Dawn M. Burke

Landscape Context and Fragmentation Effects on Forest Birds in Southern Ontario

Abstract We examined the effects of patch size, local forest cover, and regional forest cover on the numbers and species composition of forest birds detected during fixed-radius point counts in 287 forest patches in four replicate study areas in southern Ontario. Each study area consisted of two subareas differing in regional forest cover. The number of forest-interior species (as classified from the literature) detected per count, after controlling for forest patch size, tended to be higher in subareas with greater regional forest cover, but this effect was much stronger in some study areas than others. In contrast, numbers of edge species and interior-edge generalists were higher in subareas with lower regional forest cover. Within study areas, the number of forest-interior species increased and edge species decreased with both woodlot size and core area (amount of forest >100 m from an edge), but total species diversity at a point was relatively unaffected. Analyses of individual species generally corroborated the patterns, except that some so-called interior-edge generalists were more likely to be detected in large woodlots, while others were more likely in small woodlots. There was a tendency for the loss of forest-interior species with decreasing woodlot size to be greatest in subareas with low regional forest cover. In the context of highly fragmented landscapes such as southern Ontario, where many forest-dependent species have become rare, forest conservation should focus on protecting or restoring larger forest tracts in areas with substantial remaining regional forest cover. Efectos del Contexto del Paisaje y la Fragmentación sobre Aves de Bosque en el Sur de Ontario Resumen.  Examinamos el efecto del tamaño de parches y de la cobertura de bosque a escalas local y regional sobre el número y composición de especies de aves de bosque. Las aves fueron detectadas mediante puntos de conteo de radio fijo en 287 parches de bosque, en cuatro áreas de estudio replicadas en el sur de Ontario. Cada área de estudio consistió en dos sub-áreas, las que se diferenciaron en la cantidad de cobertura regional de bosque. Luego de controlar por el área de los parches, el número de especies de interior de bosque (clasificadas según la literatura) detectadas por conteo tendió a ser mayor en sub-áreas con mayor cobertura regional de bosque. Sin embargo, este efecto fue mucho mayor en algunas áreas de estudio que en otras. En contraste, los números de especies de borde y especies generalistas de borde-interior fueron mayores en las sub-áreas con menor cobertura regional de bosque. Dentro de cada área de estudio, el número de especies de interior de bosque aumentó y el número de especies de borde disminuyó con el aumento del tamaño y del área nucleo (cantidad de bosque a >100 m del borde) de los fragmentos de bosque, pero la diversidad total de especies en un punto no se vió relativamente afectada. Los análisis individuales por especie corroboraron los patrones observados, exceptuando que alguna especies llamadas generalistas de borde-interior tuvieron una mayor probabilidad de ser detectadas en fragmentos grandes, mientras que otras tuvieron mayor probabilidad en fragmentos pequeños. La tendencia más marcada a perder especies de interior de bosque con la reducción del área de los fragmentos ocurrió en las sub-áreas con baja cobertura regional de bosque. En paisajes en un contexto altamente fragmentado tales como en el sur de Ontario, donde muchas especies dependientes de bosque se han tornado escasas, la conservación de bosques debiera estar enfocada a la protección o restauración de grandes extenciones de bosque en áreas donde la cobertura regional de bosque es aún substancial.

IMPACTS OF HOUSING DEVELOPMENTS ON WOOD THRUSH NESTING SUCCESS IN HARDWOOD FOREST FRAGMENTS

Abstract We studied the impacts of low density, exurban housing developments on Wood Thrushes (Hylocichla mustelina) breeding in small forest fragments in two regions of rural southern Ontario. In both regions, Wood Thrushes breeding in woodlots with embedded houses (housing penetrating the forest border) experienced significantly higher rates of parasitism by Brown-headed Cowbirds (Molothrus ater) than Wood Thrushes breeding in woodlots with adjacent houses (houses within 100 m of the forest edge), or undeveloped woodlots (no houses within 100 m of the forest edge). Wood Thrushes breeding in Peterborough area woodlots with embedded or adjacent houses experienced significantly increased rates of nest predation compared to Wood Thrushes breeding in undeveloped woodlots. This increased nest predation resulted in significant reductions in seasonal productivity in developed woodlots. No increase in nest predation was experienced by Wood Thrushes nesting in developed woodlots in the Ottawa region. The effects of housing developments appear to be region-specific and may depend on other factors influencing the overall abundance of cowbirds. Impactos de la Construcción de Viviendas en el Éxito de Nidificación de Hylocichla mustelina en Fragmentos de Bosque Resumen. Estudiamos los impactos de la construcción en baja densidad de viviendas peri-urbanas sobre individuos de Hylocichla mustelina que se encontraron criando en fragmentos pequeños de bosque en dos regiones rurales del sur de Ontario. En ambas regiones, los individuos de H. mustelina que se reprodujeron en bosques donde había casas inmersas (que penetraban el borde del bosque) experimentaron tasas de parasitismo por Molothrus ater significativamente mayores que los individuos criando en bosques con casas adyacentes (dispuestas a menos de 100 m del borde del bosque), o en bosques no alterados por la presencia de casas (a más de 100 m del borde del bosque). Los individuos de H. mustelina que se encontraron criando en áreas boscosas de Peterborough, donde las casas estaban adentro o adyacentes al bosque, experimentaron incrementos significativos en las tasas de depredación de nidos comparados con individuos que criaron en bosques no alterados. Este incremento en la depredación de nidos llevó a reducciones significativas en la productividad estacional en los bosques con viviendas. No registramos un incremento en la depredación de nidos de H. mustelina en bosques con viviendas en la región de Ottawa. Los efectos de la construcción de viviendas parecen estar relacionados de modo específico con la región y podrían depender de otros factores que influencian la abundancia de M. ater.

Predation by Bears on Woodpecker Nests: Are Nestling Begging and Habitat Choice Risky Business?

ABSTRACT. We evaluated hypotheses explaining risk of predation by American Black Bear (Ursus americanus) at 418 Yellow-bellied Sapsucker (Sphyrapicus varius) and Hairy Woodpecker (Picoides villosus) nests, on the basis of nestling begging and nest-site habitat features in Algonquin Provincial Park, Ontario. Ninety-three percent of Yellow-bellied Sapsuckers in stands dominated by Sugar Maple (Acer saccharum) nested in Sugar Maple or American Beech (Fagus grandifolia) trees that were dead or in declining health, whereas 86% of Yellow-bellied Sapsuckers in stands dominated by aspen (Populus spp.) nested in Quaking Aspen (P. tremuloides) that were in declining health. Black Bears depredated 17% of 315 nests of Yellow-bellied Sapsuckers in Sugar Maple stands, which accounts for 71% of all Yellow-bellied Sapsucker nest failures. Only 1 (2%) of 46 Hairy Woodpecker nests in the same Sugar Maple stands was depredated by a bear. None of 51 Yellow-bellied Sapsucker nests in aspen stands was depredated. In Sugar Maple stands, daily nest survival of Yellow-bellied Sapsucker nests was lowest when nestling begging calls were loudest and carried the farthest, in more recently harvested stands, and in trees other than American Beech (mostly Sugar Maple). Nest substrates were hardest at Hairy Woodpecker nests, followed by successful Yellow-bellied Sapsucker nests in American Beech and Quaking Aspen; Yellow-bellied Sapsucker nests were softest in stands that had been harvested within the past 30 years. Our study suggests that the risk of predation by American Black Bears at woodpecker nests is a combined function of nestling begging calls, which attract bears to the nest, and nest habitat characteristics, which influence accessibility to the interior of the cavity.

Effects of Forest Management on Postfledging Survival of Rose-Breasted Grosbeaks (Pheucticus ludovicianus)

ABSTRACT. Many studies have examined the effects of forest fragmentation and management on songbird nesting success, but few have quantified postfledging survival, which is a critical component of population productivity. In 2005–2006, we estimated daily postfledging survival of Rose-breasted Grosbeaks (Pheucticus ludovicianus) by radiotracking 42 fledglings in forest fragments that had been managed by single-tree selection, by diameter-limit harvest, or as reference (not harvested for at least 25 years). Survival probability over the 3-week fledgling period was 0.62, and 86% of total fledgling mortality occurred during the first week out of the nest. Despite large differences in forest structure between forest management treatments, there was no effect of forest treatment on fledgling survival. Date of fledging, shrub cover, and patch size also had limited influence on fledgling survival. For all sites combined, females produced an estimated 0.23–0.37 recruiting daughters per year for the worst- and best-case scenarios of female fecundity and annual juvenile survival, which is lower than the expected annual mortality rate of breeding females (0.40–0.55). Even reference sites did not produce enough offspring to offset annual female mortality, which suggests that forest fragments in this region are population sinks.

Responses of insect pollinators and understory plants to silviculture in northern hardwood forests

Communities of flower flies (Diptera: Syrphidae), bees (Hymenoptera: Apoidea), and flowering plants were compared between harvested and unharvested hardwood stands in Algonquin Provincial Park, Ontario, Canada. Group-selection silviculture (where groups of trees are removed from a forested matrix, rather than single trees), increased the abundance of pollinators and flowering stems, but only after leaf-out. Wild red raspberry (Rubus strigosus) and bees benefitted most from the creation of canopy gaps. The combination of increased light, warm, bare soils, and abundant nectar-rich raspberry flowers probably created ideal habitat for soil-nesting bees, factors which are relatively absent from unharvested stands. By contrast, before leaf-out, spring ephemerals and high light-levels were universal and pollinators were even across treatments. More pollinators were caught in canopy gaps than in forested areas, and the proportion of fertilized ovules of spring beauty (Claytonia caroliniana) was higher in gaps than in the forest, suggesting that pollinators prefer foraging in gaps, even in spring. Group-selection silviculture in hardwood forests proved beneficial to native pollinating insects, at least in the short-term.

Logging affects fledgling sex ratios and baseline corticosterone in a forest songbird.

Silviculture (logging) creates a disturbance to forested environments. The degree to which forests are modified depends on the logging prescription and forest stand characteristics. In this study we compared the effects of two methods of group-selection (“moderate” and “heavy”) silviculture (GSS) and undisturbed reference stands on stress and offspring sex ratios of a forest interior species, the Ovenbird (Seiurus aurocapilla), in Algonquin Provincial Park, Canada. Blood samples were taken from nestlings for corticosterone and molecular sexing. We found that logging creates a disturbance that is stressful for nestling Ovenbirds, as illustrated by elevated baseline corticosterone in cut sites. Ovenbirds nesting in undisturbed reference forest produce fewer male offspring per brood (proportion male = 30%) while logging with progressively greater forest disturbance, shifted the offspring sex ratio towards males (proportion male: moderate = 50%, heavy = 70%). If Ovenbirds in undisturbed forests usually produce female-biased broods, then the production of males as a result of logging may disrupt population viability. We recommend a broad examination of nestling sex ratios in response to anthropogenic disturbance to determine the generality of our findings.

Ovenbird (Seiurus aurocapilla) Demography and Nest-Site Selection in Response to Single-Tree Selection Silviculture in a Northern Hardwood Managed Forest Landscape

Abstract: Ovenbird (Seiurus aurocapilla) demography and nest-site selection were examined in mature tolerant hardwood stands and stands at 3 stages of recovery (1–5, 10–15, and 20–25 y) following single-tree selection in the continuously forested landscape of Algonquin Provincial Park, central Ontario. This is one of a few studies to provide evidence of these responses in a continuously forested landscape. No differences in nesting success or finite rates of increase were detected among treatments. Ovenbirds were more selective of nest sites with deep leaf-litter and basal areas with a greater proportion of larger trees in recently harvested stands than in other stages of recovery. By 20–25 y post-harvest, most nest-site and random-plot microhabitat parameters did not differ. During the study, Algonquin Provincial Park was designated as a sink, probably due to heavy mast production in 2006, after which some mast-consuming small mammal populations increased by 9-fold, dramatically increasing rates of nest predation. Single-tree selection did not appear to affect ovenbird per capita productivity among stages of forest recovery, and by 20–25 y post-harvest many structural features of the forest had returned to pre-harvest conditions. Thus, in Algonquin Provincial Park, single-tree selection appears to be appropriate for maintaining sufficient ovenbird nest-site features by the end of the first cutting cycle. However, future source-sink modeling of this landscape should consider the influence of resource-pulse dynamics as an important parameter and track changes over the long term, to determine how sustainable populations of ovenbirds are within this region.

Conspecific and Interspecific Nest Reuse by Wood Thrush (Hylocichla mustelina)

Abstract We report one instance of conspecific nest reuse by Hylocichla mustelina (Wood Thrush) within the same breeding season, two instances of conspecific nest reuse in subsequent breeding seasons, and two instances of Wood Thrushes reusing nests originally constructed by Pheucticus ludovicianus (Rose-breasted Grosbeaks) during a three-year study in Ontario. Rates of nest reuse were higher than previously reported for Wood Thrush, with conspecific nest reuse accounting for 8–12% of the observed nesting activity, and interspecific nest reuse accounting for 8–9%. Nest reuse occurred following periods of colder minimum temperatures or greater precipitation than in other years. We suggest that instances of nest reuse within and between breeding seasons may occur in response to time or energy constraints on females resulting from unusual weather conditions. Documenting instances of nest reuse behaviour contributes to our understanding of some of the constraints experienced during breeding and may shed light on factors affecting annual reproductive success.

ASSESSING EDGE AVOIDANCE AND AREA SENSITIVITY OF RED-EYED VIREOS IN SOUTHCENTRAL ONTARIO

Abstract We assessed edge avoidance, area sensitivity, and the relationship between local and regional forest cover for nesting Red-eyed Vireos (Vireo olivaceus) in 13 forest fragments (1–2,353 ha in size) in southcentral Ontario, Canada. Red-eyed Vireo territories and nests were not significantly farther from the edge than random points in any of the forest fragments, and there was no relationship between the probability of a male pairing and the distance of the territory from the edge of the forest fragment. The density of singing males and the probability of a male being paired increased significantly with increasing local forest cover within a 2-km radius of a study site, but not with forest fragment area or regional forest cover within a 10-km radius. Nest success was low and the probability of a nest being parasitized by the Brown-headed Cowbird (Molothrus ater) or successfully fledging ≥1 host young did not vary with distance of the nest from the forest edge or with any of our area or forest cover measures. Red-eyed Vireos did not display edge avoidance nor did they appear to be area sensitive within our study region, but there was a positive relationship with the amount of local (2-km radius) forest cover. Maintaining localized regions with high forest cover has been recommended on numerous occasions for the conservation of area sensitive species; our results suggest high forest cover also may benefit species that do not appear to be area sensitive.

AGE RATIOS AND RETURN RATES OF ADULT MALE OVENBIRDS IN CONTIGUOUS AND FRAGMENTED FORESTS

Abstract We determined proportions and return rates of yearling and older territorial male Ovenbirds (Seiurus aurocapillus) in 12 forest fragments and two contiguous forest sites in southern Ontario to test the hypothesis that a larger proportion of second-year birds occupied forest fragments. There was no significant difference in the proportion of yearling birds among small, large and contiguous forests (small, 54.0%; large, 54.3%; contiguous, 44.9%). Return rates did not vary among fragment size categories (small, 34.4%; large, 35.7%; contiguous, 42.8%). Males in small fragments did not differ significantly from those in large fragments or contiguous forest in mass, wing length, or a condition index. Males also did not vary in these characteristics between age groups. These results suggest that male Ovenbirds in our study area do not occupy sites in proportion to their quality as breeding locations.