Habitat fragmentation has been shown to influence the abundance, movements, and persistence of many species. We asked the following questions: (1) Do species respond mainly to habitat loss or to the changes in habitat configuration resulting from this loss? (2) Do species exhibit sharp thresholds in their response to forest cover or configuration? We compared the relative influence of forest cover and configuration on 15 bird species in 33 landscapes (6.25 km2) in eastern Ontario, Canada. Forest cover in these landscapes varied between 3.4% and 66.8%. The metrics we used to quantify forest configuration were correlated to forest cover, so we regressed these configuration metrics against cover and used the residuals in logistic regression models. Of the 15 forest bird species included in the analyses, the presence of only 3 (Downy Woodpecker [  Picoides pubescens], Brown Creeper [Certhia americana], and White‐breasted Nuthatch [ Sitta carolinensis]) was not significantly related to either cover or configuration of woodland. Forest cover and configuration each were significant predictors of the presence of 6 species in landscapes occupied in both years, and 3 species responded both to cover and configuration. Models based on single years showed variability in the landscape characteristics that were significant predictors of the presence of each species. These results indicate that (1) landscape structure was an important predictor of bird distribution, (2) both forest cover and configuration were important predictors of species presence, and (3) responses were species‐specific. Effects of forest cover and configuration on species presence generally were not characterized by sharp thresholds, preventing the application of simple management rules. Although forest cover is an important feature of landscape structure, our results indicate that woodland configuration is a far from negligible component that should also be incorporated in conservation strategies.

Summary Research addressing the effects of habitat fragmentation on species, assemblages or ecosystems has been fraught with difficulties, from its conceptual foundation to statistical analyses and interpretation. Yet, it is critical to address such challenges as ecosystems are rapidly being altered across the world. Many studies have concluded that effects of habitat loss exceed those of fragmentation per se, that is, the degree to which a given amount of habitat is broken apart. There is also evidence from different biomes and taxa that habitat configuration, that is, the spatial arrangement of habitat at a given time, may influence several landscape processes such as functional connectivity, edge and matrix effects, and thus population viability. Instead of focusing attention on the relative influence of either habitat loss or fragmentation, we must identify portions of the gradient in habitat amount where configuration effects are most likely to be observed. Here, we suggest that all species are, to a certain degree, sensitive to landscape change and that, assuming a homogeneous matrix, habitat configuration will have a higher influence on species at intermediate values of habitat amount, where configuration has potentially the greatest variability. On the basis of empirical studies and simulations, we expect that species that are relatively tolerant to fragmentation of their habitat will exhibit a wider band where amount and configuration interact compared to species less tolerant to fragmentation. Synthesis and applications. Reducing habitat loss should be a top priority for conservation planners. However, researchers should also investigate the indirect impacts of habitat loss on biodiversity through fragmentation effects. This research aims to identify windows of opportunity where habitat configuration can mitigate to some extent the effects of habitat loss, particularly through the maintenance of functional connectivity.

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We conducted a 3‐year field experiment to measure the frequency of bird movements through riparian buffer strips before and after harvesting of adjacent forest. Our study was conducted in the boreal mixed wood forest of Alberta and was designed to determine empirically whether songbirds use riparian buffer strips of forest connecting forest reserves as corridors and if they move along these buffer strips more frequently than they cross adjacent clearcuts. We used mist nets to obtain an index of the frequency of bird movement in the forest, and we observed bird movements across adjacent clearcuts for comparison. We predicted that the frequency of movement would be greater (1) in buffer strips after harvesting of adjacent forest than before harvesting, (2) in buffer strips than across clearcuts and, (3) in buffer strips than at control sites (lakeshore forest with no adjacent clearcuts). After adjusting for year‐to‐year variation in abundance, we found that capture rates increased significantly from pre‐ to post‐harvest, but only for juveniles. Capture rates of adults decreased immediately after harvesting, probably because of the removal of an adjacent source of birds that previously moved through the lakeside forest. Movement rates of forest species in clearcuts were significantly lower than capture rates in the forest. The number of adults captured was positively correlated with the number of territories in the buffer strips, indicating that most birds captured were probably residents. The number of local territories was a poor predictor of juvenile captures, supporting the notion that juveniles were likely dispersing individuals. Our results indicate that buffer strips enhanced movements of juveniles (i.e., acted as corridors) and maintained movement rates of adults. Furthermore, there appeared to be a threshold distance between reserves below which birds may be less reluctant to fly across openings, making corridor use less important.

We review critical issues that must be considered when selecting indicator species for a monitoring program that aims to maintain or restore ecological integrity. First, we examine the pros and cons of different management approaches on which a conservation program can be based and conclude that ecosystem management is most appropriate. We then identify potential indicators of ecological integrity at various levels of the ecosystem, with a particular emphasis on the species level. We conclude that, although the use of indicator species remains contentious, it can be useful if (1) many species representing various taxa and life histories are included in the monitoring program, (2) their selection is primarily based on a sound quantitative database from the focal region, and (3) caution is applied when interpreting their population trends to distinguish actual signals from variations that may be unrelated to the deterioration of ecological integrity. Finally, we present and discuss different methods that have been used to select indicator species.

The notion that species might exhibit thresholds in their response to habitat alteration is appealing from a conservation perspective. Such thresholds could be used as targets for conservation in managed landscapes. In New Brunswick, Canada, forest management produces mosaics of varying stand age, species composition, and structure. We sampled this gradient in habitat suitability to examine the shape of species response functions and to look for evidence of statistically significant thresholds. We focused our attention on bird species breeding in late-seral forest and surveyed them at 390 point-count stations sampling broad-leaved deciduous to pure coniferous stands and a variety of silvicultural treatments (patch cutting, single-tree selection, spruce plantation [35-45 years old], and no recent treatment). A principal components analysis (PCA) on local vegetation separated stations along two axes reflecting gradients in stand composition and habitat alteration (increasingly open canopy and decreasing density of large trees/snags), respectively. We combined logistic regression and receiver-operating characteristic (ROC) analysis to detect thresholds in species occurrence along these gradients. Of the 42 species frequent enough to be included in the analyses, 13 (31%) showed a significant (p < 0.01) negative response to habitat alteration. Eight of the 13 species sensitive to habitat alteration exhibited thresholds in their occurrence after controlling for the suitability of local habitat. According to curves of the expected number of sensitive species ( based on their ROC-derived thresholds), canopy closure and the density of large trees (>30 cm dbh) should be at least 70% and 80 stems/ha, respectively, to expect to find the complete assemblage of bird species. However, these values should be viewed as liberal, given the nature of our response variable. More refined (e.g., fitness) parameters should be used to be conservative. Nonetheless, the approach allowed us to establish preliminary quantitative targets for conservation planning based on time-efficient sampling methods, and to explicitly account for the continuous variability existing within and among silvicultural treatments rather than to assume homogeneity within treatments.Umbrales en la Respuesta de Aves de Bosque a la Alteración del Hábitat como Objetivos Cuantitativos para la Conservación Resumen: La noción de que las especies pueden presentar umbrales en su respuesta a las alteraciones del hábitat es atrayente desde una perspectiva de conservación. Tales umbrales podrían ser utilizados como objetivos de conservación en paisajes bajo gestión. En Nuevo Brunswick, Canadá, la gestión de bosques produce mosaicos de bosques de edades, composición y estructura de especies diferentes. Muestreamos este la aptitud del hábitat en este gradiente para examinar la forma de las funciones de respuesta de las especies y para buscar evidencia de umbrales estadísticamente significativos. Centramos nuestra atención en la especies de aves que se reproducen en bosque sera...

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