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...

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The population of male Kirtland's warbler (Dendroica kirtlandil) in the breeding season has averaged 206 from 1971 to 1987. The Kirtland's warbler occupies dense jack pine (Pinus banksiana) barrens from 5 to 23 years old and from 1.4 to 5.0 m high, formerly of wildfire origin. In 1984, 73% of the males censused were found in habitat naturally regenerated from wildfire or prescribed burning. The rest were in plantations (11 ~ or in harvested, unburned jack pine stands stocked by natural regeneration (16 ~ Twenty-two percent (630 of 2,886) of the Kirtland's warbler males counted in the annual censuses from 1971 through 1984 were found in 26 stands that were unburned and naturally regenerated following harvest. From 1982 to 1987, suitable regenerating areas were barely sufficient to replace currently occupied maturing stands, so population growth was impeded. Ecosystems of suitable size and regeneration characteristics (wildfire and plantation) doubled in area by 1989. In response, the population of Kirtland's warblers increased from 167 to 398 males between 1987 and 1992, but they withdrew almost entirely from the unburned, unplanted barrens by 1989 when the area of more suitable regeneration types increased. Minimum (368 males) and maximum (542 males) population estimates for 1996 were calculated based on 1984 average density (1.9 males per 40 ha) and peak population in burns (2.8 males per 40 ha).

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