Nesting Success of a Neotropical Migrant in a Multiple-Use, Forested Landscape

Abstract: We studied the nesting success of an individually marked population of Kentucky Warblers ( Oporornis formosus ), a species that nests in disturbed and undisturbed forests, in a heterogeneous, managed forest site in the Shawnee National Forest in southern Illinois from 1992 to 1995. We examined the effects of forest stand type (clearcuts of various ages, tree plantations, and older forest) and distance from habitat edges on rates of nest predation and brood parasitism by Brown-headed Cowbirds (   Molothrus ater ). Brood parasitism levels gradually decreased from 60% to 3% ( nests) over a distance of 2 km from an agricultural edge proximal to a known cowbird foraging site (a pig feedlot), but they did not vary with distance from any other kinds of edges or with forest stand type. Rates of nest predation ( nests) did not vary with distance from any edges, but they were significantly lower in older forest than within even-aged clearcuts, a tree plantation, and in successional vegetation adjacent to a residential facility. These results suggest that, even in fragmented landscapes with high overall levels of parasitism and nest predation, management practices within and immediately adjacent to forest tracts can affect the nesting success of some species, but not necessarily as a simple function of distance from edge. For the Kentucky Warbler, our results suggest that a management strategy that avoids even-age silviculture and leaves core stands of older forest far from cowbird feeding areas can increase nesting success to levels similar to those measured in more forested landscapes.     

Nesting Success of Neotropical Migrant Songbirds in a Highly Fragmented Landscape

Abstract: Small forests in agricultural landscapes are generally thought to be population sinks where the nesting success of Neotropical migrant songbirds is too low to sustain populations. In 1996 and 1997, we assessed the nesting success and productivity of Wood Thrushes (  Hylocichla mustelina ) and Rose-breasted Grosbeaks (  Pheucticus ludovicianus ) in the Region of Waterloo, a highly fragmented agricultural landscape with 14% forest cover in southwestern Ontario. We located 154 Wood Thrush nests and 63 Rose-breasted Grosbeak nests in 26 small forest fragments (3–14 ha) and 15 large fragments (26–140 ha). We used the Mayfield method to determine nesting success. Across all sites nesting success was 51% for Wood Thrushes and 46% for Rose-breasted Grosbeaks. Nesting success and productivity rates were used in a simple population growth model that suggested that the Wood Thrushes but not the Rose-breasted Grosbeaks were a self-sustaining population. Forest size and distance of nests to the nearest forest edge (measured in five distance classes ranging from 0 to over 100 m) did not significantly affect the nesting success or productivity of either species. Brown-headed Cowbirds (   Molothrus ater ) parasitized 47% of all Wood Thrush nests and 10% of all Rose-breasted Grosbeak nests; parasitism significantly reduced Wood Thrush productivity but not that of Rose-breasted Grosbeaks. Our findings challenge the prevailing notion that small woodlots in a farmed landscape are invariably habitat sinks and offer additional incentive for habitat protection in settled landscapes where small forest fragments are often all that remain for conservation purposes.     

Landscape Context Moderates Edge Effects: Nesting Success of Wood Thrushes in Central New York

Abstract:  Despite two decades of research into the effects of habitat fragmentation and edges on nesting birds, critical information about how edges affect the success of natural nests of Neotropical migratory songbirds breeding in heterogeneous landscapes is still missing. We studied abundance and nesting success in Wood Thrushes ( Hylocichla mustelina ) breeding across a heterogeneous landscape in central New York from 1998 to 2000 to test the hypothesis that edge effects on nesting passerines are stronger in fragmented than contiguous landscapes. We monitored nests to estimate nesting success in edge and interior habitats in both fragmented and contiguously forested landscapes. In contiguous landscapes, daily survival rate did not differ between edge nests (0.963) and interior nests (0.968) (χ²= 0.19, p = 0.66). In contrast, in fragmented landscapes, daily survival estimates were higher in interior (0.971) than edge (0.953) nests (χ²= 3.1, p = 0.08). Our study supports the hypothesis that landscape composition moderates edge effects on actual nests of birds but does not determine the mechanisms causing these patterns.     

Extraterritorial Movements of a Forest Songbird in a Fragmented Landscape

Abstract: Forest isolation resulting from fragmentation is thought to impede the movement of forest songbirds. Because of the difficulty of tracking birds continuously, however, few data exist documenting the influence of isolation and landscape features on avian movements. During the breeding season, male Hooded Warblers (    Wilsonia citrina ) leave their small (<2.5 ha), isolated forest patches to travel between forest fragments. We documented a total of 106 forays (  n = 20 males) and found that individuals traveled up to 2.5 km away from their resident forest patch, primarily to solicit covert extra-pair copulations. Forays occurred despite the absence of forested corridors connecting fragments; even when corridors were present, males most often chose to fly directly across open fields. Resident patch size and distance to forests visited were not correlated with the frequency of forays. The maximum distance males flew over open fields did not exceed 465 m, and longer distances likely inhibit males from traveling outside their woodlots. If territorial establishment depends on the availability of extra-pair partners, then higher degrees of isolation between forests could explain why some species avoid settling in extremely fragmented landscapes. Conservation efforts should limit isolation between forest stands, thereby preserving the ability of animals to move within fragmented landscapes during the breeding season.     

Effects of Population Size on Singing Behavior of a Rare Duetting Songbird

Although the genetic and ecological effects of population declines in endangered species have been well studied, little is known of the social consequences. Changes in signaling behavior may result in disrupted communication and affect both reproductive and conflict‐resolution activities. The North Island Kōkako (Callaeas wilsoni) is an endangered, duetting (i.e., alternating, coordinated singing by mated pairs) songbird endemic to New Zealand temperate rain forests. Scattered populations (approximately 1500 individuals in 13 surviving and 11 translocated populations) in isolated conservation areas of different sizes have been rescued from extirpation and are currently recovering. We examined key song attributes of the Kōkako to assess whether population size or growth rate are related to song complexity, the reduction of which may compromise effective communication. We analyzed song repertoire size and phrase‐type sharing (i.e., Jaccard index of similarity), vocal performance (singing rates, song switching rates, and diversity of phrase types), and song syntactical characteristics (i.e., unpredictability in sequences of phrase types) in surviving and translocated populations (populations of approximately 19–250 territorial individuals). Population size was positively correlated with a population's song repertoire, song diversity, and switching of song phrase types and negatively correlated with shared phrase types and variation in syntactical structure of songs. Population growth rate correlated positively with pair repertoire size, population repertoire size, and singing rates during song bouts. As for solo‐singing species in fragmented landscapes, songs in the fragmented populations of Kōkako appear to be undergoing microevolution as occurs in island colonization events. Our results suggest that vocal changes in small populations could affect population establishment and growth, particularly in multiple‐source translocations. We believe measurement of vocal behavior could be used as a supplement to periodic population censuses to allow more frequent monitoring of population size. Efectos de la Conducta de Canto sobre el Tamaño Poblacional de una Ave Canora Rara     

Effects of Exotic Lonicera and Rhamnus on Songbird Nest Predation

Abstract: Habitat fragmentation and disturbance exacerbate the invasion of exotic plant species that, in turn, may attract nesting songbirds by providing a branch structure suitable for nest sites. We document that American Robin ( Turdus migratorius ) nests in two exotic plants, Lonicera maackii and Rhamnus cathartica , experienced higher predation than nests built in comparable native shrubs ( Crataegus, Viburnum ) and native tree species. This was due to a combination of lower nest height, the absence of sharp thorns on the exotic species, and perhaps a branch architecture that facilitated predator movement among the exotic species. In a more subtle interaction, nesting Wood Thrushes ( Hylocichla mustelina ) experienced apparent competition with robins for nest sites in Lonicera , and this interaction was further aggravated by an increased selectivity for Lonicera by nesting robins, possibly due to their early leaf flush and expansion. By documenting increased nest predation in songbirds nesting in exotic shrubs, our results suggest that restoring native plant communities may benefit the surrounding avian community.     

Testing Hypotheses for the Success of Different Conservation Strategies

Abstract:  Evaluations of the success of different conservation strategies are still in their infancy. We used four different measures of project outcomes—ecological, economic, attitudinal, and behavioral—to test hypotheses derived from the assumptions that underlie contemporary conservation solutions. Our hypotheses concerned the effects of natural resource utilization, market integration, decentralization, and community homogeneity on project success. We reviewed the conservation and development literature and used a specific protocol to extract and code the information in a sample of papers. Although our results are by no means conclusive and suffer from the paucity of high-quality data and independent monitoring (80% of the original sample of 124 projects provided inadequate information for use in this study), they show that permitted use of natural resources, market access, and greater community involvement in the conservation project are all important factors for a successful outcome. Without better monitoring schemes in place, it is still impossible to provide a systematic evaluation of how different strategies are best suited to different conservation challenges.     

Assessing Habitat Quality for a Migratory Songbird Wintering in Natural and Agricultural Habitats

Abstract:  As tropical forests are cleared, a greater proportion of migratory songbirds are forced to winter in agricultural and disturbed habitats, which, if poorer in quality than natural forests, could contribute to population declines. We compared demographic indicators of habitat quality for a focal species, the American Redstart ( Setophaga ruticilla ), wintering in Jamaican citrus orchards and shade coffee plantations with those in four natural habitats: mangrove, coastal scrub, coastal palm, and dry limestone forests. Demographic measures of habitat quality included density, age and sex ratio, apparent survival, and changes in body mass. Measures of habitat quality for redstarts in citrus and coffee habitats were generally intermediate between the highest (mangrove) and lowest (dry limestone) measurements from natural habitats. The decline in mean body mass over the winter period was a strong predictor of annual survival rate among habitats, and we suggest that measures of body condition coupled with survival data provide the best measures of habitat quality for nonbreeding songbirds. Density, which is far easier to estimate, was correlated with these more labor-intensive measures, particularly in the late winter when food is likely most limiting. Thus, local density may be useful as an approximation of habitat quality for wintering migrant warblers. Our findings bolster those of previous studies based on bird abundance that suggest arboreal agricultural habitats in the tropics can be useful for the conservation of generalist, insectivorous birds, including many migratory passerines such as redstarts.     

Predicting the Impact of Sea-Level Rise on Caribbean Sea Turtle Nesting Habitat

Abstract:  The projected rise in sea level is likely to increase the vulnerability of coastal zones in the Caribbean, which are already under pressure from a combination of anthropogenic activities and natural processes. One of the major effects will be a loss of beach habitat, which provides nesting sites for endangered sea turtles. To assess the potential impacts of sea-level rise on sea turtle nesting habitat, we used beach profile measurements of turtle nesting beaches on Bonaire, Netherlands Antilles, to develop elevation models of individual beaches in a geographic information system. These models were then used to quantify areas of beach vulnerable to three different scenarios of a rise in sea level. Physical characteristics of the beaches were also recorded and related to beach vulnerability, flooding, and nesting frequency. Beaches varied in physical characteristics and therefore in their vulnerability to flooding. Up to 32% of the total current beach area could be lost with a 0.5-m rise in sea level, with lower, narrower beaches being the most vulnerable. Vulnerability varied with land use adjacent to the beach. These predictions about loss of nesting habitat have important implications for turtle populations in the region.