In 1993 we conducted a follow‐up study of the 1987 survey by Griffith et al. (1989) of 421 avian and mammalian translocation programs in North America, Australia, and New Zealand to reassess the programs’ status and the biological and methodological factors associated with success. Our survey response rate was 81%. Approximately 38% of usable programs in 1993 reported a change in outcome from 1987 (e.g., a translocated population was “declining” but now is “self‐sustaining”), but the difference between the overall success rates was not statistically significant (66% in 1987 and 67% in 1993). Since 1987, an increase was observed in the median number of animals translocated per program (31.5 to 50.5), median duration of releases (2 to 3 years), and proportion of programs releasing more than 30 animals (46% to 68%). Multiple logistic regression analyses indicated that release into the core of the historical range, good‐to‐excellent habitat quality, native game species, greater numbers of released animals, and an omnivorous diet were positively associated with translocation success. Moreover, our results indicate that translocated birds were less successful at establishing self‐sustaining populations than translocated mammals. Our findings, using comparable logistic analyses, generally corroborate the results of Grifftth et al. (1989). Variables not found to be significantly correlated with translocation success include species’ reproductive potential (number of offspring and first age of reproduction), number and duration of the releases, and source of the translocated animals (wild‐caught versus captive‐reared).

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We studied avian biogeography and habitat selection in forests of southern Wisconsin ranging in area from 3 to > 500 ha. Bird diversity in these woodlots increases with area, due primarily to an increase in the number of forest—dwelling, long—distance migrants. We consider two possible explanations for this pattern: (1) area—dependent changes in forest vegetation, or (2) area—dependent change in interactions with competitors, predators, or brood parasites. We first describe vegetation structure and composition, then show that this description comprises important habitat features of forest birds. Bird habitat is characterized in three ways: (1) vegetational structure within bird territories is compared with that at random locations in the same woodlots, (2) structural characteristics of territories of different species are compared, and (3) factors related to species' abundance in different woodlots are analyzed. We found no area—dependent trends in vegetation structure or composition that seem likely to influence the bird community. However, forest—edge and farmland species increase in density as woodlot area decreases. We suggest that forest—edge and farmland species exclude certain forest—dwelling, long—distance migrants from small woodlots, and that this exclusion influences the bird community more than area—dependent changes in habitat or the degree of woodlot isolation.

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A stochastic computer model was used to examine the effects of varying degrees of habitat fragmentation on the dynamics of a hypothetical population of forest‐interior bid. The primary demographic parameter that influenced the population's dynamics was fecundity, which varied as a function of how far a birds territory was from an ecological edge. As our model landscape became more fragmented the proportion of forest habitat that was near edges increased geometrically, and the population's overall fecundity dropped as a result. The model demonstrates that impaired reproduction in a fragmented landscape is, by itself a sufficient disruption of the population's dynamics to generate population declines and shifts in distribution similar to those observed in the fragmented forests of southern Wisconsin. Without immigration of recruits from other regions where reproduction is better, habitat‐interior populations in a severely fragmented landscape can become locally extinct.

Predators are commonly thought to capture substandard individuals (those in poorer condition than the average individual) in higher than expected proportions, but evidence for this paradigm is scant, biased, and inconsistent. I describe the outcomes of 447 attacks by a trained Red—tailed Hawk (Buteo jamaicensis) on three species of typical mammalian prey (eastern chipmunks, cottontail rabbits, and gray squirrels). A strong correlation existed between the difficulty the hawk had capturing individuals of each species and the difference between the proportions of substandard individuals in the hawk's diet and the prey populations. The degree to which substandard individuals of a particular prey species are taken disproportionately by a predator seems to be a direct function of how difficult it normally is for the predator to capture and kill individuals of that species. A review of other studies shows a similar relationship between vertebrate predators and their prey.

The availability of winter food may strongly influence overwinter survival and, hence, limit certain bird populations in northern regions. Using the Jolly—Seber method of estimating survival rates from recapture and reobservation data, we compared the survival rates of 418 individually marked Black—capped Chickadees, Parus atricapillus, having access to supplemental food with those of 158 chickadees without access to supplemental food. During three winters (October through April, 1982—1985) chickadees with access to supplemental food had higher average monthly survival rates (95 vs. 87%), higher overwinter survival rates (69 vs. 37%), and higher standardized body masses (an additional 0.13 g) than birds on control sites. Differential survival occurred primarily during months with severe weather (> 5 d below —18°C). During these months, high energy demands probably made it difficult for birds without access to supplemental food to obtain sufficient energy from dispersed natural sources. In addition, during periods of extreme weather when foraging may be difficult, the extra fat carried by individuals that are supplementally fed may increase the probability of survival.

Impacts of habitat fragmentation on forest bird communities have often been studied in landscapes dominated by agriculture. The striking structural differences between forest fragments and the matrix have led most researchers to rely on island biogeographic theory to predict the distribution of bird species in fragmented forests. However, in some cases the vegetation surrounding fragments is not completely unsuitable for forest birds. Thus, a more general framework is needed to understand the effects of habitat fragmentation. The mosaic approach considers fragments as integrated parts of a complex landscape composed of patches of habitat of different qualities. In the coastal area of the Maule region in central Chile the remaining hualo (Nothofagus glauca) forests cover <10% of the landscape, are severely fragmented, and are imbedded in a matrix of exotic pine plantations. We compared the island and mosaic approaches as explanations for the distribution and abundance of forest birds. Variable circular plots were used to study the distribution of diurnal forest birds in hualo forest fragments and in the surrounding pine plantations. There was a negative relationship between the size of forest fragment and bird species richness per unit area. Fragmentation effects were mostly species‐specific. A few large‐sized bird species tended to be absent from the smaller fragments, while the presence or abundance of most birds showed no relationship with fragment size. The type of vegetation adjacent to forest fragments had a significant effect on the composition of the bird community inhabiting them. The abundance of most cavity‐nesting species in pine plantations was related positively to the proximity of either the nearest native forest fragment or the nearest creek. On the other hand, the frequency of most open‐nesting species in pine plantations was spatially unrelated to either forest fragments or creeks and depended mostly on the characteristics of the vegetation in the understory. Results support the use of the mosaic approach for the study of fragmentation on birds in forest‐dominated landscapes.