No abstract

Movements of organisms between habitat remnants can affect metapopulation structure, community assembly dynamics, gene flow and conservation strategy. In the tropical landscapes that support the majority of global biodiversity and where forest fragmentation is accelerating, there is particular urgency to understand how dispersal across habitats mediates the demography, distribution and differentiation of organisms. By employing unique dispersal challenge experiments coupled with exhaustive inventories of birds in a Panamanian lacustrine archipelago, we show that the ability to fly even short distances (< 100 m) between habitat fragments varies dramatically and consistently among species of forest birds, and that this variation correlates strongly with species' extinction histories and current distributions across the archipelago. This extreme variation in flight capability indicates that species' persistence in isolated forest remnants will be differentially mediated by their respective dispersal abilities, and that corridors connecting such fragments will be essential for the maintenance of avian diversity in fragmented tropical landscapes.

We present data from a study of early conifer regeneration and fuel loads after the 2002 Biscuit Fire, Oregon, USA, with and without postfire logging. Natural conifer regeneration was abundant after the high-severity fire. Postfire logging reduced median regeneration density by 71%, significantly increased downed woody fuels, and thus increased short-term fire risk. Additional reduction of fuels is necessary for effective mitigation of fire risk. Postfire logging can be counterproductive to the goals of forest regeneration and fuel reduction.

Historical and biogeographic contexts can play important, yet sometimes overlooked, roles in determining structure of local communities. In particular, few examinations of historical influences on patterns of species richness and relative abundances in tropical communities have been conducted. In part, that gap in our knowledge has been caused by a paucity of data on tropical communities, even for relatively well‐studied taxa such as birds. In the Neotropics, only two sites, a 97‐ha plot in lowland Peru and a 100‐ha plot in French Guiana, have been inventoried on a spatial scale sufficient to estimate population densities for a majority of resident bird species. Results from those studies revealed extremely similar species richness, community biomass, and patterns of relative abundance. A third site in lowland Panama was originally censused in 1968–1969 and has often been compared with many other tropical and temperate sites. Results from Panama suggested an exceptionally different community structure from that observed at the Amazonian sites. Informative comparisons among sites have been hampered, however, by differences in sampling protocols. The Panama site was sampled on a much smaller spatial scale (2 ha) than the two Amazonian sites. To improve comparisons, we censused a 104‐ha area (the Limbo plot) encompassing the original 2‐ha Panama study area and used several census methods, including those used at the Amazonian sites. As expected, spatial scale had a strong effect on estimates of species richness. We detected 252 species on the Limbo plot, compared with 161 detected on the original 2‐ha area. Estimates of total individual birds per 100 ha were similar, but estimates from the original study were based on densities measured for one‐third fewer species than we measured on our larger study area. Of the 53 species for which both Panama studies estimated population densities, a significant number of estimates were higher in the original study. Thus, the small spatial scale of the original study apparently led to inflated density estimates. The primary cause of disparities appeared to result from undersampling in the smaller plot of many species with patchy distributions and large territory sizes. Compared with Amazonian communities, the Panama community had far fewer rare species. Although 33% of species in Amazonian sites had densities of ≤1 pair/100 ha, only 17% were equally rare in Panama. Furthermore, eight species in Panama were, by tropical standards, “superabundant,” attaining densities as high as 212 breeding individuals/100 ha; the most abundant species in Amazonia barely reached one‐third of that number. In total, those eight species accounted for 36% of all individuals at Limbo. The median abundance at Limbo was 7 pairs/100 ha, vs. 2.5 pairs/100 ha in Amazonia. Consequently, the total number of birds on the Limbo study area was nearly twice that found in Amazonia, despite species richness being only three‐fourths as great. We conclude, first, that spatial scale has indeed had an important effect o...

Greater nest predation in tropical than temperate birds has been hypothesized to be a primary selective force generating latitudinal differences in avian life history traits. Few extensive data sets, however, have been available from tropical forests to compare with data from temperate forests. To increase the amount of empirical information available for addressing issues related to the evolution of life history traits of tropical birds, we measured the nesting success of understory birds in lowland forest of central Panama. We found and monitored the fates of 696 nests of 71 species over two breeding seasons. Daily nest predation rates for the ten species for which we obtained the largest samples ranged from 1.6 to 8.3%, equivalent to a loss of 43 to 92% of nests. These values overlapped extensively the range of daily predation rates experienced by ecologically similar species in North America. Proportion of nests fledging young, estimated with the Mayfield method, was significantly lower in tropical (range: 8 to 57%) than temperate (27 to 60%) species. Nesting success in Panama varied among years, however, being greater in 1996 than 1997. In 1996, nesting success was similar to that of species breeding in forest fragments of midwestern North America. When compared with success of nests in large, contiguous forest tracts of North America, however, tropical avian nesting success was consistently lower by approximately 23%. We conclude that nesting success in central Panama may be poor in most breeding seasons, but also may be punctuated by occasional years of relatively exceptional success, a possibility heretofore unappreciated because of a general paucity of data from the tropics. Furthermore, our results indicate substantial variation in levels of nesting success among species, and almost no variation in clutch size. Such large interspecific variation, as well as potentially large annual variation, in nesting success does not support the hypothesis that uniformly low levels of nesting success select for small tropical clutch sizes.

We evaluated the effects of perforation, or the creation of small gaps, within a mature, deciduous forest in southern Illinois (U.S.A.) on abundances of breeding birds. Openings of 0.02-0.4 ha were created by group and single-tree selection logging within a 2000-ha tract of forest. We used point counts to compare abundances of birds in uncut forest with those in similar adjacent forest compartments that were recently cut (1-5 years previously) and less recently cut (10-15 years earlier). Most species of forest birds were not significantly less common in logged tracts. Only Red-eyed Vireos ( Vireo olivaceus ) and Ovenbirds ( Seiurus aurocapillus ) were significantly more numerous in uncut forest, but the vireo responded negatively to cuts at sites on ridges only, not in ravines, whereas Ovenbird populations differed substantially among years. Blue Jays ( Cyanocitta cristata ), important nest predators, were significantly more abundant in cut than uncut forest, but brood parasitic Brown-headed Cowbirds ( Molothrus ater ) showed no consistent differences. Populations of gap-dependent species such as Hooded Warbler ( Wilsonia citrina ), Indigo Bunting ( Passerina cyanea ), Whiteeyed Vireo ( Vireo griseus ), and Carolina Wren ( Thryothorus ludovicianus ) were dramatically larger in recently cut forest, with populations of most species reaching a peak 2-3 years after cutting. Between 5 and 10 years after cutting, nearly all gap-dependent species had returned to population levels comparable to those in uncut forest. Species dependent upon larger gaps, such as Yellow-breasted Chat ( Icteria virens ), Blue-winged Warbler ( Vermivora pinus ), and Prairie Warbler ( Dendroica discolor ), were absent. We conclude that the first cutting cycle in selective logging had only a minor effect on the forest bird community composition and created a short-lived availability of habitat for gap species. In the southern Illinois landscape, selective logging appeared to add little to the existing effects of forest fragmentation. Effects of perforation may differ in more continuously forested landscapes, however, and may be influenced by total basal area of timber removed and by the length of the inter-cut interval. Efectos de la Tala Selectiva en Poblaciones de Aves de Bosque en un Paisaje Fragmentado Resumen: Evaluamos los efectos de la perforación, o creación de pequeños espacios dentro de bosques maduros deciduos sobre la abundancia de aves reproductoras en el sur de Illinois (E.U.). Se crearon espacios de 0.02-0.4 ha por medio de tala selectiva de grupo o de árboles individuales dentro de un espacio de bosque de 2000 ha. Utilizamos puntos de conteo para comparar abundancias en bosques sin cortar contra bosques adyacentes en condiciones muy similares y que fueron cortados recientemente (1-5 años) o menos recientemente (10-15 años). La mayoría de las especies de aves del bosque no fueron significativamente menos comunes en áreas taladas. Unicamente el vireo ojirrojo ( Vireo olivaceus ) y el chipe suelero coronado ( Seiurus aurocapillus )...

Recent technological innovation has opened new avenues in migration research – for instance, by allowing individual migratory animals to be followed over great distances and long periods of time, as well as by recording physiological information. Here, we focus on how technology – specifically applied to bird migration – has advanced our knowledge of migratory connectivity, and the behavior, demography, ecology, and physiology of migrants. Anticipating the invention of new and smaller tracking devices, in addition to the ways that technologies may be combined to measure and record the behavior of migratory animals, we also summarize major conceptual questions that can only be addressed once innovative, cutting‐edge instrumentation becomes available.

Since its isolation from the mainland more than 85 years ago, 65 bird species have disappeared from Barro Colorado Island, Panama. Because of these extinctions the island is often used as a model for the study of faunal relaxation, or loss of species through time. The most recent survey of the island 's bird community was completed in 1970. Between June 1994 and May 1996