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We used repeated sightings of individual birds encountered in community-level surveys to investigate the relative roles of habitat and biological interactions in determining the distribution and abundance of each species. To analyze these data, we developed a multispecies N-mixture model that allowed estimation of both positive and negative correlations between abundances of different species while also estimating the effects of habitat and the effects of errors in detection of each species. Using a combination of single- and multispecies N-mixture modeling, we examined for each species whether our measures of habitat were sufficient to account for the variation in encounter histories of individual birds or whether other habitat variables or interactions with other species needed to be considered. In the community that we studied, habitat appeared to be more influential than biological interactions in determining the distribution and abundance of most avian species. Our results lend support to the hypothesis that abundances of forest specialists are negatively affected by forest fragmentation. Our results also suggest that many species were associated with particular types of vegetation as measured by structural attributes of the forests. The abundances of 6 of the 73 species observed in our study were strongly correlated. These species included large birds (American Crow (Corvus brachyrhynchos) and Red-winged Blackbird (Agelaius phoeniceus)) that forage on the ground in open habitats and small birds (Red-eyed Vireo (Vireo olivaceus), House Wren (Troglodytes aedon), Hooded Warbler (Setophaga citrina), and Prairie Warbler (Setophaga discolor)) that are associated with dense shrub cover. Species abundances were positively correlated within each size group and negatively correlated between groups. Except for the American Crow, which preys on eggs and nestlings of small song birds, none of the other 5 species is known to display direct interactions, so we suspect that the correlations may have been associated with species-specific responses to habitat components not adequately measured by our covariates.

For successful conservation of biodiversity, it is vital to know whether protected areas in increasingly fragmented landscapes effectively safeguard species. However, how large habitat fragments must be, and what level of protection is required to sustain species, remains poorly known. We compiled a global dataset on almost 2000 bird species in 741 forest fragments varying in size and protection status, and show that protection is associated with higher bird occurrence, especially for threatened species. Protection becomes increasingly effective with increasing size of forest fragments. For forest fragments >50 ha our results show that strict protection (International Union for Conservation of Nature [IUCN] categories I–IV) is strongly associated with higher bird occurrence, whereas fragments had to be at least 175 ha for moderate protection (IUCN categories V and VI) to have a positive effect. This meta-analysis quantifies the importance of fragment size, protection status, and their interaction for the conservation of bird species communities, and stresses that protection should not be limited to large pristine areas.

Powerline rights-of-way (ROWs) often provide habitat for early successional bird species that have suffered long-term population declines in eastern North America. To determine how the abundance of shrubland birds varies with habitat within ROW corridors and with land use patterns surrounding corridors, we ran Poisson regression models on data from 93 plots on ROWs and compared regression coefficients. We also determined nest success rates on a 1-km stretch of ROW. Seven species of shrubland birds were common in powerline corridors. However, the nest success rates for prairie warbler (Dendroica discolor) and field sparrow (Spizella pusilla) were <21%, which is too low to compensate for estimated annual mortality. Some shrubland bird species were more abundant on narrower ROWs or at sites with lower vegetation or particular types of vegetation, indicating that vegetation management could be refined to favor species of high conservation priority. Also, several species were more abundant in ROWs traversing unfragmented forest than those near residential areas or farmland, indicating that corridors in heavily forested regions may provide better habitat for these species. In the area where we monitored nests, brood parasitism by brown-headed cowbirds (Molothrus ater) occurred more frequently close to a residential area. Although ROWs support dense populations of shrubland birds, those in more heavily developed landscapes may constitute sink habitat. ROWs in extensive forests may contribute more to sustaining populations of early successional birds, and thus may be the best targets for habitat management.

We analyzed changes in abundance of terrestrial birds on St. John, U.S. Virgin Islands, for a 32 year period during which 3 major hurricanes occurred. Using 1987 as a baseline year, because it followed a 27 year hiatus when no major hurricanes hit the island, we assessed the impact of hurricanes on vegetation structure and bird populations. Bird abundance was determined for 25 m radius circular plots that were surveyed each year of the study along the same transects. Percent cover of trees, shrubs, and herbs was measured in each plot in 1987, 1990, and 2019. All of the survey plots were in moist forest or dry woodland in Virgin Islands National Park. Of 13 common birds, 5 did not show marked and consistent declines in abundance following hurricanes even though the structure of vegetation on the island was heavily modified by storms. Three of these species are insectivores. Seven species declined or showed habitat shifts following Hurricane Hugo in 1989, but 5 of these populations subsequently increased and most recovered to close to their 1987 abundance during the 1990s. Six of these 7 species also declined or showed habitat shifts following Hurricanes Irma and Maria in 2017. The most marked declines in the aftermath of hurricanes in both 1989 and 2017 were for frugivores and nectarivores, especially hummingbirds. Most common bird species in Virgin Islands National Park were either resistant to the effects of severe hurricanes or resilient in the decade following a hurricane. However, more research is needed to assess the status of vulnerable species such as hummingbirds and rare resident species (Bridled Quail-Dove [Geotrygon mystacea] and Puerto Rican Flycatcher [Myiarchus antillarum]).

We analyzed changes in abundance of terrestrial birds on St. John, U.S. Virgin Islands, for a 32 year period during which 3 major hurricanes occurred. Using 1987 as a baseline year, because it followed a 27 year hiatus when no major hurricanes hit the island, we assessed the impact of hurricanes on vegetation structure and bird populations. Bird abundance was determined for 25 m radius circular plots that were surveyed each year of the study along the same transects. Percent cover of trees, shrubs, and herbs was measured in each plot in 1987. 1990, and 2019. All of the survey plots were in moist forest or dry woodland in Virgin Islands National Park. Of 13 common birds. 5 did not show marked and consistent declines in abundance following hurricanes even though the structure of vegetation on the island was heavily modified by storms. Three of these species are insectivores. Seven species declined or showed habitat shifts following Hurricane Hugo in 1989. but 5 of these populations subsequently increased and most recovered to close to their 1987 abundance during the 1990s. Six of these 7 species also declined or showed habitat shifts following Hurricanes Irma and Maria in 2017. The most marked declines in the aftermath of hurricanes in both 1989 and 2017 were for frugivores and nectarivores, especially hummingbirds. Most common bird species in Virgin Islands National Park were either resistant to the effects of severe hurricanes or resilient in the decade following a hurricane. However, more research is needed to assess the status of vulnerable species such as hummingbirds and rare resident species (Bridled Quail-Dove [Geotrygon mystacea] and Puerto Rican Flycatcher [Myiarchus antillarum]). Received 9 April 2020. Accepted 22 February 2021.

We analyzed changes in abundance of terrestrial birds on St. John, U.S. Virgin Islands, for a 32 year period during which 3 major hurricanes occurred. Using 1987 as a baseline year, because it followed a 27 year hiatus when no major hurricanes hit the island, we assessed the impact of hurricanes on vegetation structure and bird populations. Bird abundance was determined for 25 m radius circular plots that were surveyed each year of the study along the same transects. Percent cover of trees, shrubs, and herbs was measured in each plot in 1987, 1990, and 2019. All of the survey plots were in moist forest or dry woodland in Virgin Islands National Park. Of 13 common birds, 5 did not show marked and consistent declines in abundance following hurricanes even though the structure of vegetation on the island was heavily modified by storms. Three of these species are insectivores. Seven species declined or showed habitat shifts following Hurricane Hugo in 1989, but 5 of these populations subsequently increased and most recovered to close to their 1987 abundance during the 1990s. Six of these 7 species also declined or showed habitat shifts following Hurricanes Irma and Maria in 2017. The most marked declines in the aftermath of hurricanes in both 1989 and 2017 were for frugivores and nectarivores, especially hummingbirds. Most common bird species in Virgin Islands National Park were either resistant to the effects of severe hurricanes or resilient in the decade following a hurricane. However, more research is needed to assess the status of vulnerable species such as hummingbirds and rare resident species (Bridled Quail-Dove [Geotrygon mystacea] and Puerto Rican Flycatcher [Myiarchus antillarum]). Analizamos los cambios en la abundancia de aves terrestres en St. John, en las Islas Vírgenes de los Estados Unidos, por un periodo de 32 años durante los cuales ocurrieron 3 grandes huracanes. Usando 1987 como el año base, porque éste siguió a una pausa de 27 años durante los cuales ningún gran huracán golpeó la isla, determinamos el impacto de huracanes en la estructura de la vegetación y las poblaciones de aves. La abundancia de aves fue determinada en parcelas circulares de 25 m de radio que fueron muestreadas cada año a lo largo de los mismos transectos. El porcentaje de cobertura de árboles, arbustos y hierbas fue medido en cada parcela en 1987, 1990 y 2019. Todas las parcelas de muestreo fueron hechos en bosques húmedos o arbolados secos del Virgin Islands National Park. De 13 aves comunes, 5 no mostraron declines marcados y consistentes en abundancia después del paso de huracanes si bien la estructura de la vegetación en la isla fue fuertemente modificada por estas tormentas. Tres de estas especies fueron insectívoros. Siete especies declinaron o mostraron cambios de hábitat después del huracán Hugo en 1989, aunque 5 de estas poblaciones subsecuentemente se incrementaron y la mayoría se recuperaron cercanamente a sus abundancias de 1987 durante la década de 1990. Seis de estas 7 especies también declinaron o mostraron cambios de hábitat después de los huracanes Irma y María en 2017. Los declines más marcados como secuela de huracanes en 1989 y 2017 fueron para frugívoros y nectarívoros, especialmente colibríes. Las especies más comunes en el Virgin Islands National Park fueron resistentes a los efectos de huracanes severos o resilientes en la década posterior a un huracán. Sin embargo, necesitamos más investigación para determinar el estatus de especies vulnerables como colibríes y especies residentes raras (la paloma Geotrygon mystacea y el mosquero Myiarchus antillarum).

Competition theory predicts that local communities should consist of species that are more dissimilar than expected by chance. We find a strikingly different pattern in a multicontinent data set (55 presence-absence matrices from 24 locations) on the composition of mixed-species bird flocks, which are important subunits of local bird communities the world over. By using null models and randomization tests followed by meta-analysis, we find the association strengths of species in flocks to be strongly related to similarity in body size and foraging behavior and higher for congeneric compared with noncongeneric species pairs. Given the local spatial scales of our individual analyses, differences in the habitat preferences of species are unlikely to have caused these association patterns; the patterns observed are most likely the outcome of species interactions. Extending group-living and social-information-use theory to a heterospecific context, we discuss potential behavioral mechanisms that lead to positive interactions among similar species in flocks, as well as ways in which competition costs are reduced. Our findings highlight the need to consider positive interactions along with competition when seeking to explain community assembly.

Cyclonic storms (often called hurricanes, typhoons, or cyclones) often cause population declines in vulnerable bird species, and the intensity of these storms appears to be increasing due to climate change. Prior studies have reported short-term impacts of hurricanes on avifauna, but few have examined long-term impacts. Over two decades (1993–2018), we periodically surveyed a subspecies of West Indian Woodpecker Melanerpes superciliaris nyeanus on San Salvador, a small island in The Bahamas, to determine its distribution on the island, habitat use, and effects of hurricanes on abundance and population size. We conducted passive and playback surveys, supplemented with mist-netting. Woodpeckers were found only in the northern part of San Salvador, despite extensive surveys throughout other accessible areas of the island. Birds occupied areas with taller coppice adjacent to sabal palm Sabal palmetto groves, which were used for nesting. After hurricanes with >160 kph winds passed over San Salvador, woodpecker densities declined to 35–40% of pre-hurricane densities, but generally recovered back to pre-hurricane densities within 2–3 years. Based on an estimated density of woodpeckers within a ~1,400 ha occupied area, we calculated a population size of approximately 240 individuals (CI = 68-408). However, the population declined to far lower numbers immediately following hurricanes. Under IUCN Red List criteria, M. s. nyeanus classifies as ‘Critically Endangered’, and could be especially sensitive to future hurricanes if they occur at a high enough frequency or intensity to prevent the population from rebounding. Given the small size, isolation, and vulnerability of this population, we recommend preservation of the core habitat, continued monitoring, and further research. Our study shows that small, threatened bird populations can be resilient to the effects of hurricanes, but increased intensity of hurricanes, in combination with other threats, may limit this resilience in the future.

When analyzing a table of statistical results, one must first decide whether adjustment of significance levels is appropriate. If the main goal is hypothesis generation or initial screening for potential conservation problems, then it may be appropriate to use the standard comparisonwise significance level to avoid Type II errors (not detecting real differences or trends). If the main goal is rigorous testing of a hypothesis, however, then an adjustment for multiple tests is needed. To control the familywise Type I error rate (the probability of rejecting at least one true null hypothesis), sequential modifications of the standard Bonferroni method, such as Holm's method, will provide more statistical power than the standard Bonferroni method. Additional power may be achieved through procedures that control the false discovery rate (FDR) (the expected proportion of false positives among tests found to be significant). Holm's sequential Bonferroni method and two FDR-controlling procedures were applied to the results of multiple-regression analyses of the relationship between habitat variables and the abundance of 25 species of forest birds in Japan, and the FDR-controlling procedures provided considerably greater statistical power.