Nest-site characteristics and breeding success of three species of boreal songbirds in western Newfoundland, Canada

Delineating habitat requirements and preferences of species is essential for conservation planning. We studied nest habitat use and effects of microsite vegetation characteristics on breeding success of yellow-rumped warblers ( Dendroica coronata (L., 1766)), blackpoll warblers ( Dendroica striata (J.R. Forster, 1772)), and white-throated sparrows ( Zonotrichia albicollis (Gmelin, 1789)) in an area with a low extent (<6% of available land) of forest harvest in northwestern Newfoundland. During 2004 and 2005, 99 nests were located and monitored, and the characteristics of nest sites measured. Vegetation at yellow-rumped and blackpoll warbler nest sites differed from random sites; however, within used sites, no vegetation characteristics were significantly associated with success. White-throated sparrow nest sites contained more downed wood and less ground vegetation than did random sites; however, successful nests were associated with different variables than those that distinguished them from random sites, including less canopy cover and less woody debris. Thus, whereas yellow-rumped and blackpoll warblers used specific nest-site characteristics and white-throated sparrows had higher nest success associated with certain characteristics, the nest characteristics these birds appeared to choose did not have demonstrable fitness benefits.

Autumn stopover ecology of the Blackpoll Warbler (Dendroica striata) in thorn scrub forest of the Dominican Republic

We used mist-netting, color-banding, resighting, and behavioral observations to study the autumn stopover ecology of migrating Blackpoll Warblers (Dendroica striata) in coastal thorn scrub forest in the area of Cabo Rojo, Pedernales Province, Dominican Republic. Blackpoll Warblers were the most abundant migrant present in this habitat throughout most of October 1997. Warblers stopping over in this habitat were generally young with moderate to large fat stores. No lean birds (fat score = 0) were captured. Our behavioral observations suggest that Blackpoll Warblers are flexible in terms of social organization, with birds associating in single-species flocks and in mixed-species aggregations, but single birds were also recorded. Foraging activity consisted primarily of gleaning from leaves and was focused on lepidopteran larvae, whose high abundance coincided with Blackpoll Warbler arrival. We suggest that most stopover Blackpoll Warblers were not weakened individuals searching for emergency energy stores but were forced down owing to unfavorable weather conditions for migration; others may have been taking advantage of landfall on the south coast of Hispaniola for daytime rest before continuing across the Caribbean Sea to South America. Coastal thorn scrub forest of Hispaniola appears to be a preferred stopover habitat for a variety of migrants, providing a place to rest and replenish energy reserves following transoceanic flight.

Female Site Fidelity and Polygyny in the Blackpoll Warbler (Dendroica Striata)

From 1980 to 1982, 8-30% of male Blackpoll Warblers (Dendroica striata) studied on Kent Island, New Brunswick, were bigamous each year (x̄ = 16.8%). I tested whether differences in the quality of the breeding situation can give rise to polygynous matings. Five territory parameters and two male parameters were used as measures of quality. Male arrival times were correlated with male mating status and the reproductive success of monogamous females. Territories of bigamous males had more large conifers than did those of monogamous males. Territory parameters did not appear to influence female choices. Strong site attachment by females may lead them to mate bigamously when few males are available early in the season near the females' former nest sites. The reproductive success of secondary females was not different from that of monogamous females. Any costs of mating bigamously may be offset by increased reproductive success associated with early nest initiation and competitive advantages conferred by site dominance. Site attachment and return patterns can account for the incidence of polygyny in this population, but probably could not give rise to high levels of polygyny or large harems. More information is needed to evaluate the influence of site fidelity on mating decisions of females in other polygynous passerine species.