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Effects of breeding and molt activity on songbird site fidelity
Abstract
The prebasic molt is a perilous period for songbirds, characterized by heightened energetic demands and vulnerability to predators. Given these vulnerabilities, songbirds are under selective pressure to locate and use quality habitat during the prebasic molt, potentially resulting in site fidelity between years. In this study, we aimed to determine how differences in breeding and molting activity affected site fidelity for a diversity of species at the landscape scale. To accomplish our
objective, we used 31 yr of banding data from northern California and southern Oregon for 16 species of songbirds with Cormack-Jolly-Seber analyses and weighted linear regression models to assess the effects of molting and breeding activity on the probability of a species returning to a site in subsequent years. Despite substantial variation in site use for breeding and/or molting, each study species had at least some locations that were used for both breeding and molting. Captured breeding birds (n = 18,574) were much more common than molting birds (n = 7,622). Breeding activity was
positively correlated with higher site fidelity for 10 of the 16 species, while we found little evidence of a relationship between molting activity and site fidelity. Only the Dark-eyed Junco (Junco hyemalis) showed increased site fidelity with increased presence of molt activity. It is likely that a shifting mosaic of food resources during the post-breeding period drives dynamic movements of songbirds in search of the necessary resources to successfully complete their annual molt.
... Few studies have investigated causes of variation. For example, while other activities could also be drivers of site fidelity, effects of moult activity were only found in one out of 16 species of songbirds (dark-eyed junco Junco hyemalis; Figueira et al. 2020). ...
Most migratory birds return every year to the same breeding sites and some species show a similarly high fidelity to wintering grounds as well. Fidelity to stopover sites during migration has been much less studied and is usually found to be lower. Here, we investigate site fidelity and distance to previously visited sites throughout the annual cycle in the common cuckoo, a nocturnal trans‐Saharan migrant, based on satellite‐tracking data from repeated annual migrations of thirteen adult males. All birds (100%) returned to the same breeding grounds, with a median shortest distance of only 1 km from the locations in previous year. This was in strong contrast to a much lower and much less precise site fidelity at non‐breeding sites during the annual cycle: In only 18% of the possible cases in all non‐breeding regions combined, did the cuckoos return to within 50 km of a previously visited non‐breeding site, with no significant differences among the main staging regions (Europe in autumn, Sahel in autumn, wintering in Central Africa, West Africa in spring, Europe in spring). The shortest distance to a previously visited non‐breeding site differed among the staging regions with median shortest distances for the longest stopovers of 131 km [2;1223] (median [min;max]) in Europe, 207 km [1;2222] in Sahel in autumn and 110 km [0;628] in Central Africa. The distance to a previously visited staging site decreased with the time spent at the stopover in a previous year. Understanding the drivers of recurrence and site selection in migratory birds are important for guiding conservation efforts in this group but further studies are needed to establish whether the patterns observed in cuckoos are general among terrestrial migrants with continuous distribution of habitat.
Fidelity of individual shorebirds to stopover sites between years has been documented in only a few species. In May 2005, we recaptured a migrant male Western Sandpiper (Calidris mauri) on the Copper River Delta, Alaska, 5.8 km from its original 2004 capture site. We classified the individual as a first-year bird in 2004 and as an adult in 2005. This report extends our knowledge of site fidelity in migrant shorebirds to one of the most common species on the west coast of North America, and to a small geographic area within a larger stopover site.
To avoid energy allocation conflicts, birds generally separate breeding, migration and moult during the annual cycle. North American passerines typically moult on the breeding grounds prior to autumn migration. However, some have evolved a moult-migration strategy in which they delay moult until stopping over during autumn migration. Rohwer et al. (2005) proposed the 'push-pull hypothesis' as an explanation for the evolution of this moult strategy, but it has not been empirically tested. Poor conditions on the breeding grounds at the end of the summer would push birds to depart prior to moult, while productive stopover locations would pull them. We tested for a relationship between moult-migration and breeding grounds aridity as measured by the normalized difference vegetation index. Our results strongly support the 'push' aspect of the push-pull hypothesis and indicate that arid breeding grounds, primarily in western North America, would drive species to evolve stopover moult-migration, although this relationship may depend upon migration distance.
Intraspecific patterns of autumn migration timing are not well known, particularly in the western United States. Here, we (1) describe autumn migration timing and age ratios of landbird migrants in southwestern Idaho, (2) examine differences in timing among age and sex classes, and (3) demonstrate how prebasic molt strategies affect migration timing differences between age classes. As a group, Neotropical migrants were most common from late July through early September, whereas temperate migrants were most common from mid-September into early October. Proportion of hatch-year birds was 74.5% for all migrants combined and ranged from 33.3% to 100% for individual species. Timing differences between sex classes were detected in only a few species and no general patterns emerged. In 22 of 31 Neotropical and temperate migrants examined, there were significant differences in timing between adults and hatch-year birds. In species in which adults begin fall migration before replacing flight feathers, adults migrated earlier than hatch-year birds. Conversely, in species in which adults molt flight feathers on or near the breeding grounds before departing on fall migration, hatch-year birds migrated earlier than adults in all but one case. Therefore, it appears that molt strategy is a powerful determinant of intraspecific migration timing differences and, to our knowledge, this is the first study to document this pattern among migrant passerines of North America.
Estrategias de Muda y Diferencias en el Momento de Migración Otoñal en Migrantes Terrestres en el Suroeste de Idaho
We studied three Nearctic migrant species (American Redstart [Setophaga ruticilla], AMRE; Black-and-white Warbler [Mniotilta varia], BAWW; Black-throated Blue Warbler [Dendroica caerulescens ], BTBW) wintering in 14 isolated shade coffee plantations (0.1 to 8.7 ha) in the Dominican Republic to determine if site fidelity was comparable to that in tropical forests and if it decreased with plantation size. Site fidelity was measured as the percentage of wandering birds captured in mist nets, as overwinter site persistence of uniquely marked birds observed on the same sites (November to March), and as annual return of marked individuals to previously occupied sites (January to January). The percentages of wanderers in net captures were mostly lower than values reported for natural forests (AMRE 21%, BAWW 12%, BTBW 41%) and did not vary with plantation size. Overwinter site persistence (AMRE 65%, BAWW 65%, BTBW 76%) and annual return (AMRE 34%, BAWW 40%, BTBW 31%) in the plantations fell within the range of values reported for natural forests. Overwinter site persistence decreased with plantation size only in AMRE, although BAWW showed lower persistence in small plantations from early to midwinter. Annual return decreased with plantation size only in AMRE. Despite diminished site fidelity in small plantations, these birds showed some fidelity to small plantations, many of which were smaller than the mean size of winter home ranges.
The occurrence of molt during migration, known as "molt-migration," has increasingly received attention across many avian taxa since first being described in waterfowl in the 1960s. However, despite the many different types of molt stages and strategies, most, if not all, uses of the term "molt-migration" apply to the definitive prebasic molt of flight feathers in post-breeding adults, whereas fewer studies address migration for body-feather molts. Here, we argue that the current definition of molt-migration, as applied, is limited in focus relative to the diverse ways in which it can manifest in avian populations. We suggest a new, broader definition of molt-migration and highlight examples of molt-migration as traditionally defined, and the many examples that have not been defined as such. We propose a new, 2-tiered typology for defining different forms of molt-migration, based on (1) its progression relative to stationary portions of the annual cycle, and (2) the stage of molt involved. In order to advance our understanding of the ecology and evolution of this increasingly documented phenomenon and apply this knowledge to conservation and management, avian researchers must begin to utilize a common framework for describing molt-migration in its various forms.
During migration, birds require stopover habitat to rest and refuel before resuming flight. While long-distance
migratory flights represent a large energy investment, stopover accounts for roughly two-thirds of a bird’s total
energy expenditure during migration. Therefore, birds should minimize energy expenditure while also minimizing
time and predation risk during stopover. To understand activity during migration, we recorded activity patterns (i.e.
fine-scale movements associated with a range of behaviors) of 3 species, Red-eyed Vireo (Vireo olivaceus), Swainson’s
Thrush (Catharus ustulatus), and Wood Thrush (Hylocichla mustelina), at a stopover site along the northern coast of
the Gulf of Mexico during autumn migration using automated radio telemetry. We found Red-eyed Vireos to be the
most active and Swainson’s Thrushes the least active. For each species, we used boosted regression trees to
investigate associations between activity and factors known to influence bird behavior during stopover. While
species differed, day of year and temperature were important predictors of activity for all species. Vireos were active
early in the season, under light winds and warmer temperatures, and on evenings when winds were more favorable.
Thrushes were more active as the season progressed and when temperatures were cooler. Thrush activity also
differed between years, although thrushes passed through the site later in the season during all years. Our results
illustrate automated radio telemetry as a unique and valuable tool for understanding fine-scale behaviors of birds
during stopover.
Animal migration has been the subject of intensive research for more than a century, but most research has focused on long‐distance rather than short‐distance migration. Altitudinal migration is a form of short‐distance migration in which individuals perform seasonal elevational movements. Despite its geographic and taxonomic ubiquity, there is relatively little information about the intrinsic and extrinsic factors that influence altitudinal migratory behaviour. Without this information, it is difficult to predict how rapid environmental changes will affect population viability of altitudinal migrants. To synthesize current knowledge, we compiled literature on altitudinal migration for all studied taxa, and identified the leading hypotheses explaining this behaviour. Studies of animal altitudinal migration cover many taxonomic lineages, with birds being the most commonly studied group. Altitudinal migration occurs in all continents except for Antarctica, but about a third of the literature focused on altitudinal migration in North America. Most research suggests that food and weather are the primary extrinsic drivers of altitudinal migration. In addition, substantial individual‐level variation in migratory propensity exists. Individual characteristics that are associated with sex, dominance rank, and body size explain much of the variation in migratory propensity in partially migratory populations, but individual‐level correlates are poorly known for most taxa. More research is needed to quantify the effects of habitat loss, habitat fragmentation, and climate change on altitudinal migrants. Demographic studies of individually marked populations would be particularly valuable for advancing knowledge of the cascading effects of environmental change on migratory propensity, movement patterns, and population viability. We conclude our review with recommendations for study designs and modelling approaches that could be used to narrow existing knowledge gaps, which currently hinder effective conservation of altitudinal migratory species.
Migratory birds spend most of their journeys at stopover sites where they rest and refuel. Many migrants are in steep decline, and understanding their behavior within and among migrations is crucial for developing effective conservation strategies across the full annual cycle. One of the most rapidly declining songbirds in North America is the Rusty Blackbird (Euphagus carolinus; 85-95% decline over the past 50 yr), and stopover ecology is a major gap in our knowledge of its annual cycle. We utilized an automated telemetry array in western Lake Erie and the Motus Wildlife Tracking System to track landscape-scale movements, stopover duration, departure behavior, and between-season site fidelity in this species. We found that stopover duration during both fall and spring was nearly 1 mo (mean = 25.5 days)-exceptionally long for a passerine. During spring, birds in both poor condition and high degree of molt had longer stopovers, post-departure flights were relatively long for a songbird, and tailwinds predicted departure in both seasons. Many individuals made landscape-scale (10-35 km) relocations during stopover. Site fidelity was high for a passerine, in terms of both route and stopover site. Taken together, these behaviors describe a migration strategy that largely matches the staging behavior of shorebirds. Lastly, we found that Rusty Blackbirds migrate directly across Lake Erie and migrate primarily at night, which might expose them to mortality from offshore wind development. Collectively, our results indicate that high-quality stopover habitat may be critically important to Rusty Blackbird populations. More broadly, our results highlight the need to expand the scale of stopover studies, and to further explore all aspects of species' annual cycles to understand potential limiting factors on populations.
Migratory species employ a variety of strategies to meet energetic demands of postbreeding molt. As such, at least a few species of western Neotropical migrants are known to undergo short-distance upslope movements to locations where adults molt body and flight feathers (altitudinal molt migration). Given inherent difficulties in measuring subtle movements of birds occurring in western mountains, we believe that altitudinal molt migration may be a common yet poorly documented phenomenon. To examine prevalence of altitudinal molt migration, we used 29 years of bird capture data in a series of linear mixed-effect models for nine commonly captured species that breed in northern California and southern Oregon. Candidate models were formulated a priori to examine whether elevation and distance from the coast can be used to predict abundance of breeding and molting birds. Our results suggest that long-distance migrants such as Orange-crowned Warbler (Oreothlypis celata) moved higher in elevation and Audubon's Warbler (Setophaga coronata) moved farther inland to molt after breeding. Conversely, for resident and short-distance migrants, we found evidence that birds either remained on the breeding grounds until they finished molting, such as Song Sparrow (Melospiza melodia) or made small downslope movements, such as American Robin (Turdus migratorius). We conclude that altitudinal molt migration may be a common, variable, and complex behavior among western songbird communities and is related to other aspects of a species’ natural history, such as migratory strategy.
Untangling the spatial and temporal processes that influence population dynamics of migratory species is challenging, because changes in abundance are shaped by variation in vital rates across heterogeneous habitats and throughout the annual cycle. We developed a full-annual-cycle, integrated population model and used demographic data collected between 2011 and 2014 in southern Indiana and Belize to estimate stage-specific vital rates of a declining migratory songbird, the Wood Thrush (Hylocichla mustelina). Our primary objective was to understand how spatial and temporal variation in demography contributes to local and regional population growth. Our full-annual-cycle model allowed us to estimate: 1) age-specific, seasonal survival probabilities, including latent survival during both spring and autumn migration, and 2) how the relative contribution of vital rates to population growth differed among habitats. Wood Thrushes in our study populations experienced the lowest apparent survival rates during migration and apparent survival was lower during spring migration than during fall migration. Both mortality and high dispersal likely contributed to low apparent survival during spring migration. Population growth in high-quality habitat was most sensitive to variation in fecundity and apparent survival of juveniles during spring migration, whereas population growth in low-quality sites was most sensitive to adult apparent breeding-season survival. These results elucidate how full-annual-cycle vital rates, particularly apparent survival during migration, interact with spatial variation in habitat quality to influence population dynamics in migratory species.
Altitudinal bird migration involves annual seasonal movements up and down elevational gradients. Despite the fact that species from montane avifaunas worldwide engage in altitudinal migration, the patterns, causes, and prevalence of these movements are poorly understood. This is particularly true in North America where the overwhelming majority of avian migration research has focused on obligate, long-distance, temperate–tropical movements. Elsewhere in the world, most altitudinal migrants are partial migrants, making downhill movements to nonbreeding areas. However, spatial and temporal patterns, the prevalence and predictability of migration at individual and population levels, and the ultimate ecological factors selecting for movement behavior vary considerably among taxa and regions. I conducted a systematic survey of the evidence for altitudinal migration to fill gaps in our understanding of this behavior among the landbirds of North America and Hawaii. Altitudinal migration was as prevalent as in other avifaunas, occurring in >20% of continental North American and nearly 30% of Hawaiian species. Of the species wintering within the USA and Canada, ∼30% engage in altitudinal migrations. Altitudinal migrants are far more common in the West, are taxonomically and ecologically diverse, and North American species exhibit patterns similar to altitudinal migrants elsewhere in the world. Because altitudinal migration systems are relatively tractable, they present excellent opportunities for testing hypotheses regarding migration generally. Altitudinal migration has likely been overlooked in North America due to contingency in the history of ornithological research. Our need to understand the patterns and causes of altitudinal migrations has never been greater due to emerging environmental threats to montane systems.
We describe a new collaborative network, the Motus Wildlife Tracking System (Motus; https://motus.org), which is an international network of researchers using coordinated automated radio-telemetry arrays to study movements of small flying organisms including birds, bats, and insects, at local, regional, and hemispheric scales. Radio-telemetry has been a cornerstone of tracking studies for over 50 years, and because of current limitations of geographic positioning systems (GPS) and satellite transmitters, has remained the primary means to track movements of small animals with high temporal and spatial precision. Automated receivers, along with recent miniaturization and digital coding of tags, have further improved the utility of radio-telemetry by allowing many individuals to be tracked continuously and simultaneously across broad landscapes. Motus is novel among automated arrays in that collaborators employ a single radio frequency across receiving stations over a broad geographic scale, allowing individuals to be detected at sites maintained by others. Motus also coordinates, disseminates, and archives detections and associated metadata in a central repository. Combined with the ability to track many individuals simultaneously, Motus has expanded the scope and spatial scale of research questions that can be addressed using radio-telemetry from local to regional and even hemispheric scales. Since its inception in 2012, more than 9000 individuals of over 87 species of birds, bats, and insects have been tracked, resulting in more than 250 million detections. This rich and comprehensive dataset includes detections of individuals during all phases of the annual cycle (breeding, migration, and nonbreeding), and at a variety of spatial scales, resulting in novel insights into the movement behavior of small flying animals. The value of the Motus network will grow as spatial coverage of stations and number of partners and collaborators increases. With continued expansion and support, Motus can provide a framework for global collaboration, and a coordinated approach to solving some of the most complex problems in movement biology and ecology.
Conservation of migratory animals requires information about seasonal survival rates. Identifying factors that limit populations, and the portions of the annual cycle in which they occur, are critical for recognizing and reducing potential threats. However, such data are lacking for virtually all migratory taxa. We investigated patterns and environmental correlates of annual, oversummer, overwinter, and migratory survival for adult male Kirtland’s warblers (Setophaga kirtlandii), an endangered, long-distance migratory songbird. We used Cormack–Jolly–Seber models to analyze two mark–recapture datasets: 2006–2011 on Michigan breeding grounds, and 2003–2010 on Bahamian wintering grounds. The mean annual survival probability was 0.58 ± 0.12 SE. Monthly survival probabilities during the summer and winter stationary periods were relatively high (0.963 ± 0.005 SE and 0.977 ± 0.002 SE, respectively). Monthly survival probability during migratory periods was substantially lower (0.879 ± 0.05 SE), accounting for ~44% of all annual mortality. March rainfall in the Bahamas was the best-supported predictor of annual survival probability and was positively correlated with apparent annual survival in the subsequent year, suggesting that the effects of winter precipitation carried over to influence survival probability of individuals in later seasons. Projection modeling revealed that a decrease in Bahamas March rainfall >12.4% from its current mean could result in negative population growth in this species. Collectively, our results suggest that increased drought during the non-breeding season, which is predicted to occur under multiple climate change scenarios, could have important consequences on the annual survival and population growth rate of Kirtland’s warbler and other Neotropical–Nearctic migratory bird species.
We examined stopover site fidelity exhibited by Tennessee Warblers (Oreothlypis peregrina) and Cape May Warblers (Setophaga tigrina) to a high-elevation banding site in the southern Appalachian Mountains. From 1999 - 2014, 6,175 Tennessee Warblers and 198 Cape May Warblers were captured and banded at Whigg Meadow banding station (Monroe County, Tennessee), with 16 Tennessee Warblers and one Cape May Warbler recaptured in subsequent years. The inter-annual recapture, or the recapture of birds banded in prior years, of 16 Tennessee Warblers documents the highest known incidence of fidelity to a single stopover site in a Nearctic-Neotropical migrant passerine species. These results indicate that fidelity to stopover sites by long-distance migrant passerine species occurs, but may be limited to a specific suite of species. We encourage continued reporting of inter-annual site faithful passerines and research regarding stopover site fidelity and the ecology of stopover sites in order to aid in the conservation efforts of long-distance migrant passerines.
For vertebrates, annual cycles are organized into a series of breeding and non-breeding periods that vary in duration and location but are inextricably linked biologically. Here, we show that our understanding of the fundamental ecology of four vertebrate classes has been limited by a severe breeding season research bias and that studies of individual and population-level responses to natural and anthropogenic change would benefit from a full annual cycle perspective. Recent emergence of new analytical and technological tools for studying individual and population-level animal movement could help reverse this bias. To improve understanding of species biology and reverse the population declines of many vertebrate species, a concerted effort to move beyond single season research is vital.
© 2015 The Author(s).
Full-annual-cycle (FAC) models integrate seasonal demographic and environmental processes to elucidate the factors that limit and regulate animal populations. Unlike traditional, breeding-season-focused models of migratory populations, FAC population models include the effects on population dynamics of events in both the breeding and the nonbreeding season (i.e. winter and migration). Given that migratory birds can spend most of the year away from the breeding grounds and face seasonally specific threats and limitation, FAC models can provide critical and unique insights about their population dynamics. We review existing FAC population model types, including demographic network models, seasonal matrix models, and individual-based models, with examples of each type. We also suggest some approaches new to FAC population modeling—integrated population models and integral projection models— and make recommendations for the development and implementation of these models. Incorporating model components such as density dependence, migratory connectivity (the demographic linkages between breeding and nonbreeding areas), and seasonal interactions can be critical for model realism but can also increase model complexity and development time. Much of the development of FAC population models has been more theoretical than applied. The main limitation to the application of the developed models is availability of empirical data for all annual stages, particularly knowledge of migratory connectivity and density-dependent seasonal survival. As these data become more available, the models outlined here should find additional uses.
Dispersal decisions of songbirds are relatively well understood between breeding seasons, but far less is known about dispersal between nesting attempts and during the molting period. There are several non-mutually exclusive hypotheses for why birds disperse during breeding and molt including: (1) avoiding predation, (2) because of depleted resources, or (3) seeking higher quality habitat. In this study, we evaluated the above hypotheses by radio-tracking a Neotropical migrant, the Wood Thrush (Hylocichla mustelina), during breeding and molt. During breeding, 30% (7/23) of females moved territories within-season. Females were not more likely to move off-territory following nest predation, and dispersing females were not in poorer nutritional state than non-dispersing females prior to the move. However, females occupying nest sites with large trees, high canopy height and percent canopy cover, and low percent ground cover were more likely to move off-territory for their second nest to sites with few large trees, a low canopy height and cover, and high percent ground cover. During the molting period, 61% (28/46) of birds moved off-territory to molt. Molting areas were associated with more shrubs and fruiting trees compared with breeding territories. There were no sex or age effects as to whether a bird molted on or off their breeding territory. We suggest that off-territory movements during the nesting period are to seek more suitable nesting vegetation, rather than specifically avoiding predation or because of reduced resource availability. This study has additionally shown that, without radio-telemetry, detecting off-territory movements during breeding is difficult and neglecting to include these movements may result in an underestimation of annual productivity.
Bird migration is a spectacular natural phenomenon that has generated wonder and interest for centuries. Feats of migration in-spire amazement—individual birds that weigh less than 200 g may log more than 80,000 km annually (Egevang et al. 2010), travel more than 600 km day –1 (Stutchbury et al. 2009, Åkesson et al. 2012), and cross huge geographic barriers such as oceans (Bairlein et al. 2012) and inhospitable deserts (Tøttrup et al. 2012b). Despite the vast geography covered during migration, many birds return to the same territories year after year. Although incredible progress has been made in our understanding of bird migration (Newton 2008), many gaps remain in our knowledge of the migration of small birds. The development of miniaturized tracking technology has produced a wave of research into the migratory behavior of small birds (Fig. 1). The inaugural application of miniaturized geoloca-tors (or "geologgers") on small songbirds in 2007 (Stutchbury et al. 2009) initiated a rapid increase in the number of studies of small landbird migration; there are currently more than 100 permits in North America alone for attaching geolocators to small birds. This technology has been so enthusiastically applied because it provides information critical to conservation and management of declining songbird populations (Faaborg et al. 2010a), as well as the opportunity to test long-standing hypotheses related to en-dogenous control mechanisms, navigation, and energetics (Rob-inson et al. 2010). Although more accurate devices may someday be available for tracking small birds, geolocators are currently the only option for migrants that weigh <50 g (Bridge et al. 2011). The main goal of many geolocator studies to date has been the description of little-known migratory routes and wintering sites (e.g., Beason et al. 2012, Stach et al. 2012). As this technique becomes more widely applied (both geographically within spe-cies and taxonomically across a broad spectrum of small land-birds), researchers can begin to test hypotheses about migration, non-breeding ecology, and behavior to inform conservation mea-sures. Many migratory species are declining; thus, a comprehen-sive understanding of the annual cycle is timely and important for management of species at risk. The purpose of our review is to summarize, for the first time, patterns emerging from geolo-cator studies. We review new data on (1) migratory connectivity, (2) migratory routes and stopovers, (3) intratropical migration of wintering birds, and (4) migration schedules. We then explore questions that can be answered with emerging geolocator studies, and provide a "flight plan" for future work as direct-tracking tech-nology becomes increasingly smaller and more broadly applied.
Garden Warblers Sylvia borin were studied during autumn stopover in Crete before crossing the barrier of the Mediterranean Sea and the Sahara Desert. Birds followed with transmitters show extensive stopover periods, which were longer in first-year birds, 16 days, compared with adult birds, 14 days. The distribution of body masses from birds trapped in fig trees were used to estimate the departure body mass and the results found indicate that both age categories on average depart with a fuel load close to 100% of lean body mass. The movement of transmitter birds shows differences between first-year and adult birds. Adult birds move further away from the release site and many also left the study area. Several were found settled outside the study area, up to 17 km away, indicating that they regularly make longer stopover movements. It is suggested that this might be a result of that they return to a place where they stayed during an earlier migration. It was shown that stopover site fidelity exists and nine garden warblers were recaptured in the area during a following autumn. The results found highlights the importance of stopover areas close to the Sahara Desert.
We examined stopover site fidelity
by Tennessee Warblers (Oreothlypis peregrina) at two
Tennessee banding stations (Whigg Meadow and Big
Bald) operated during fall migration, ,1,000 km from
the nearest breeding areas. We captured and banded
4,324 Tennessee Warblers at Whigg Meadow from
1999 to 2008 with 14 individuals (0.3%) recaptured in
subsequent years. We banded 5,514 Tennessee Warblers
at Big Bald from 2003 to 2008 where, despite
relatively close geographical proximity to Whigg
Meadow (,150 km between sites), no individuals were
recaptured outside of the initial capture year. These
inter-annual recaptures, to our knowledge, reflect the
highest reoccurrence of a Nearctic-neotropical migratory
passerine at a single stopover site. Our results provide
evidence that passerine stopover site fidelity may occur
at considerable distances from both breeding and
wintering areas, and differ between geographically
similar stopover sites.
Nearctic-neotropic migrant birds need to replenish energy reserves during stopover periods to successfully complete their semiannual movements. In this study we used linear models to examine the habitat use of 11 migrant species in northeastern Costa Rica to better understand the influence of food and structural resources on the presence of birds during stopover periods. Our models indicated that frugivorous migrants primarily used food abundance, while insectivorous migrants chiefly used vegetation structure as cues for habitat use during stopover. In addition to habitat use models, we documented fruiting plant phenology and found a general relationship between migrant arrival and the timing of ripe fruit availability. Our results suggest that insectivorous migrants probably rely on structural features when using habitat because it may be inherently difficult to assess cryptic-arthropod availability during a short period of time in a novel habitat, such as stopover periods.
The Klamath Bird Observatory and U.S. Forest Service's Redwood Sciences Laboratory have developed the Klamath Demographic Monitoring Network, a comprehensive bird-monitoring network in southern Oregon and northern California. The Network integrates bird conservation objectives into the ecosystem management process by incorporating academic, scientific, management, and conservation interests to inform the management and conservation process with science. We present examples of how our approach to studying bird populations in the Klamath-Siskiyou Region provides information about bird distribution and demographics. We demonstrate how the Network provides a tool for generating management-related hypotheses and resulting studies.
Between 1984 and 2002,a total of 7643 Bluethroats were ringed and 1054 of these were recaptured
at the International Birding and Research Center (IBRCE) in Eilat,Israel (291330N,
341570E). The autumn migration of Bluethroat begins in September and ends in early
December (median 01-Nov). The spring migration starts in early March and continues till
May (median 21-Mar). Wintering Bluethroats arrive during October and November and stay
in Eilat until March and April. The Bluethroats remain at the winter quarters for up to 4
months,though some individuals could linger for as long as more than 5 months. The majority
of the wintering population was males (65.3%) and adult birds (66.1%),the sex ratio during
winter (65:35) did not differ significantly from the sex ratio during autumn migration (60:40).
The ratio between young and adult birds at Eilat during winter (66:34) differed significantly
from the autumn migration (75:25). Wintering site fidelity for six seasons (consecutive autumn
through spring) from 1996 to 2001 was 1.8%. Wintering site fidelity of Bluethroats
when compared between birds that winter for the second and third season shows a recovery
rate of 37.1%.
Los patrones intraespecíficos del momento en que tiene lugar la migración de otoño no son bien conocidos, particularmente en el oeste de los Estados Unidos. En este estudio (1) describimos el momento en que sucede la migración de otoño y los cocientes de edades de migrantes terrestres en el suroeste de Idaho, (2) examinamos las diferencias en el momento en que sucede la migración entre sexos y clases de edad y (3), demostramos cómo las estrategias de muda prebásica afectan las diferencias en el momento de migración entre clases de edad. Como un grupo, los migrantes neotropicales fueron más comunes desde finales de julio hasta comienzos de septiembre, mientras que los migrantes de la zona templada fueron más comunes entre mediados de septiembre y principios de octubre. La proporción de aves nacidas durante el año fue del 74.5% para todos los migrantes combinados y varió entre especies entre el 33.3% y el 100%. Sólo se detectaron diferencias entre sexos en el momento de migración en pocas especies, y no existieron patrones generales. En 22 de los 31 migrantes neotropicales y de la zona templada que se examinaron existieron diferencias significativas en el momento de migración entre los adultos y las aves en su primer año de vida. En las especies en que los adultos inician la migración otoñal antes de reemplazar sus plumas de vuelo, los adultos migraron antes que las aves jóvenes. Por el contrario, en las especies en que los adultos mudan sus plumas de vuelo en sus sitios de cría o cerca de éstos antes de iniciar la migración, las aves en su primer año de vida migraron antes que los adultos en todos menos un caso. Por lo tanto, parece que la estrategia de muda es un determinante importante de las diferencias intraespecíficas en el momento en que tiene lugar la migración, y de acuerdo a lo que conocemos, nuestro estudio es el primero que documenta este patrón en paserinos migrantes de América del Norte.
An ambitious, comprehensive assessment of the current status of neotropical migratory birds in the USA, and the methods and strategies for conserving migrant populations. This book covers the full scope of the subject, with chapters reviewing and assessing the topics written as consensus documents by several of the leading workers. Contents include population trends, seasonal variations, habitat requirements during migration, impacts and effects of silviculture and agricultural practices, landscape ecology, habitat grazing effects, and single-species versus multiple-species approaches.
This website provides results of temporal and spatial analyses of capture-mark-recapture and constant-effort capture-rate data on 158 landbird species collected as part of the Monitoring Avian Productivity and Survivorship (MAPS) program between 1992 and 2006. The objectives of these analyses are to provide estimates of, and explore relationships among, the vital rates and demographic parameters of each of these species in order to provide hypotheses regarding the demographic drivers of temporal and spatial variation in their population dynamics, especially as these results may help inform research, management, and conservation efforts for them.
Precise locations for the complete feather molt of North American landbirds, relative to their breeding territories, remain undocumented for most species. We analyzed >760,000 records of 140 species at 936 bird-capture stations to assess probabilities of recording both molting landbirds at their breeding sites and breeding birds at molting sites, and to investigate latitudinal, longitudinal, and elevational shifts from breeding to molting grounds. We demonstrate widespread evidence for molt-migrations among a variety of North American landbirds, including many migratory species previously thought to molt on "breeding grounds." Geospatial differences between breeding and molting grounds were detected in all 4 compass directions as well as both upslope and downslope in elevation, while individuals of some species appeared to disperse to specific molting locations not discriminated by spatial direction or elevation from breeding territories. Although western North American species and populations are reported to undergo more molt-migration than eastern species, our molt-movement probabilities were similar in western and eastern North America and were greater in the east than in the west for several species. Combining our results with those of these previous studies, we suggest that many landbird species in western North America move longer distances to molt, whereas many landbirds in eastern North America may equally or more likely move shorter distances between breeding and molting habitats, while remaining within the overall breeding ranges of the species. Heterogeneous molt-movement responses are suggested for many species, which may relate to breeding success, resource availability on breeding territories, weather events, and other factors. Researchers using stable-isotopic, genetic, and geolocator techniques need to consider potential molt-movement strategies, and to incorporate molting habitat requirements into full-annual-cycle conservation efforts.
We report movements and habitat use during the postbreeding period of radio-tagged adult Wood Thrushes (Hylocichla mustelina) at the United States Marine Corps Base, Quantico, Virginia, from May to October 1993 to 1995. Thirty of 61 radio-tagged adults stayed on the study area up to two months after they finished reproductive activities. During this time they underwent molt. Of these 30 birds, 11 (6 females and 5 males) molted in the same sites where they nested, 4 males moved to stands of deciduous saplings adjacent to their nesting territories, and 15 (4 females and 11 males) moved to molting sites 545 to 7,291 m from their nesting territories. We found no clear patterns that sex or reproductive success were related to the probability of moving away from nesting sites to molt, nor that the location of molting adults was correlated with the presence of fruiting plants. However, structural attributes of the vegetation that may enhance predation avoidance, such as the number of woody stems, the density of the understory, and the number of deciduous saplings, were significantly higher in molting sites than in nesting sites. We hypothesize that during molt, Wood Thrushes may need access to 'safe havens' where protection from predators is enhanced. Our study strongly suggests that a conservation strategy that focuses on identifying and protecting nesting habitat is inadequate if the events and needs during the postbreeding period are not considered as well.
This book presents an up-to-date, detailed and thorough review of the most fascinating ecological findings of bird migration. It deals with all aspects of this absorbing subject, including the problems of navigation and vagrancy, the timing and physiological control of migration, the factors that limit their populations, and more. Author, Ian Newton, reveals the extraordinary adaptability of birds to the variable and changing conditions across the globe, including current climate change. This adventurous book places emphasis on ecological aspects, which have received only scant attention in previous publications. Overall, the book provides the most thorough and in-depth appraisal of current information available, with abundant tables, maps and diagrams, and many new insights. Written in a clear and readable style, this book appeals not only to migration researchers in the field and Ornithologists, but to anyone with an interest in this fascinating subject. * Hot ecological aspects include: various types of bird movements, including dispersal and nomadism, and how they relate to food supplies and other external conditions * Contains numerous tables, maps and diagrams, a glossary, and a bibliography of more than 2,700 references * Written by an active researcher with a distinguished career in avian ecology, including migration research.
Documentation of the schedule and pattern of molt and their relation to reproduction and migration departure are important, but often neglected, areas of knowledge. We radio-tagged Wood Thrushes (Hylocichla mustelina), and monitored their movements and behavior on the U.S. Marine Corps Base, Quantico, Virginia (38 degrees 30' N, 77 degrees 30' W) from May-Oct. of 1993-1995. The molt period in adults extended from late July to early October. Molt of flight feathers lasted an average of 38 days (n = 17 birds) and there was no significant difference in duration between sexes. In 21 observed and captured individuals, all the rectrices were lost simultaneously or nearly so, and some individuals dropped several primaries over a few days. Extensive molt in Wood Thrushes apparently impaired flight efficiency, and birds at this stage were remarkably cautious and difficult to capture and observe. All breeding individuals were observed molting 1-4 days after fledgling independence or last-clutch predation, except for one pair that began molt while still caring for fledglings. Our data indicate that energetics or flight efficiency constraints may dictate a separation of molt and migration. We did not observe Wood Thrushes leaving the Marine Base before completion of flight-feather molt. Departure of individuals with molt in body and head, however, was common. We caution against interpreting the lack of observations or captures of molting individuals on breeding sites as evidence that birds actually have left the area. We argue also that current reports on overlapping of molt and migration based on observations of molting individuals out of the breeding range could be misleading because some individuals may leave the breeding area to molt in other places before starting a true migration.
Using a comparative approach, the examination of the effects of fragmentation on three forest-nesting migrants, including oven-bird, red-eyed vireo, and wood thrush was made. Birds were surveyed and reproductive success on 28 study plots in fragmented and contiguous forests in two midwestern regions was monitored. Overall, distribution of individuals between fragmented and contiguous forests appeared to vary among species and regions, but total nest failure was significantly higher in fragments than contiguous forests in both regions for all species.
Adults of several species of western North American passerines are known to migrate to the Mexican monsoon region to undergo molt from July to October before continuing migration to their wintering grounds in the neotropics, but little is known about the biology and habitat requirements of these birds on their molting grounds. Therefore we established 13 banding stations during the monsoon seasons of 2007 and 2008 in southeastern Arizona, central Sonora, and central Sinaloa. We studied the spatial and temporal occurrence of 10 previously known and 9 new species of molt migrants on the molting grounds. In many of these species most or all individuals appeared to undertake molt migration but in others it appeared to be limited to a small proportion of the population, underscoring that molt migration must be defined at the level of the individual rather than of the population. Our results suggest that during the drier 2007 monsoon season molt migrants sought out riparian habitats, whereas in the wetter 2008 season, when the flush of vegetation was greater, they were more widely distributed in drier habitats. Site fidelity to molting grounds was virtually zero, significantly less than site fidelity to banding stations on breeding and winter grounds. Our results suggest that molt migration to the Mexican monsoon region is a stochastic or plastic process, substantially influenced by individual choices related to variation in weather and the preceding breeding season. Our study also emphasizes the need to conserve a mosaic of habitats in the monsoon region appropriate for molting birds.
We documented one Seiurus noveboracensis (Northern Waterthrush) exhibiting stopover-site fidelity by returning to a near-coastal stopover site at the Butler Island Auxiliary Station (BIAS) on the Altamaha Waterfowl Management Area in southeast Georgia during banding operations from 1995–2000. The Northern Waterthrush was recaptured in fall 2000 after being banded at BIAS in fall 1997. Although few individual passerine migrants have exhibited stopover-site fidelity, the majority were recaptured at banding stations nearer (<500 km) breeding populations of the respective species. Stopover-site fidelity is rarely documented in the southeast, as migration banding stations are generally located at coastal migrant traps, which primarily capture hatching-year birds that likely migrate to inland locations in subsequent fall migrations and do not return to coastal migrant traps. High percentages of hatching-year migrants at our near-coastal site suggest that this area is used by migrants in a similar fashion to coastal sites; however, we found possible benefits received by young birds returning to this site in subsequent years. Although rarely documented, passerine migrants may encounter some of the same benefits that wading birds, waterfowl, and shorebirds encounter in using the same stopover locations annually.
I studied 787 female and 510 male Prothonotary Warblers (Protonotaria citrea) breeding in southern Illinois, USA, from 1994 to 2000 to test two competing hy-potheses that may explain between-year breeding-site fidelity in migratory birds. I exper-imentally manipulated the nesting success of randomly chosen female (n 187) and male (n 139) warblers during 1997–2000 to test the ''decision rules'' hypothesis. The site fidelity of individuals increased significantly with an increase in the number of broods produced (zero, one, or two) and 80% of those that were double-brooded returned to sites the following year. Territory fidelity of individuals that returned to study sites also increased with increased reproductive success. The ''renesting stress'' hypothesis was not supported because site fidelity was unaffected by the number of nesting attempts made. Site fidelity did not differ between sexes, but territory fidelity was higher for males than for females. Mate fidelity, age, and brood parasitism by cowbirds had little effect on site and territory fidelity. Nesting success on Prothonotary Warbler territories was predictable between years, and individuals benefited by returning to territories where two broods were produced or by dispersing from territories where no broods were produced. These results support the decision rules hypothesis and demonstrate a causal relationship whereby individuals use their own reproductive experience at a site to assess the current and potential future quality of the location and then respond accordingly by returning or not returning. Decision rules may allow these birds to avoid sites with chronically high rates of nest predation and to concentrate in areas where nesting success is high.
Demographic data from both breeding and non‐breeding periods are needed to manage populations of migratory birds, many of which are declining in abundance and are of conservation concern. Although habitat associations, and to a lesser extent, reproductive biology, are known for many migratory species, few studies have measured survival rates of these birds at different parts of their annual cycle.
Cormack–Jolly–Seber models and Akaike’s information criterion model selection were used to investigate seasonal variation in survival of a Nearctic – Neotropical migrant songbird, the black‐throated blue warbler, Dendroica caerulescens . Seasonal and annual survival were estimated from resightings of colour‐ringed individuals on breeding grounds in New Hampshire, USA from 1986 to 2000 and on winter quarters in Jamaica, West Indies from 1986 to 1999. Warblers were studied each year during the May–August breeding period in New Hampshire and during the October–March overwinter period in Jamaica.
In New Hampshire, males had higher annual survival (0·51 ± 0·03) and recapture probabilities (0·93 ± 0·03) than did females (survival: 0·40 ± 0·04; recapture: 0·87 ± 0·06). In Jamaica, annual survival (0·43 ± 0·03) and recapture (0·95 ± 0·04) probabilities did not differ between sexes. Annual survival and recapture probabilities of young birds (i.e. yearlings in New Hampshire and hatch‐year birds in Jamaica) did not differ from adults, indicating that from the time hatch‐year individuals acquire territories on winter quarters in mid‐October, they survive as well as adults within the same habitat.
Monthly survival probabilities during the summer (May–August) and winter (October–March) stationary periods were high: 1·0 for males in New Hampshire, and 0·99 ± 0·01 for males in Jamaica and for females in both locations.
These annual and seasonal survival estimates were used to calculate warbler survival for the migratory periods. Monthly survival probability during migration ranged from 0·77 to 0·81 ± 0·02. Thus, apparent mortality rates were at least 15 times higher during migration compared to that in the stationary periods, and more than 85% of apparent annual mortality of D. caerulescens occurred during migration.
Additional data from multiple species, especially measures of habitat‐specific demography and dispersal, will improve our understanding of the relative impacts of the breeding, migratory, and winter periods on population dynamics of migratory birds and thus enhance future conservation efforts.
Foragers use a variety of anti-predator behaviours to increase their safety from predators. While foraging, animals should alter usage within or between sites to balance the benefits of feeding with the costs of predation. I tested how the distribution of food abundance and predation danger interacts to explain spatial usage (i.e. distance from shore) by migratory western sandpipers (Calidris mauri) at Boundary Bay, British Columbia, Canada, during northward and southward migrations. At Boundary Bay there are opposing spatial gradients in the distribution of food abundance and safety from predators. Predation danger for sandpipers is high near the shoreline where there is approach cover for falcons and decreases with distance from shore. Food abundance for sandpipers declines as distance from the shoreline increases. Food and danger attributes at Boundary Bay also differ temporally, such that food abundance is higher during southward migration, and predation danger is higher during northward migration. The spatial usage by western sandpipers balances the tradeoff between the opposing spatial gradients in food and safety. For both migratory periods spatial usage of the mudflat by sandpipers is highest at distances from the shoreline where food abundance and predation danger are intermediate. During the northward migration sandpiper usage is highest between 150 and 500 m from the shoreline, and during the southward migration sandpiper usage is highest between 100 and 600 m from the shoreline. Despite temporal differences in food and danger attributes, spatial usage of the site by sandpipers does not differ between migratory periods. Understanding how the distribution of food abundance and predation danger interact to affect the within site usage by shorebirds has important implications for assessments of site quality.
Long-distance migrant passerines are well known to often display high levels of philopatry to breeding and wintering grounds. One could expect that similar selective pressures and similar navigation skills would result in their being faithful to stopover sites, a pattern that has been described for several populations of migratory waders and waterfowl. In this paper, we develop the argument that passerines should suffer from higher costs and receive lower benefits from stopover site faithfulness than waterfowl and waders. Based on Alerstam's (1979)“optimal drift strategy” theory and other considerations, we predict that passerines should have lower stopover site fidelity than geese and waders, and that site faithfulness should decrease with increasing distance from either end of the migratory journey. We present results from a long-term study on the stopover ecology of migrant passerines in southern Portugal that support these predictions and show that, for species and populations that neither nest nor winter in this country, few individuals are faithful to the stopover site. On the other hand, populations that included individuals at (or near to) the start or the end of the migratory journey, had much higher return rates. We could not find any evidence that species linked to scarce habitats, such as wetlands, were more site faithful. Our results are in agreement with several other reports, but in apparent contrast to previous conclusions resulting from some studies involving Old World warblers. These differences are discussed and it is argued that there is no solid evidence to suggest that site fidelity should be important for passerines at stopovers far away from breeding or wintering grounds, meaning that there is a large within-individual variability in the precise migratory routes and stopover sequence used each year.
The decline of many species of Neotropical migrants has prompted increased research on their ecology on their breeding and wintering grounds. However, studies of their ecology during migration are relatively few. Despite documentation of molt-migration in at least six Neotropical passerine species, this phenomenon has been ignored in current conservation strategies for Neotropical migrants. In this review paper, we suggest that molt studies need to be done as a way to refine and improve conservation plans for Neotropical migrants. We identify three important questions that merit further study: (1) which Neotropical migrant species undergo flight feather molt at migratory-stopover sites; (2) where are molt-migration stopover sites geographically located; and (3) why are these sites preferred as stopover sites during molt? Finding answers to these questions will allow us to protect molt staging areas occupied by Neotropical migrants during migration as many wetland and nearshore oceanic habitats have been protected for molting waterfowl, shorebirds, and seabirds.
Many species of birds and mammals are faithful to their natal and breeding site or group. In most of them one sex is more philopatric than the other. In birds it is usually females which disperse more than males; in mammals it is usually males which disperse more than females. Reproductive enhancement through increased access to mates or resources and the avoidance of inbreeding are important in promoting sex differences in dispersal. It is argued that the direction of the sex bias is a consequence of the type of mating system. Philopatry will favour the evolution of cooperative traits between members of the sedentary sex. Disruptive acts will be a feature of dispersers.
The ecological and conservation implications of site fidelity among nearctic-neotropical migrant songbirds wintering in a Costa Rican mangrove forest were examined. During two boreal winters, 168 (24%) of 700 individuals were captured more than once within winter seasons. Among these, birds from six of 15 migratory species were re-trapped. The vast majority of recaptures were either prothonotary warblers Protonotaria citrea or northern waterthrush Seiurus noveboracensis. Between winters, only prothonotary warblers, northern waterthrush and yellow warblers Dendroica petechia were recaptured, with 55 (16%) of 336 individuals originally caught in winter 1990–1991 being re-trapped in winter 1991–1992. Examination of body condition indices revealed no significant difference between prothonotary warblers which returned the second year and those which did not, but northern waterthrush which returned for a second winter had significantly greater body mass and body condition indices than those which did not return. Although we detected no differences in between-year recapture rate for migrants at this site, differences in site fidelity may exist and be an important conservation issue for nearctic-neotropical migrants. Those species with high levels of site fidelity between years may be less adaptable to habitat degradation and loss. As distance between patches of suitable habitat grows with increasing deforestation of tropical zones, even returning to the same region may not lead to the discovery of suitable habitat. Migratory species such as these may be the most vulnerable to population declines in the face of losses on their wintering grounds.
Our understanding of migratory birds' year-round ecology and evolution remains patchy despite recent fundamental advances. Periodic reviews focus future research and inform conservation and management; here, we take advantage of our combined experiences working on Western Hemisphere avian migration systems to highlight recent lessons and critical gaps in knowledge. Among topics discussed are: (1) The pipeline from pure to applied researchers leaves room for improvement. (2) Population limitation and regulation includes both seasonal and between-season interactions. (3) The study of movements of small-bodied species remains a major research frontier. (4) We must increase our understanding of population connectivity. (5) With few exceptions, population regulation has barely been investigated. (6) We have increasingly integrated landscape configuration of habitats, large-scale habitat disturbances, and habitat quality impacts into models of seasonal and overall demographic success. (7) The post-breeding season (late summer for latitudinal migrants) is increasingly appreciated for its impacts on demography. (8) We recognize the diverse ways that avian brood parasites, nest predators, and food availability affect demography. (9) Source-sink and meta-population models help us understand migratory avian distributions among fragmented habitats. (10) Advances in modeling have improved estimates of annual survival and fecundity, but for few species. (11) Populations can be limited by ecological conditions in winter, but habitat needs are poorly known for most species at this time. (12) Migration tends to occupy broad spatial fronts that may change seasonally or when migrants cross major barriers. (13) En route conditions can limit migrant populations; linking migration habitat quality indicators to fitness or population consequences presents a major challenge. (14) A variety of intra-tropical Neotropical migration patterns are recognizable,. but almost nothing is known about these systems beyond descriptions of a few typical species' movements. (15) Global climate change scenarios predict range and phenology shifts of Neotropical migrant bird populations that must be considered in conservation plans. Future studies will depend on new technologies and the integration of modeling with sophisticated, large-spatial-scale measurement and parameter estimation; whether the pace of research and management involving migratory birds can match the growth of environmental threats remains to be seen.