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Artificial nest experiments have been used in an attempt to understand patterns of predation affecting natural nests. A growing body of literature suggests that neither relative rates nor patterns of predation are the same for artificial and natural nests. We studied nest predation and daily mortality rates and patterns at real and artificial ground and shrub nests to test the validity of artificial nest experiments. We monitored 1667 artificial and 344 natural nests, over seven trials, in three regions, across 58 sites in Ontario. We controlled for many of the factors thought to be responsible for previously reported differences between predation rates on natural and artificial nests. Although artificial nests in our study resembled natural nests, contained eggs of appropriate size, shape, and color of target bird species, and were placed in similar microhabitats as natural nests, the rates of predation on these nests did not parallel rates on natural nests for any region in terms of absolute rate or pattern. Predation rates on artificial nests did not vary between years, as they tended to for natural nests, and the magnitude of predation pressure on artificial ground nests compared with shrub nests did not show the same pattern as that on natural nests. In general, rates of predation on artificial nests were significantly higher than on natural nests. Our results suggest that conclusions derived from artificial nest studies may be unfounded. Given that many influential ideas in predation theory are based on results of artificial nest experiments, it may be time to redo these experiments with natural nests.Resumen: Se han utilizado experimentos con nidos artificiales con la intención de entender los patrones de depredación que afectan a los nidos naturales. La bibliografía sugiere que ni las tasas relativas ni los patrones de depredación son iguales para nidos artificiales y naturales. Estudiamos las tasas y patrones de depredación de nidos y de mortalidad diaria en nidos reales y artificiales sobre el suelo y en matorrales para probar la validez de los experimentos con nidos artificiales. Monitoreamos 1667 nidos artificiales y 344 nidos naturales, en siete pruebas, en tres regiones, en 58 sitios en Notario. Controlamos muchos de los factores que se piensa son responsables de diferencias entre tasas de depredación en nidos naturales y artificiales reportadas previamente. Aunque los nidos artificiales en nuestro estudio se asemejaron a nidos naturales, contenían huevos de tamaño, forma y color adecuados para la especie de ave y fueron colocados en microhábitats 382 Predation Patterns on Artificial and Real NestsBurke et al.similares a los de nidos naturales, las tasas de depredación en estos nidos no fueron similares a las tasas en nidos naturales en ninguna región en términos de tasa o patrón absoluto. Las tasas de depredación en nidos artificiales no variaron de un año a otro, como fue la tendencia en nidos naturales, y la magnitud de la presión de depredación en nidos sobre el suelo comparada con nidos en arbu...

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To determine the minimum size requirements and influence of landscape context on reproductive success of forest‐breeding songbirds, we monitored nesting success of five species of songbirds on 40 fragments (12–2350 ha in total woodlot size) and two continuous forest sites in south‐central Ontario from 1994 through 1997. Woodlot size was the most important variable contributing to differences in reproductive success, with local forest cover (within a 10‐km radius) having no significant additional effect on productivity for any species. For all species, except Red‐eyed Vireo (Vireo olivaceous), adult female reproductive success was at or above replacement levels in large fragments (mean of 121 ha core area, 849 ha woodlot area) and continuous forest, and below replacement levels in small fragments (mean of 7.8 ha core area, 93 ha woodlot area). Red‐eyed Vireo productivity was particularly low, with single‐brooded females unable to maintain populations in any woodlots monitored, although populations were close to replacement levels in continuous forest. Only the very largest fragments acted as sources for Ovenbird (Seiurus aurocapillus) and Wood Thrush (Hylocichla mustelina) (i.e., >23 ha in core area, 225 ha in total woodlot area). Ovenbird and Wood Thrush were the most area‐sensitive, and Rose‐breasted Grosbeak (Pheucticus ludovicianus) and Veery (Catharus fuscens) the least, although all four species had significantly lower reproductive success in small as compared to large forest fragments. Reproductive success of Rose‐breasted Grosbeaks and Veery were similar in large forest fragments and continuous forest and were close to maintenance levels in small fragments, despite published reports of significant declines that might be attributable to poor productivity. Nest predation was the major cause of nest failure, with brood parasitism by Brown‐headed Cowbirds (Molothrus ater) further reducing the number of host young fledged from Ovenbird and Red‐eyed Vireo nests. Parasitism rates on the remaining species were very low and not analyzed statistically. Local forest cover had little effect on predation rate or rate of parasitism by Brown‐headed Cowbirds. Although local forest cover had little effect on reproductive success within fragmented landscapes, nest success was significantly higher in continuous forest than in all fragments combined for both Ovenbird and Red‐eyed Vireo. Our data show a poor agreement with Breeding Bird Survey population trend estimates for Ontario between 1986 and 1996. As only 1% of the forest fragments locally available are large enough to function as source habitats, we strongly advocate their preservation. We recommend preservation of forest tracts at least 500 ha in size, particularly woodlots with >90 ha in core area, to function as sources that will help guard against population declines on a local scale.

We examined the effects of patch size, local forest cover, and regional forest cover on the numbers and species composition of forest birds detected during fixed-radius point counts in 287 forest patches in four replicate study areas in southern Ontario. Each study area consisted of two subareas differing in regional forest cover. The number of forest-interior species (as classified from the literature) detected per count, after controlling for forest patch size, tended to be higher in subareas with greater regional forest cover, but this effect was much stronger in some study areas than others. In contrast, numbers of edge species and interior-edge generalists were higher in subareas with lower regional forest cover. Within study areas, the number of forest-interior species increased and edge species decreased with both woodlot size and core area (amount of forest >100 m from an edge), but total species diversity at a point was relatively unaffected. Analyses of individual species generally corroborated the patterns, except that some so-called interior-edge generalists were more likely to be detected in large woodlots, while others were more likely in small woodlots. There was a tendency for the loss of forest-interior species with decreasing woodlot size to be greatest in subareas with low regional forest cover. In the context of highly fragmented landscapes such as southern Ontario, where many forest-dependent species have become rare, forest conservation should focus on protecting or restoring larger forest tracts in areas with substantial remaining regional forest cover. Efectos del Contexto del Paisaje y la Fragmentación sobre Aves de Bosque en el Sur de Ontario Resumen.  Examinamos el efecto del tamaño de parches y de la cobertura de bosque a escalas local y regional sobre el número y composición de especies de aves de bosque. Las aves fueron detectadas mediante puntos de conteo de radio fijo en 287 parches de bosque, en cuatro áreas de estudio replicadas en el sur de Ontario. Cada área de estudio consistió en dos sub-áreas, las que se diferenciaron en la cantidad de cobertura regional de bosque. Luego de controlar por el área de los parches, el número de especies de interior de bosque (clasificadas según la literatura) detectadas por conteo tendió a ser mayor en sub-áreas con mayor cobertura regional de bosque. Sin embargo, este efecto fue mucho mayor en algunas áreas de estudio que en otras. En contraste, los números de especies de borde y especies generalistas de borde-interior fueron mayores en las sub-áreas con menor cobertura regional de bosque. Dentro de cada área de estudio, el número de especies de interior de bosque aumentó y el número de especies de borde disminuyó con el aumento del tamaño y del área nucleo (cantidad de bosque a >100 m del borde) de los fragmentos de bosque, pero la diversidad total de especies en un punto no se vió relativamente afectada. Los análisis individuales por especie corroboraron los patrones observados, exceptuando que alguna especies llamadas generalistas de borde-interior tuvieron una mayor probabilidad de ser detectadas en fragmentos grandes, mientras que otras tuvieron mayor probabilidad en fragmentos pequeños. La tendencia más marcada a perder especies de interior de bosque con la reducción del área de los fragmentos ocurrió en las sub-áreas con baja cobertura regional de bosque. En paisajes en un contexto altamente fragmentado tales como en el sur de Ontario, donde muchas especies dependientes de bosque se han tornado escasas, la conservación de bosques debiera estar enfocada a la protección o restauración de grandes extenciones de bosque en áreas donde la cobertura regional de bosque es aún substancial.

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