Summary 1.To minimize study-area artefacts in a study of natal dispersal distances in tree swallows, we intensively banded nestlings and adults in nest-boxes in upstate New York and recruited and trained 70 volunteer banders within a 400 km radius of Ithaca. We banded 26 567 nestlings in the years 1985 through 1998, and captured 4774 adults at the nest, 630 of which had been banded as nestlings and were recaptured the year after fledging. 2. To correct for spatial variation in capture intensity, we resampled the distribution of all boxes where an adult capture was made under uniform, exponential and Cauchy null hypotheses. Compared to the null distributions, the frequency of observed dispersal events was significantly higher at 0 -10 km and lower for all larger dispersal distances. The Cauchy distribution came closest to approximating the observed dispersal distance distribution. 3. Dispersal distances were sensitive to the distribution of nesting sites, and all measurements of dispersal distance distributions must be seen as being habitat-specific. We could detect no effect of dispersal distance on the subsequent timing of breeding and no effect of the timing of fledging on dispersal distance. The sexual differences in raw mean dispersal distances (8·38 km for females, 2·44 km for males) are similar to those reported for other species. 4. While it is tempting to conclude that studies in smaller areas have not missed a great deal, even a study area of 10 km extent (substantially larger than most) would have missed 11% of the dispersing birds detected and 95% of the range of distances recorded. Despite this sizeable component that would have been missed with a smaller study area, the relatively low frequencies of long-distance dispersal overall reinforce the conclusion that tree swallows, and probably most other migratory passerines, generally disperse much less far from their natal sites than the distances of their annual migrations might lead one to expect.

To study the patterns and determinants of philopatry and breeding dispersal in the Tree Swallow (Tachycineta bicolor) we analyzed the records of 356 males and 1459 females captured in more than one breeding year around Ithaca, New York. Of these captures, only 4% of male and 14% of female breeders dispersed to a new site for breeding. With our combination of intensive study areas in Tompkins County, New York, and the efforts of volunteer banders throughout New York and surrounding states, we could have detected dispersal in excess of 400 km from the initial breeding site. Randomization tests revealed, however, that breeders dispersed much shorter distances than they could have been detected. Detailed analyses of recaptures in Tompkins County showed that over a 22-km range of distances, the chances of dispersal to a new breeding site declined with the distance from the original breeding site. Females that failed to fledge any offspring were much more likely to disperse than females that reproduced successfully, and the probability of dispersal declined gradually with female age. The spatial scale in which swallows gather and process information appears to be much larger than for passerines that defend all-purpose territories.Dispersión Reproductiva y Filopatría en Tachycineta bicolorResumen. Para estudiar los patrones y los determinantes de la filopatría y la dispersión reproductiva en Tachycineta bicolor analizamos los registros de 356 machos y 1459 hembras capturados en más de un año reproductivo en los alrededores de Ithaca, New York. De estas capturas, sólo el 4% de los machos y el 14% de las hembras reproductivas se dispersaron a un nuevo sitio de cría. Con nuestra combinación de áreas de estudio intensivas en el Condado de Tompkins, New York, y los esfuerzos de colaboradores voluntarios que anillaron aves a lo largo de New York y los estados circundantes, pudimos haber detectado eventos de dispersión a más de 400 km desde el sitio de cría inicial. Exámenes aleatorizados revelaron, sin embargo, que las aves reproductivas se dispersaron a distancias mucho más cortas que las que se podrían haber detectado. Análisis detallados de recapturas en el Condado de Tompkins mostraron que en un rango de distancias de 22 km, las probabilidades de dispersión a un nuevo sitio de cría disminuyeron con la distancia desde el sitio de cría original. Las hembras que fracasaron en la cría de pichones presentaron una probabilidad de dispersarse mucho mayor que las hembras que se reprodujeron exitosamente, y la probabilidad de dispersión disminuyó gradualmente con la edad de la hembra. La escala espacial a la que T. bicolor recoge y procesa información parece ser mucho más grande que la de aves paserinas que defienden territorios de uso múltiple.

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The seasonal pattern of clutch size variation in birds varies among species. In single‐brooded bird species clutch sizes decline continuously with date from an early season maximum. In resident multi‐brooded species, clutch sizes first increase to a mid‐season maximum and then decrease again. Limited data for multi‐brooded migratory birds suggest that clutches in these species also show a continuous decline throughout the season, but it remains to be resolved whether this applies generally and whether migration adds a constraint to the system. We here report on a study of the Eastern Bluebird Sialia sialis conducted using data collected by volunteers across most of its range. In the southern part of its range, where Eastern Bluebirds are largely year‐round residents, clutches initially increase, reach a mid‐season maximum and gradually decline later in the season. In the northern part of the range, where the majority of Eastern Bluebirds are migratory, clutch sizes decline continuously throughout the season. To determine whether seasonal changes in the clutch size of multi‐brooded species are determined by migratory behaviour of the population we compared our results with published data on the Dunnock Prunella modularis and conclude that in multi‐brooded species migratory behaviour is not a sufficient condition for a continuous seasonal decline in clutch size, but it could be a necessary one. We propose two mechanisms for the pattern observed among multi‐brooded migrants: (i) a time or energy cost of migration, and (ii) a more abrupt increase in seasonal resources in spring at more northerly latitudes.

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