Forest fragmentation, the disruption in the continuity of forest habitat, is hypothesized to be a major cause of population decline for some species of forest birds because fragmentation reduces nesting (reproductive) success. Nest predation and parasitism by cowbirds increased with forest fragmentation in nine midwestern (United States) landscapes that varied from 6 to 95 percent forest cover within a 10-kilometer radius of the study areas. Observed reproductive rates were low enough for some species in the most fragmented landscapes to suggest that their populations are sinks that depend for perpetuation on immigration from reproductive source populations in landscapes with more extensive forest cover. Conservation strategies should consider preservation and restoration of large, unfragmented "core" areas in each region.

Fragmentation of breeding habitat in North America has been implicated in the decline of forestnesting, Neotropical migrant birds. We used a comparative approach to examine the effects of fragmentation on three forest-nesting migrants: Ovenbird (Seiurus aurocapillus), Red-eyed Vireo (Vireo ofivaceus), and Wood Thrush (Hylocichla mustelina). We surveyed birds and monitored reproductive success on 28 study plots in fragmented and contiguous forests in two midwestern regions. Distribution of individuals between fragmented and contiguous forests appeared to vary among species and regions, but total nest failure was significantly higher in fragments than contiguous forests in both regions for all species (p = 0.053). We attributed greater nest failure to increased nest predation (p = O. 093) and increased brood parasitism by the Brownheaded Cowbird (Molothrus ater, p = 0. 009). In addition to greater total nest failure, partial nest faaure due Exito reproductivo de las aves migratorias en hhbitats fuente y sumidero Resutnen: La fragmentaci6n del hdbitat reproductivo en Norte Amdrica ha estado relacionada con la dismi-nuci6n de las ayes migratorias Neotropicales que anldan en los bosques. En este estudio usamos un mdtodo comparativo para examinar el efecto de la fragmentaci6n sobre tres ayes que anldan en los bosques: Seirus aurocapillus, Vireo olivaceus, y Hylocichla mustelina. Monitoreamos el dxito reproductivo en 28 parcelas en bosques fragmentados y continuos, en dos regiones geogrdtficas en el medio-oeste de los Estados Unldos. La distribuci6n de los individuos entre bosques fragmentados y continuos pareci6 variar entre especies y regiones, pero el fracaso total de los nidos fue stgntficativamente mdts alto en los fragmentos queen los bosques continuos, en ambas regiones para todas las especies (p = 0.053). Atribuimos los mayores fracasos de los nidos a la mayor depredaci6n (p = 0.093) y al mayor parasitismo por parte de Molothrus ater (P = 0.053). Ademdts del mayor fracaso total de los nldos, los fracasos parclales, debidos al parasitismo pot parte de Molo-1381 thrus ater, condujeron a una reducct6n en el ngmero de volantones de los hudspedes. St bidn las causas de la mortaltdad en los nidos parecteron ser especiflcas para carla especie, los fracasos torales y parctales de los nidos actuaron en forma conjunta reductendo el namero de descendientes por adulto en los fragmentos para las tres espectes. Usamos modelos stmples de crectmtento poblaclonal para evaluar la viabtlidad de las ires especies en hdbttats fragmentados y cont~nuos en ambas regiones. En general, las poblactones de los fragmentos parecteron ser poblaciones sumidero y las poblaclones en los bosques conttnuos parecieron ser poblaclones fuente. Asumiendo una mortaltdad constante durante el tnvterno, el crectmtento proyectado indtc6 queen ausencia de tnmigract6n, las poblactones de S. aurocapillus y V. olivaceus deberlan exttnguirse en los fragmentos en ambas regiones, y las poblaciones de H. mustelina deber~n mantenerse o declinar levemente en los fra...

Abstract. Migratory bird needs must be met during four phases of the year: breeding season, fall migration, wintering, and spring migration; thus, management may be needed during all four phases. The bulk of research and management has focused on the breeding season, although several issues remain unsettled, including the spatial extent of habitat influences on fitness and the importance of habitat on the breeding grounds used after breeding. Although detailed investigations have shed light on the ecology and population dynamics of a few avian species, knowledge is sketchy for most species. Replication of comprehensive studies is needed for multiple species across a range of areas.Information deficiencies are even greater during the wintering season, when birds require sites that provide security and food resources needed for survival and developing nutrient reserves for spring migration and, possibly, reproduction. Research is needed on many species simply to identify geographic distributions, wintering sites, habitat use, and basic ecology. Studies are complicated, however, by the mobility of birds and by sexual segregation during winter. Stable-isotope methodology has offered an opportunity to identify linkages between breeding and wintering sites, which facilitates understanding the complete annual cycle of birds.The twice-annual migrations are the poorest-understood events in a bird's life. Migration has always been a risky undertaking, with such anthropogenic features as tall buildings, towers, and wind generators adding to the risk. Species such as woodland specialists migrating through eastern North America have numerous options for pausing during migration to replenish nutrients, but some species depend on limited stopover locations. Research needs for migration include identifying pathways and timetables of migration, quality and distribution of habitats, threats posed by towers and other tall structures, and any bottlenecks for migration. Issues such as human population growth, acid deposition, climate change, and exotic diseases are global concerns with uncertain consequences to migratory birds and even lesscertain remedies. Despite enormous gaps in our understanding of these birds, research, much of it occurring in the past 30 years, has provided sufficient information to make intelligent conservation efforts but needs to expand to handle future challenges.

Abstract. Our understanding of migratory birds' year-round ecology and evolution remains patchy despite recent fundamental advances. Periodic reviews focus future research and inform conservation and management; here, we take advantage of our combined experiences working on Western Hemisphere avian migration systems to highlight recent lessons and critical gaps in knowledge. Among topics discussed are: (1) The pipeline from pure to applied researchers leaves room for improvement. (2) Population limitation and regulation includes both seasonal and between-season interactions. (3) The study of movements of small-bodied species remains a major research frontier. (4) We must increase our understanding of population connectivity. (5) With few exceptions, population regulation has barely been investigated. (6) We have increasingly integrated landscape configuration of habitats, large-scale habitat disturbances, and habitat quality impacts into models of seasonal and overall demographic success. (7) The post-breeding season (late summer for latitudinal migrants) is increasingly appreciated for its impacts on demography. (8) We recognize the diverse ways that avian brood parasites, nest predators, and food availability affect demography. (9) Source-sink and meta-population models help us understand migratory avian distributions among fragmented habitats. (10) Advances in modeling have improved estimates of annual survival and fecundity, but for few species. (11) Populations can be limited by ecological conditions in winter, but habitat needs are poorly known for most species at this time. (12) Migration tends to occupy broad spatial fronts that may change seasonally or when migrants cross major barriers. En route conditions can limit migrant populations; linking migration habitat quality indicators to fitness or population consequences presents a major challenge. (14) A variety of intra-tropical Neotropical migration patterns are recognizable, but almost nothing is known about these systems beyond descriptions of a few typical species' movements. (15) Global climate change scenarios predict range and phenology shifts of Neotropical migrant bird populations that must be considered in conservation plans. Future studies will depend on new technologies and the integration of modeling with sophisticated, large-spatial-scale measurement and parameter estimation; whether the pace of research and management involving migratory birds can match the growth of environmental threats remains to be seen.

Conservation efforts are most effective when we have complete demographic information for a species of concern. Nevertheless, fundamental gaps in our knowledge of demography still exist for many taxa. For passerine birds, the period of time directly after young birds leave the nest and before they disperse and/or migrate (i.e., the post‐fledging period) remains an understudied life stage. We reviewed the literature on survival of passerine birds during the post‐fledging period to synthesize current knowledge on survival rates and the factors affecting these rates, and conducted a sensitivity analysis to explore the relationship between population growth and post‐fledging survival across the range of rates reported in the literature. Fledgling age was a strong predictor of survival, with the highest mortality occurring during the first 3 weeks after birds fledged. Among species, survival ranged from 0.23 to 0.87 during the first 3 weeks post‐fledging and increased with adult body mass and nestling period duration. The relatively high proportion (12 of 19; 63%) of studies that detected at least 1 habitat effect on survival indicates that management focused on post‐fledging habitat can improve survival. Sensitivity analyses indicated that post‐fledging survival rates less than approximately 0.4 require unrealistic overwinter survival rates of juveniles to prevent population decline, unless adult survival rates and seasonal fecundity are high. Post‐fledging survival is a useful metric for monitoring passerine populations because it sets the ceiling on first‐year survival, responds to habitat management, and leads to more comprehensive demographic models for songbirds. © 2014 The Wildlife Society.