Latitudinal differences in timing of breeding are well documented but how such differences carry over to influence timing of events in the annual cycle of migratory birds is not well understood. We examined geographical variation in timing of events throughout the year using light-level geolocator tracking data from 133 migratory tree swallows ( Tachycineta bicolor ) originating from 12 North American breeding populations. A swallow's breeding latitude influenced timing of breeding, which then carried over to affect breeding ground departure. This resulted in subsequent effects on the arrival and departure schedules at autumn stopover locations and timing of arrival at non-breeding locations. This ‘domino effect’ between timing events was no longer apparent by the time individuals departed for spring migration. Our range-wide analysis demonstrates the lasting impact breeding latitude can have on migration schedules but also highlights how such timing relationships can reset when individuals reside at non-breeding sites for extended periods of time.

Determining how migratory animals are spatially connected between breeding and non‐breeding periods is essential for predicting the effects of environmental change and for developing optimal conservation strategies. Yet, despite recent advances in tracking technology, we lack comprehensive information on the spatial structure of migratory networks across a species’ range, particularly for small‐bodied, long‐distance migratory animals. We constructed a migratory network for a songbird and used network‐based metrics to characterize the spatial structure and prioritize regions for conservation. The network was constructed using year‐round movements derived from 133 archival light‐level geolocators attached to Tree Swallows (Tachycineta bicolor) originating from 12 breeding sites across their North American breeding range. From these breeding sites, we identified 10 autumn stopover nodes (regions) in North America, 13 non‐breeding nodes located around the Gulf of Mexico, Mexico, Florida, and the Caribbean, and 136 unique edges (migratory routes) connecting nodes. We found strong migratory connectivity between breeding and autumn stopover sites and moderate migratory connectivity between the breeding and non‐breeding sites. We identified three distinct “communities” of nodes that corresponded to western, central, and eastern North American flyways. Several regions were important for maintaining network connectivity, with South Florida and Louisiana as the top ranked non‐breeding nodes and the Midwest as the top ranked stopover node. We show that migratory songbird networks can have both a high degree of mixing between seasons yet still show regionally distinct migratory flyways. Such information will be crucial for accurately predicting factors that limit and regulate migratory songbirds throughout the annual cycle. Our study highlights how network‐based metrics can be valuable for identifying overall network structure and prioritizing specific regions within a network for conserving a wide variety of migratory animals.

Determining the distribution of stopover and overwintering areas of migratory animals is essential for understanding population dynamics and building predictive models. Tree Swallows (Tachycineta bicolor) are small songbirds that breed across North America. Data from Doppler weather radar and eBird indicate that Tree Swallow numbers increase throughout October and November in southeastern Louisiana, but then decrease during December. We thus hypothesized that southeastern Louisiana is a stopover area used by Tree Swallows during fall migration before they move to farther overwintering areas. We tested this hypothesis by attaching light-logging geolocators to Tree Swallows at five breeding sites spanning the species' breeding range from British Columbia to Nova Scotia, and then tracking their fall migration routes, stopover sites, and wintering locations. Of 38 individuals that returned in the following breeding season, 11 birds from three breeding sites (Saskatchewan, Wisconsin, and Ontario) used southeastern Louisiana as a stopover site. Arrival date and duration of stay closely matched observations from both eBird and radar data. From Louisiana, most Tree Swallows continued their migration to one of three wintering sites: peninsular Florida, the Bahamas, or the Yucatán Peninsula, whereas two birds remained until spring within 200 km of the stopover area. Our results (1) suggest that southeastern Louisiana is an extended stopover site for Tree Swallows that originate from a wide geographic range on the breeding grounds; and (2) demonstrate how geolocators, combined with other sources of movement information, reveal habitat use throughout the annual cycle.

Our understanding of the annual life-cycle movements of small migratory birds has 1 advanced rapidly with the advent of light-weight geographical positioning devices (i.e., 2 geolocators), yet the effects of geolocators on reproduction and survival have not been 3 adequately quantified. We tested for impacts of attaching a 1g geolocator (using a harness 4 around the legs and back, anterior to the tail) to adult Tree Swallows (Tachycineta bicolor) on 5 parental feeding behaviour, nestling growth and size, fledging success, and return rates 6 between 2011-2012. At one breeding site, we compared feeding visits, nestling growth, and 7 nestling size between paired nest boxes where one parent was marked at the 'geolocator' box 8 with a 'control' nest box where neither parent was marked. We detected no differences 9 between geolocator and control nests in either the frequency of feeding visits to nestlings or 10 the amount of time spent at nests. Birds marked with geolocators fed nestlings as frequently 11 as their unmarked mates. Likewise, nestlings raised at geolocator nests grew at similar rates 12 to those at control nests, and had similar structural size and body mass at fledging. At three 13 widely-separated sites across the Tree Swallow breeding range in Canada, we also found that 14 fledging success was similar for geolocator and control nests. Although we found no 15 evidence for short-term negative impacts of geolocators, the return rates of geolocator-16 marked swallows tended to be significantly lower than those of unmarked control birds. 17Thus, we found little evidence for short-term impacts of geolocators on reproduction but our 18 study does suggest that long-term impacts of geolocators could be manifested in terms of 19 lower survival, higher emigration rates, or lower breeding propensity.

Vocal communication in duetting and chorusing birds is a growing area of study in avian ecology, yet much remains unknown about temporal and population-level variation in these complex vocal signals. In this study, we describe the acoustic structure and temporal variation in solos, duets, and choruses in the Rufous-naped Wren (Campylorhynchus rufinucha), a cooperatively breeding neotropical passerine. We collected focal recordings of 19 groups to assess both diel and seasonal variation in vocal output, as well as population-wide sharing of vocal signals. We found that birds produce a complex array of vocalisations, including tonal, frequency-modulated syllables grouped into phrases, as well as stereotyped, atonal sounds. Songs are produced as solos or combined into duets and choruses. Solo and duet songs show a dawn chorus effect. Solo song rate, but not duet or chorus rate, varied across breeding stages. The majority of phrases are shared amongst groups, significantly more amongst groups in nearby territories. We suggest that chorus songs may be an important indicator of group identity and may play a role in maintaining group territories, but do not play a role in relation to the breeding cycle. The degree of population-wide phrasesharing suggests either short-distance dispersal or delayed song learning. This paper is the first fine-scale description of vocal behaviour in this species and enhances our understanding of group-singing in a complex social environment.

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Despite benefits of using light-sensitive geolocators to track animal movements and describe patterns of migratory connectivity, concerns have been raised about negative effects of these devices, particularly in small species of aerial insectivore. Geolocators may act as handicaps that increase energetic expenditure, which could explain reported effects of geolocators on survival. We tested this ‘Energetic Expenditure Hypothesis’ in 12 populations of tree swallows (Tachycineta bicolor) and barn swallows (Hirundo rustica) from North America and Europe, using measurements of corticosterone from feathers (CORTf) grown after deployment of geolocators as a measure of physiology relevant to energetics. Contrary to predictions, neither among- (both species) nor within-individual (tree swallows only) levels of CORTf differed with respect to instrumentation. Thus, to the extent that CORTf reflects energetic expenditure, geolocators apparently were not a strong handicap for birds that returned post-deployment. While this physiological evidence suggests that information about migration obtained from returning geolocator-equipped swallows is unbiased with regard to levels of stress, we cannot discount the possibility that corticosterone played a role in reported effects of geolocators on survival in birds, and suggest that future studies relate corticosterone to antecedent factors, such as reproductive history, and to downstream fitness costs.

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