Movements and Resource Selection of Fledgling Goshawks in Montane Forests of Southeastern British Columbia (original) (raw)
Related papers
Forest Ecology and Management, 2012
We studied reuse of Goshawk Accipiter gentilis nests after timber harvesting within 50 m from the nest in 31 territories in southeastern Norway. The proportion of nests used in the second or third breeding season after logging (55%) did not differ significantly from that of 27 control nests (67%). Both for all nests (N = 58), and for nests with logging closer than 50 m (N = 31), reused nests differed from those not reused by being situated in a larger area of mature forest, and in forests with a higher proportion of Norway Spruce Picea abies, which gives better cover than Scots Pine Pinus silvestris and deciduous trees. However, a higher proportion of nesting territories with the target nest situated in a Spruce-dominated forest stand seemed to lack alternative nests, probably due to the more intensive timber harvesting in Spruce-dominated landscapes. Hence, Goshawks' tolerance towards logging may be overestimated in Spruce-dominated forests. We recommend that foresters planning timber harvesting near Goshawk nests focus on the remaining mature forest stand and its structure. In order to maximise the chance of nest reuse, a patch of at least 2 ha of suitable mature forest around the nest should be retained.
Large-scale forest composition influences northern goshawk nesting in Wisconsin
The Journal of Wildlife Management, 2013
The northern goshawk (Accipiter gentilis atricapillus) is a woodland raptor that uses a variety of forest types for nesting across its breeding range, but strongly depends on older forests with large trees and open understories. Goshawks may select nesting locations by maximizing the convergence of nesting and foraging habitats. Insights into goshawk responses to heterogeneous landscapes can be gained by examining the location of active nest sites through time and at multiple spatial scales. We examined the landscape-scale forest conditions that influenced the probability of active goshawk nests in the United States Forest Service, Chequamegon-Nicolet National Forest (CNNF) in northern Wisconsin. We used goshawk nest survey and monitoring data from 1997 to 2006 to determine the probability of an active nest site over time in relation to forest composition and road density at 3 scales (200-m, 500-m, and 1,000-m radii). Goshawk nests were located primarily in upland hardwood (64%), conifer (23%), and older aspen-birch (!26 yrs old; 11%) habitat cover types. We used Bayesian temporal autoregressive models of nest locations across multiple spatial scales to analyze these data. The probability of active goshawk nest occurrence increased with increasing conifer cover (1,000 m) and decreased with increasing cover of older aspen-birch and density of primary roads (500 m). In addition, lesser proportions of older aspen-birch at intermediate scales around goshawk nests had a stronger effect on the probability of a nest being active than conifer and primary roads. Thus, the ratio of conifer cover (within 1,000 m) to older aspen-birch cover (within 500 m) in landscapes surrounding nest sites was the key driver in predicting the probability of an active nest site. This finding can be used by forest managers to help sustain the active status of a goshawk nesting area through time (i.e., annually), and foster goshawk nesting activity in areas where active nesting is not currently occurring. ß Published 2013. This article is a U.S. Government work and is in the public domain in the USA.
The Journal of Wildlife Management, 2012
Nest-site availability limits cavity-using populations in many harvested forests; however, little is known about the extent of nest-site limitation in mature forests with a full complement of excavator species and intact processes of cavity creation and loss. To examine the role of nest-site availability in limiting cavityusing populations in mature mixed conifer forests in central British Columbia, Canada, we conducted an 11-year before-after control-impact experiment in which we increased nest-site availability via nest box addition. Our 7 sites (3 treatments, 4 controls) had low cavity densities (<2/ha) prior to treatment and cavity occupation rates were also low (<10%/yr), which is a relationship often cited in the literature as evidence of non-limitation in cavity-nesting populations. Following nest box addition at our treatment sites, which tripled the availability of cavities, total density of bird and mammal nests more than tripled. Density of mountain chickadee (Poecile gambeli) nests increased 9-fold on treatment sites and returned to pre-treatment levels following box removal, suggesting that chickadee populations were limited by cavity availability at our study sites. Density of red squirrel (Tamiasciurus hudsonicus) and northern flying squirrel (Glaucomys sabrinus) nests and roosts also increased significantly at treatment sites following box addition and declined following box removal. We noted little change in chickadee or squirrel nest density at control sites monitored concurrently. Squirrels preferred large-sized over small-sized boxes, and significantly enlarged the entrance areas of small boxes by chewing, suggesting that there may have been a shortage of suitable nest and roost sites for them in our study area. We contend that low cavity occupancy rates may not accurately reflect nest-site availability for cavity nesters in mature forests, and that cavity size may influence the true availability of cavities on the landscape.
NESTING SUCCESS AND NEST PREDATORS IN FOREST FRAGMENTS: A STUDY USING REAL AND ARTIFICIAL NESTS
Auk, 2000
Area sensitivity in songbirds is commonly attributed to increased nest predation in forest fragments. In 1995 and 1996, we tested whether the nest predators and nesting success of an area-sensitive forest bird, the Eastern Yellow Robin (Eopsaltria australis), varied with fragment size, and we also conducted an artificial nest experiment. The study occurred in two small (55 ha) and two large (Ͼ400 ha) forest fragments in a matrix of agricultural land in New South Wales, Australia. Predation accounted for 95% of all failures of 282 robin nests, and the survival of robin nests was negatively correlated with how frequently we observed avian nest predators near nests (i.e. nest-predator activity). Of 461 artificial nests, 84% were depredated, nearly all (99%) by birds. Thus, birds were important predators of nests. The abundance, species richness, and activity of avian nest predators were not related to fragment size. Survival of robin nests averaged 19%; nests in small fragments had a 22% chance of producing at least one fledgling compared with 15% in large fragments, but the difference was not significant. Survival of artificial nests averaged 12% in both small and large fragments. Nest-predator activity accounted for the most variation (68%) in the fate of robin nests, followed by the cumulative density of open-cup nesters (16%). The placement of robin nests had no influence on nest fate. We conclude that nest predation was not area dependent and propose food supply as an alternative hypothesis to explain area sensitivity. We suggest that, rather than being related to fragment size, nest predation increases with decreasing forest cover in a landscape. Increased nest predation in fragmented compared with contiguous landscapes may lower the population viability of songbirds in a region, and hence regional numbers. Therefore, the spatial scale at which fragmentation influences nest predation and songbird populations must be considered carefully.
Nest-Site Habitat Use by White-Headed Woodpeckers in the Eastern Cascade Mountains, Washington
Northwestern Naturalist, 2003
The white-headed woodpecker (Picoides albolarvatus) is strongly associated with old-growth ponderosa pine (Pinus ponderosa) forest, a degraded and increasingly uncommon habitat in the Pacific Northwest. We investigated the nest-site habitat use of this species by collecting vegetation data at 21 known nest sites in the eastern Cascades of Washington, 12 of which we found in 1999. Sixteen of 17 (94%) nests in the ponderosa pine vegetation zone were in the 72% of the zone that occurred below 1219 m, and 15 (88%) nests were on slopes of Ͻ20% (which comprised 48% of the zone); the total area characterized by both slopes Ͻ20% and elevation below 1219 m was 181,664 ha or 33.6% of the vegetation zone. Most (16 of 21) nests were in ponderosa pines and 81% (17 of 21) were in snags. The nest snags and trees were generally large, with a mean diameter at breast height of 51.5 cm (s x ϭ 5.13). The mean height of nest snags and trees was 12.6 m (s x ϭ 2.33), and the mean height of the nest cavity entrance was 5.8 m (s x ϭ 1.37). Compared to random sites located Ͻ1 km from each nest, nest sites were characterized by a greater abundance, size, and basal area of large trees and snags, primarily ponderosa pines. Management of habitat for this species should include retention of 6 to 8 large snags/0.8 ha and 8 to 10 large trees/0.8 ha in the immediate vicinity of nesting areas. Habitat requirements at the home range scale should be investigated.
Avian Nest Success in Midwestern Forests Fragmented by Agriculture
The Condor, 2004
We studied how forest-bird nest success varied by landscape context from 1996 to 1998 in an agricultural region of southeastern Minnesota, southwestern Wisconsin, and northeastern Iowa. Nest success was 48% for all nests, 82% for cavity-nesting species, and 42% for cup-nesting species. Mayfield-adjusted nest success for five common species ranged from 23% for the American Redstart (Setophaga ruticilla) to 43% for the Eastern Wood-Pewee (Contopus virens). Nest success was lowest for open-cup nesters, species that reject Brown-headed Cowbird (Molothrus ater) eggs, species that nest near forest edges, and Neotropical migrants. The proportion of forest core area in a 5-km radius around the plot had a weakly negative relationship with daily survival rate of nests for all species pooled and for medium or high canopy nesters, species associated with interior and edge habitats, opencup nesters, and nests located between 75 and 199 m from an edge. The proportion of forest core area was positively related to daily survival rate only for ground and low nesters. Our findings are in contrast to a number of studies from the eastern United States reporting strong positive associations between forest area and nesting success. Supported models of habitat associations changed with the spatial scale of analysis and included variables not often considered in studies of forest birds, including the proportion of water, shrubs, and grasslands in the landscape. Forest area may not be a strong indicator of nest success in landscapes where all the available forests are fragmented. 6 Present address: USDA Forest Service, Alaska Region, Juneau, AK 99802.
We conducted a 3-year nest predation experiment with artificial ground nests in a boreal forest landscape to investigate the impact of landscape structure (clear-cuts, forest edges, interiors and corridors) on nest predation. The artificial nests in forest corridors had clearly lower predation (12.6%) than nests in clear-cuts (42.5%), forest edges (40.8%), and forest interiors (36.1%) in every year studied. The width of a corridor and the effects of forest-open land edge did not affect nest loss. During the three successive years, the nest predation rate was rather equal between forest and clear-cuts and in one year was highest in clear-cuts.
DOES SURVEY METHOD BIAS THE DESCRIPTION OF NORTHERN GOSHAWK NEST-SITE STRUCTURE
Abstmrr: Past str~dies on the nesting habitat of northern goshawks (Accipiter gentilis) often relied on nests fomid opportunistically, either during timber-sale operations, by searching apparently "good goshawk habitat, or 1)y other search methods where areas were preselected based on known forest conditions. Therefore, a bias in the characterimtion of habitat surrounding northern goshawk nest sites may exist toward late-forest structure (large trecs, high canopy closure). This potential problem has confo~~nded interpretation of data on nesting habitat of northern gosl~a\vks and added to uncertainty in the review process to consider the species for fcderal listing as threatened or endangcred. Systematic srtnley methods. which strive for complete coverage of an area and often llse broadcasts of conspecific calls, have been developed to overcome these potential biases, but no str~dy has compared habitat characteristics around nests foi~nd opport~~nistically with those found systematic~~llv. We compared habitat characteristics in a 0.4-ha area aror~nd nests found systematically (n = 27) versus those found opporti~nistically (11 = 22) on 3 national forests in eastern Oregon. \Ve found that both density of large trees (systematic: r = 16.4 + 3.1 trees/ha; r t SE; opportunistic: f = 21.3 2 3.2; P = 0.56) and canopy elosi~re (systematic: .t = 72 2 2%; opportunistic: .f = 70 + 2%; P = 0.61) \xlere similar around nests found wit11 either search method. Our results diminish concern that past survey methods mischaracterized northern goshawk nest-site s t~~i c t u r e .