nesting success of sapsuckers was high in this habitat (93.2% nest success, 0.0014 daily mortality, n = 724 nest days), and they preferred to nest in tall (P < 0.05) aspen snags ( P < 0.001) near the bottom (P = 0.012) of snow-melt drainages with 0-20% of the canopies dominated by aspen. Sapsucker nest sites had particularly large (P < 0.05) live aspen and aspen snags in the surrounding area. Nest sites also had high (P < 0.05) snag densities (a = 7.65 snags/ha) in the surrounding area, and these snag densities exceeded those commonly used in forest management plans. Effective snag management should concentrate snags in groups within low-lying areas and conserve large-sized snags. A Habitat Suitability Index (HSI) correctly predicted that Williamson's sapsuckers should generally prefer drainages over ridgetops, but the model could not distinguish between use and non-use sites within drainages. Future HSI models for Williamson's sapsucker should continue to stress snag density, but should consider aspen snag density separately from density of other snags, incorporate height and diameter of aspen snags, and use a more liberal definition of aspens contributing to overstory canopy cover.
A landscape perspective of bird nest predation in a managed boreal black spruce forest
Écoscience, 2000
Several landscape level studies have reported that bird nest predation increases as forest cover decreases. These studies have mainly been conducted in agricultural or urban regions. However, few studies have explored relationships between forest cover and nest predation in boreal forests managed for timber harvesting. In 1997 and 1998, we evaluated bird nest predation in a mosaic of clearcuts and forest remnants dominated by black spruce (Picea mariana [Mill.] B.S.P.) and located north of Lake Saint-Jean, Québec. We used a 7 km × 9 km grid of sampling points to determine nest predation at four landscape scales (local vegetation, and 250 m, 500 m, and 1000 m radii around sampling points). Artificial nests (ground and arboreal) containing a common quail (Coturnix coturnix L.) egg and a plasticine egg were used to calculate predation pressure and to identify nest predators. Nest predation was high over the entire study area. Dominant predators were the gray jay (Perisoreus canadensis L.) and the red squirrel (Tamiasciurus hudsonicus Erxleben). Depredation by squirrels was influenced by local variables in 1997 and by landscape variables in 1998. In the latter case, depredation by squirrels increased as spruce cover increased. Depredation by gray jays was positively related to water body area and jack pine (Pinus banksiana Lamb.) cover. Squirrels preyed more on ground nests than on arboreal nests, while gray jays preyed almost exclusively on arboreal nests. We conclude that these predators probably impose different threats to different songbird species in boreal black spruce forests. Our results show that, in the short term, timber harvesting did not seem to increase predation in a boreal black spruce forest.