Widespread population declines of the Golden-winged Warbler (Vermivora chrysoptera) are thought to be due in part to hybridization with the expanding Blue-winged Warbler (V. pinus), which predictably replaces Golden-winged Warblers at breeding sites in which the two species come into contact. However, the mechanism by which this replacement occurs remains unresolved. Recent genetic work has indicated that, even in areas where the two species have been in contact for a short period, introgression of Blue-winged mitochondrial (mtDNA) and nuclear genes into Golden-winged individuals is common. To explore this process on a broader scale, we screened more than 750 individuals from nine U.S. states and three provinces to examine geographic patterns of mtDNA introgression. The only population in which all phenotypic Golden-winged Warblers had Golden-winged mtDNA haplotypes, and in which there are no breeding Blue-winged or hybrid individuals, was in the province of Manitoba, near the northwestern edge of the species' breeding distribution. The near ubiquity of mitochondrial introgression suggests that there are far fewer genetically pure populations of Goldenwinged Warblers than previously believed, a finding with important implications for this threatened species. RÉSUMÉ. On pense que le déclin à grande échelle des populations de Paruline à ailes dorées (Vermivora chrysoptera) est en partie attribuable à son hybridation avec la Paruline à ailes bleues (V. pinus), laquelle est en expansion et remplace, comme on peut s'y attendre, la Paruline à ailes dorées aux sites de nidification où les deux espèces entrent en contact. Toutefois, le processus par lequel survient ce remplacement demeure inconnu. Des études génétiques récentes ont montré que, même aux endroits où les deux espèces n'ont été en contact que sur une courte période, l'introgression des gènes mitochondriaux (ADNmt) et nucléaires de la Paruline à ailes bleues chez les individus de Paruline à ailes dorées est commune. Pour explorer ce processus à plus grande échelle, nous avons procédé au criblage de plus de 750 individus provenant de neufs États des États-Unis et de trois provinces afin d'examiner les variations géographiques de l'introgression mitochondriale. La seule population dans laquelle toutes les Parulines à ailes dorées phénotypiques présentaient des haplotypes d'ADNmt de Paruline à ailes dorées, et dans laquelle il n'y avait pas d'individus nicheurs de Paruline à ailes bleues ni d'hybrides, se trouvait au Manitoba, près de la limite nord-ouest de l'aire de reproduction de l'espèce. La quasiomniprésence de l'introgression mitochondriale permet de croire qu'il y a beaucoup moins de populations génétiquement pures de Paruline à ailes dorées que ce qu'on pensait, une découverte significative pour cette espèce menacée.
Forest cover in the eastern United States has increased over the past century and while some late-successional species have benefited from this process as expected, others have experienced population declines. These declines may be in part related to contemporary reductions in small-scale forest interior disturbances such as fire, windthrow, and treefalls. To mitigate the negative impacts of disturbance alteration and suppression on some late-successional species, strategies that emulate natural disturbance regimes are often advocated, but large-scale evaluations of these practices are rare. Here, we assessed the consequences of experimental disturbance (using partial timber harvest) on a severely declining late-successional species, the cerulean warbler (Setophaga cerulea), across the core of its breeding range in the Appalachian Mountains. We measured numerical (density), physiological (body condition), and demographic (age structure and reproduction) responses to three levels of disturbance and explored the potential impacts of disturbance on source-sink dynamics. Breeding densities of warblers increased one to four years after all canopy disturbances (vs. controls) and males occupying territories on treatment plots were in better condition than those on control plots. However, these beneficial effects of disturbance did not correspond to improvements in reproduction; nest success was lower on all treatment plots than on control plots in the southern region and marginally lower on light disturbance plots in the northern region. Our data suggest that only habitats in the southern region acted as sources, and interior disturbances in this region have the potential to create ecological traps at a local scale, but sources when viewed at broader scales. Thus, cerulean warblers would likely benefit from management that strikes a landscape-level balance between emulating natural disturbances in order to attract individuals into areas where current structure is inappropriate, and limiting anthropogenic disturbance in forests that already possess appropriate structural attributes in order to maintain maximum productivity.
ABSTRACT. Among shrubland-and young forest-nesting bird species in North America, Golden-winged Warblers (Vermivora chrysoptera) are one of the most rapidly declining partly because of limited nesting habitat. Creation and management of high quality vegetation communities used for nesting are needed to reduce declines. Thus, we examined whether common characteristics could be managed across much of the Golden-winged Warbler's breeding range to increase daily survival rate (DSR) of nests. We monitored 388 nests on 62 sites throughout Minnesota, Wisconsin, New York, North Carolina, Pennsylvania, Tennessee, and West Virginia. We evaluated competing DSR models in spatial-temporal (dominant vegetation type, population segment, state, and year), intraseasonal (nest stage and time-within-season), and vegetation model suites. The best-supported DSR models among the three model suites suggested potential associations between daily survival rate of nests and state, time-within-season, percent grass and Rubus cover within 1 m of the nest, and distance to later successional forest edge. Overall, grass cover (negative association with DSR above 50%) and Rubus cover (DSR lowest at about 30%) within 1 m of the nest and distance to later successional forest edge (negative association with DSR) may represent common management targets across our states for increasing Golden-winged Warbler DSR, particularly in the Appalachian Mountains population segment. Context-specific adjustments to management strategies, such as in wetlands or areas of overlap with Blue-winged Warblers (Vermivora cyanoptera), may be necessary to increase DSR for Golden-winged Warblers. Variables associées à la survie des nids de Paruline à ailes dorées (Vermivora chrysoptera) parmi les communautés végétales fréquemment utilisées pour nicherRÉSUMÉ. Parmi les espèces d'oiseaux d'Amérique du Nord qui nichent dans les milieux arbustifs et les jeunes forêts, la Paruline à ailes dorées (Vermivora chrysoptera) est l'une de celles dont les populations diminuent le plus rapidement en raison du peu de milieux de nidification. Afin de freiner cette baisse, la création et l'aménagement de communautés végétales de qualité sont nécessaires pour la nidification de l'espèce. Nous avons examiné s'il était possible d'aménager sur la base de caractéristiques communes dans une grande partie de l'aire de reproduction de cette paruline pour augmenter le taux de survie quotidien des nids (TSQ). Nous avons suivi 388 nids dans 62 stations réparties au Minnesota, au Wisconsin, dans l'État de New York, en Caroline du Nord, en Pennsylvanie, au Tennessee et en Virginie occidentale. Nous avons évalué trois séries de modèles de TSQ fondés sur les caractéristiques spatio-temporelles (type de végétation dominante, segment de la population, État et année), intrasaisonnières (stade du nid et moment durant la saison) et végétales. Parmi tous les modèles, les meilleurs montraient une association potentielle du taux de survie quotidien des nids avec l'État, le moment durant la saison, le pourcent...
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