Human encroachment into the natural environment through agricultural expansion has intensified human-wildlife interactions. Negative population impacts are regularly associated with this encroachment; however, some species, including geese, benefit from novel resources these modified environments provide, often resulting in conflict with local stakeholders. Shooting management to reduce populations and/or alter distribution by manipulating the fear landscape is a common approach to mitigate conflicts. However, the efficacy of these strategies in driving redistributions is often unclear. Greenland barnacle geese (Branta leucopsis) wintering on Islay, Scotland have been subject to shooting management to mitigate their effect on farm pastures. We evaluated the effectiveness of this strategy in influencing field use and abundance at an island-wide scale. Using a unique long-term data set (2005-2019) of goose distribution and shooting activity, we assessed within-winter drivers of foraging distribution within improved grassland in relation to habitat variability and shooting disturbance. We found field use was predominantly associated with forage acquisition at a field-scale and low-intensity shooting disturbance had no observed effect on abundance. Foraging was likely prioritised and has a stronger influence than disturbance, though geese did preferentially forage on perceived 'safer' fields (close to roosts, further from roads). Consequently, the impacts on redistribution were more marginal. Synthesis and Applications. Our results demonstrate that to be effective in stimulating redistribution, an understanding of the drivers of site use is crucial for shooting-based disturbance regimes. We emphasise the importance of providing refuges to encourage site use and highlight the importance of considering the spatio-temporal coordination of shooting disturbance to stimulate distributional shifts.

Black-legged kittiwake (Rissa tridactyla) populations are in decline globally, including in Britain and Ireland, which support internationally important numbers. Although kittiwakes typically nest on coastal cliffs, they are known to colonise anthropogenic structures, including offshore oil and gas platforms. Lack of monitoring of offshore platform colonies represents a potentially important gap in our understanding of kittiwake population size and dynamics. The presence of nesting kittiwakes on oil and gas platforms presents a practical challenge for operators in relation to decommissioning and re-purposing works. We use preliminary data from surveys of colonies on offshore oil and gas platforms to speculate on the scale of platform colonisation by kittiwakes and the potentially significant contribution this may make to the wider population. Practical Implication: We identify several research priorities to help address important evidence gaps and inform management strategies: (1) regular monitoring of offshore populations to inform national population censuses, (2) improved understanding of the ecological drivers of offshore breeding including selection of nesting sites and foraging habitats, fitness benefits and connectivity with onshore colonies and (3) collaboration with platform operators to develop practical approaches to minimise impacts of essential operational work on nesting kittiwakes.

Information from throughout the annual cycle is necessary to understand the ecological consequences of global change on migratory marine vertebrates. Northern gannets Morus bassanus are partially migratory seabirds that feed on pelagic fish and fishery discards during breeding periods, but their non-breeding foraging ecology is less well known. Here, we used light-level geolocation tracking of gannets breeding in the UK (Grassholm, Wales) to identify key over-winter locations, combined with stable isotope analysis of winter-grown primary feather keratin and potential fish prey from wintering sites to estimate non-breeding diets using stable isotope mixing models. We tracked gannets to their wintering areas in coastal waters of the Canary Current (n = 15; 75%), Iberian Current (n = 2; 10%) and southwest England/northwest France (n = 3; 15%). Mixing models from the Canary Current and Iberian Coast suggest non-breeding gannets ate mostly pelagic fish, although this varied among individuals (22.3 to 78.2% small pelagics; 17.4 to 70.6% large pelagics), while demersal and/or benthopelagic fish composed 4.4 to 18.4% of the diet. Additionally, we used automatic identification system-derived fishing effort to estimate spatial co-occurrence of wintering gannets with fishing activity. Gannet areas of active use co-occurred with trawler (all types) and fixed gear (anchored longlines, gillnets, pots, and traps) fleets. Direct association between fishing vessels and gannets could not be derived from our tracking data, but the coincident spatial use and dietary preference for heavily targeted fish may indicate a risk of bycatch and potential competition with fisheries. We advocate for increased year-round research, oversight, and monitoring of gannet-vessel interactions and bycatch rates in areas of co-occurrence to understand and mitigate risks and aid in conservation decision making.

Human-modified landscapes have created opportunities for numerous taxa. Agricultural expansion has proven advantageous for several Arctic-breeding goose species, leading to increased abundance and intensified conflict with farmers. Shooting is frequently implemented as a mitigation strategy to control population and via scaring to alter the spatial distribution of conflict species. However, the efficacy of such regimes in manipulating the fear landscape is not always investigated. We developed resource selection functions using GPS-tracking data for Greenland barnacle geese (Branta leucopsis) wintering on Islay, Scotland to assess foraging site choice. We assessed overall foraging site preference and evaluated the influence of shooting management on foraging site selection of key habitats. Barnacle geese selected for improved grassland areas and the likelihood of utilisation varied between these fields according to field-specific management. Protected areas were strongly selected for along with newly reseeded grassland. Field-level exposure to shooting disturbance did not cause a notable change in site selection. Synthesis and Applications: Our results demonstrate the importance of providing refuges within managed agricultural landscapes to encourage site use and minimise conflict. We highlight how low-intensity shooting disturbance may be ineffective in altering winter habitat selection of high-value foraging sites (especially near roosts). If future management aimed to stimulate redistribution, higher intensity shooting disturbance along with the spatial and temporal coordination of shooting effort would likely be required to create a stronger perceived gradient of disturbance risk. Our results demonstrate the importance of providing refuges within managed agricultural landscapes to encourage site use and minimise conflict. We highlight how low-intensity shooting disturbance may be ineffective in altering winter habitat selection of high-value foraging sites (especially near roosts). If future management aimed to stimulate redistribution, higher intensity shooting disturbance along with the spatial and temporal coordination of shooting effort would likely be required to create a stronger perceived gradient of disturbance risk.image

Density-dependent competition for food influences the foraging behaviour and demography of colonial animals, but how this influence varies across a species’ latitudinal range is poorly understood. Here we used satellite tracking from 21 Northern Gannet Morus bassanus colonies (39% of colonies worldwide, supporting 73% of the global population) during chick-rearing to test how foraging trip characteristics (distance and duration) covary with colony size (138–60 953 breeding pairs) and latitude across 89% of their latitudinal range (46.81–71.23° N). Tracking data for 1118 individuals showed that foraging trip duration and maximum distance both increased with square-root colony size. Foraging effort also varied between years for the same colony, consistent with a link to environmental variability. Trip duration and maximum distance also decreased with latitude, after controlling for colony size. Our results are consistent with density-dependent reduction in prey availability influencing colony size and reveal reduced competition at the poleward range margin. This provides a mechanism for rapid population growth at northern colonies and, therefore, a poleward shift in response to environmental change. Further work is required to understand when and how colonial animals deplete nearby prey, along with the positive and negative effects of social foraging behaviour.

Ignoring the dynamic nature of microbial communities risks underestimating the power of microbes to impact the health of their hosts. Microbiomes are thought to be important for host fitness, yet the coarse temporal scale and population-level focus of many studies precludes the ability to investigate the importance of among-individual variation in stability and identify the ecological contexts in which this variation matters. Here we briefly summarise current knowledge of temporal dynamics in wild host-associated microbial communities. We then discuss the implications of among-individual variation in microbiota stability and suggest analytical approaches for understanding these patterns. One major requirement is for future studies to conduct individual-level longitudinal analyses, with some systems already well set up for answering these questions.

The study of animal diets and the proportional contribution that different foods make to their diets is an important task in ecology. Stable Isotope Mixing Models (SIMMs) are an important tool for studying an animal's diet and understanding how the animal interacts with its environment. We present cosimmr, a new R package designed to include covariates when estimating diet proportions in SIMMs, with simple functions to produce plots and summary statistics. The inclusion of covariates allows for users to perform a more in-depth analysis of their system and to gain new insights into the diets of the organisms being studied. A common problem with the previous generation of SIMMs is that they are very slow to produce a posterior distribution of dietary estimates, especially for more complex model structures, such as when covariates are included. The widely-used Markov chain Monte Carlo (MCMC) algorithm used by many traditional SIMMs often requires a very large number of iterations to reach convergence. In contrast, cosimmr uses Fixed Form Variational Bayes (FFVB), which we demonstrate gives up to an order of magnitude speed improvement with no discernible loss of accuracy. We provide a full mathematical description of the model, which includes corrections for trophic discrimination and concentration dependence, and evaluate its performance against the state of the art MixSIAR model. Whilst MCMC is guaranteed to converge to the posterior distribution in the long term, FFVB converges to an approximation of the posterior distribution, which may lead to sub-optimal performance. However we show that the package produces equivalent results in a fraction of the time for all the examples on which we test. The package is designed to be user-friendly and is based on the existing simmr framework.

The use of lead shotgun ammunition for shooting wildfowl has been restricted in England since 1999, but surveys finding lead shot in harvested birds show compliance with regulations has been low. Following the announcement in 2020 of a voluntary transition from lead to non-lead shot by UK shooting organizations, we investigated spatiotemporal variation in the composition of ammunition used for shooting mallards Anas platyrhynchos. We collected 176 harvested mallards during the 2021/22 shooting season and analyzed recent shot extracted from carcasses to determine shot composition. Using a separate collection of ducks of known provenance, we used stable isotope analysis as a means of differentiating captive-reared from wild mallards. This allowed us to understand how compliance might vary between driven game shooters, characterized by shooting birds that are flushed over a stationary line of shooters, and who primarily harvest captive-reared and released ducks, and wild duck shooters. Of 133 mallards containing recent shot, 92 (69%) had been illegally shot with lead. Analysis of this and five comparable surveys between 2001 and 2019 indicates regional and temporal variation in lead shot presence in England. In the North West and West Midlands, the likelihood of mallards containing lead shot decreased significantly over time, but no other regions showed significant changes. The use of non-lead shot types varied over time, with increases in steel shot use approximately matched by declines in bismuth shot. Mallards likely to be reared were more likely to have been shot with lead (75%) than those likely to be wild (48%). This suggests the use of lead shot is more frequent among driven game shooters than wild duck shooters. In England in 2021/22, most mallards continued to be shot with lead, suggesting that neither legislation nor voluntary approaches have been effective in substantially reducing illegal use of lead shot.

Human-wildlife conflict is a global conservation issue, necessitating effective mitigation strategies. Hunting is a common management approach to reduce conflict, but the indirect consequences are often overlooked. Chronic hunting-related disturbance can reduce fitness and redistribute species. In recent decades, goose-agricultural conflict has intensified due to increasing abundance and shifts towards agricultural foraging. On Islay, Scotland, escalating conflict culminated in shooting Greenland barnacle geese Branta leucopsis to reduce damage to agricultural grassland. In this study, we contrast the impact of shooting disturbance on the movement, behavior, energy expenditure and habitat selection of the target species (Greenland barnacle goose) and a vulnerable nontarget species (Greenland white-fronted goose, Anser albifrons flavirostris) using biologging devices (target species: n = 33; nontarget species: n = 94). Both species were displaced by shooting, and greater distances were subsequently traveled by the target species (1.71 km when directly targeted). When disturbed at any distance, total daily movement increased significantly by 1.18 km for the target species but not for the nontarget species. The target species exhibited no accompanying change in diurnal energy expenditure (measured via accelerometery) but foraged in improved grasslands further from roads after shooting disturbance, where disturbance from all sources was likely lower. The significant increases in movement and changes in foraging site selection of the target species could reduce fitness but given the infrequency of shooting disturbances (0.09 per day) there is likely capacity for compensatory feeding to recoup energetic losses. The nontarget species expectedly showed no significant change in energy expenditure, behavior or habitat selection following shooting disturbance, suggesting mitigation strategies have been effective at minimizing fitness impacts. Refuge areas with a 3.5 km diameter (three times the maximum distance from shooting that displacement was detectable) could provide undisturbed foraging for the target species, minimizing compensatory feeding and further agricultural damage. Wildlife managers should, where possible, consider the fitness implications of shooting disturbance, and whether compensatory feeding and redistribution could hamper conflict mitigation. Management strategies should also include species-specific monitoring and mitigation as we have demonstrated differing responses potentially due to imposed mitigation but also differing species ecology and "landscapes of fear."

Conditions experienced by an individual during migration have the potential to shape migratory tactic and in turn fitness. For large birds, environmental conditions encountered during migration have been linked with survival and subsequent reproductive output, but this is less known for smaller birds, hindering our understanding of mechanisms driving population change. By combining breeding and tracking data from 62 pied flycatchers (Ficedula hypoleuca) representing two breeding populations collected over 2016-2020, we determine how variation in migration phenology and tactic among individuals affects subsequent breeding. Departure date from West African non-breeding areas to European breeding grounds was highly variable among individuals and had a strong influence on migration tactic. Early departing individuals had longer spring migrations which included longer staging duration yet arrived at breeding sites and initiated breeding earlier than later departing individuals. Individuals with longer duration spring migrations and early arrival at breeding sites had larger clutches, and for males higher fledging success. We suggest that for pied flycatchers, individual carry-over effects may act through departure phenology from West Africa, and the associated spring migration duration, to influence reproduction. While our results confirm that departure date from non-breeding areas can be associated with breeding success in migratory passerines, we identify spring staging duration as a key component of this process.

Top carnivores can influence the structure of ecological communities, primarily through competition and predation; however, communities are also influenced by bottom-up forces such as anthropogenic habitat disturbance. Top carnivore declines will likely alter competitive dynamics within and amongst sympatric carnivore species. Increasing intraspecific competition is generally predicted to drive niche expansion and/or individual specialisation, while interspecific competition tends to constrain niches. Using stable isotope analysis of whiskers, we studied the effects of Tasmanian devil Sarcophilus harrisii declines upon the population- and individual-level isotopic niches of Tasmanian devils and sympatric spotted-tailed quolls Dasyurus maculatus subsp. maculatus. We investigated whether time since the onset of devil decline (a proxy for severity of decline) and landscape characteristics affected the isotopic niche breadth and overlap of devil and quoll populations. We quantified individual isotopic niche breadth for a subset of Tasmanian devils and spotted-tailed quolls and assessed whether between-site population niche variation was driven by individual-level specialisation. Tasmanian devils and spotted-tailed quolls demonstrated smaller population-level isotopic niche breadths with increasing human-modified habitat, while time since the onset of devil decline had no effect on population-level niche breadth or interspecific niche overlap. Individual isotopic niche breadths of Tasmanian devils and spotted-tailed quolls were narrower in human-modified landscapes, likely driving population isotopic niche contraction, however, the degree of individuals' specialisation relative to one another remained constant. Our results suggest that across varied landscapes, mammalian carnivore niches can be more sensitive to the bottom-up forces of anthropogenic habitat disturbance than to the top-down effects of top carnivore decline.

We introduce an R package for fitting Stable Isotope Mixing Models (SIMMs) via both Markov chain Monte Carlo and Variational Bayes. The package is mainly used for estimating dietary contributions from food sources taken via measurements of stable isotope ratios from animals. It can also be used to estimate proportional contributions of a mixture from known sources, for example apportionment of river sediment, amongst many other use cases. The package contains a simple structure which allows non-expert users to interface with the package, with most of the computational complexity hidden behind the main fitting functions. In this paper we detail the background to these functions and provide case studies on how the package should be used. Further examples are available in the online package vignettes.

RationaleBy combining precision satellite‐tracking with blood sampling, seabirds can be used to validate marine carbon and nitrogen isoscapes, but it is unclear whether a comparable approach using low‐precision light‐level geolocators (GLS) and feather sampling can be similarly effective.MethodsHere we used GLS to identify wintering areas of northern gannets (Morus bassanus) and sampled winter grown feathers (confirmed from image analysis of non‐breeding birds) to test for spatial gradients in δ13C and δ15N in the NE Atlantic.ResultsBy matching winter‐grown feathers with the non‐breeding location of tracked birds we found latitudinal gradients in δ13C and δ15N in neritic waters. Moreover, isotopic patterns were best explained by sea surface temperature. Similar isotope gradients were found in fish muscle sampled at local ports.ConclusionsOur study reveals the potential of using seabird GLS and feathers to reconstruct large‐scale isotopic patterns.

Recent studies have suggested that protected areas often fail to conserve target species. However, the efficacy of terrestrial protected areas is difficult to measure, especially for highly vagile species like migratory birds that may move between protected and unprotected areas throughout their lives. Here, we use a 30-y dataset of detailed demographic data from a migratory waterbird, the Whooper swan (Cygnus cygnus), to assess the value of nature reserves (NRs). We assess how demographic rates vary at sites with varying levels of protection and how they are influenced by movements between sites. Swans had a lower breeding probability when wintering inside NRs than outside but better survival for all age classes, generating a 30-fold higher annual growth rate within NRs. There was also a net movement of individuals from NRs to non-NRs. By combining these demographic rates and estimates of movement (into and out of NRs) into population projection models, we show that the NRs should help to double the population of swans wintering in the United Kingdom by 2030. These results highlight the major effect that spatial management can have on species conservation, even when the areas protected are relatively small and only used during short periods of the life cycle.

Effective marine ecosystem monitoring is critical for sustainable management. Monitoring seabird diets can convey important information on ecosystem health and seabird–fishery interactions. The diet of breeding black-browed albatross ( Thalassarche melanophris ) has previously been assessed using stomach content analysis (SCA) or stable isotope analysis (SIA), but not both methods together. Combining dietary sampling approaches reduces biases associated with using single methods. This study combines SCA and SIA to study the diet of black-browed albatross chicks, with a specific focus on fishery discard consumption, at two Falkland Islands colonies (New Island 51°43′S, 61°18′W and Steeple Jason Island 51°01′S, 61°13′W) during two consecutive breeding seasons (2019 and 2020). SCA provided high taxonomic resolution of short-term diet and priors for stable isotope mixing models, with multiple measures of dietary items (e.g. numeric frequency N%, frequency of occurrence FO%). By contrast, SIA of down feathers provided a single and more integrated dietary signal from throughout chick development. Although the two methods disagreed on the dominant prey group (SCA—crustacean; SIA—pelagic fish), the complementary information suggested a chick diet dominated by natural prey (SCA: 74%–93% [FO], 44%–98% [N]; SIA: minimum 87%–95% contribution). Nonetheless, SCA revealed that a high proportion of breeding adults do take discards. We detected consistent colony-specific diets in relation to prey species, but not in relation to higher discard use. Overall, discard consumption was highest in 2020, the year characterised by the poorest foraging conditions. Our results have implications for fisheries management and future dietary studies assessing discard use.

Abstract Abstract Animal migrations represent the regular movements of trillions of individuals. The scale of these movements has inspired human intrigue for millennia and has been intensively studied by biologists. This research has highlighted the diversity of migratory strategies seen across and within migratory taxa: while some migrants temporarily express phenotypes dedicated to travel, others show little or no phenotypic flexibility in association with migration. However, a vocabulary for describing these contrasting solutions to the performance trade‐offs inherent to the highly dynamic lifestyle of migrants (and strategies intermediate between these two extremes) is currently missing. We propose a taxon‐independent organising framework based on energetics, distinguishing between migrants that forage as they travel (income migrants) and those that fuel migration using energy acquired before departure (capital migrants). Not only does our capital:income continuum of migratory energetics account for the variable extent of phenotypic flexibility within and across migrant populations, but it also aligns with theoreticians' treatment of migration and clarifies how migration impacts other phases of the life cycle. As such, it provides a unifying scale and common vacabulary for comparing the migratory strategies of divergent taxa.

Gut-associated microbial communities are known to play a vital role in the health and fitness of their hosts. Though studies investigating the factors associated with among-individual variation in microbiome structure in wild animal species are increasing, knowledge of this variation at the individual level is scarce, despite the clear link between microbiome and nutritional status uncovered in humans and model organisms. Here, we combine detailed observational data on life history and foraging preference with 16S rRNA profiling of the faecal microbiome to investigate the relationship between diet, microbiome stability and rates of body mass gain in a migratory capital-breeding bird, the light-bellied Brent goose (Branta bernicla hrota). Our findings suggest that generalist feeders have microbiomes that are intermediate in diversity and composition between two foraging specialisms, and also show higher within-individual plasticity. We also suggest a link between foraging phenotype and the rates of mass gain during the spring staging of a capital breeder. This study offers rare insight into individual-level temporal dynamics of the gut microbiome of a wild host. Further work is needed to uncover the functional link between individual dietary choices, gut microbiome structure and stability, and the implications this has for the reproductive success of this capital breeder.

Vagrancy, where individuals occur outside of known population distributions, is a poorly understood ecological phenomenon. It can however be a key driver of site colonisation and range expansion. Evidence is emerging that presumed vagrant Siberian passerines in Western Europe, e.g. Richard’s Pipits Anthus ricardii, are colonists, with geolocator-tracked individuals returning to breed in Siberia after wintering in Western Europe. As such, ‘vagrancy’ patterns in these taxa could provide a model system to understand large-scale range shifts. For example, determining the origins of vagrant individuals and linking these to morphology and arrival date could help to identify the potential drivers of range dynamics. Here, we investigate the origins of vagrant Yellow-browed Warblers Phylloscopus inornatus (a migratory Siberian breeding passerine) in Western Europe by analysing stable hydrogen isotopes, morphology and phenology. We measure the isotopic patterns of feathers grown on the breeding grounds and their relation to those from two sub-species of Common Chiffchaff Phylloscopus collybita. We found that Yellow-browed Warblers have similar hydrogen isotopic signatures (δ2H) to the Siberian sub-species of Common Chiffchaff Phylloscopus collybita tristis and δ2H values did not overlap with those from the European nominate race of Common Chiffchaff Phylloscopus collybita collybita. There was weak evidence that variation in δ2H values was linked to differences in migratory distances in sampled Yellow-browed Warblers. The variation in δ2H values for Yellow-browed Warblers was similar to Chiffchaffs of the collybita and tristis sub-species. This suggests that Yellow-browed Warblers in Western Europe may originate from a relatively broad-front and not exclusively from an expanding western breeding range margin. It is unclear if vagrant Yellow-browed Warblers in Western Europe make viable return migrations to Siberia. If they are, the subset of individuals that become colonists could help us understand how vagrancy drives biogeographic processes, such as the establishment of novel migration routes.

Aims: Understanding the suite of environmental changes impacting migration and disentangling these from the dependencies between migratory stages is fundamental to understanding the drivers and mechanisms causing spatial shifts to migratory bird distributions. In this review, our objectives are to: (i) provide evidence of spatial change at all migratory stages, (ii) identify the key mechanisms driving change, (iii) discuss how anthropogenic change influences migratory patterns, (iv) highlight interdependencies between migratory stages and (v) offer a framework for understanding migratory pattern changes.Location: Migratory land birds globally.Methods: We defined a literature search to find examples of spatial changes in avian migrations and their underlying mechanisms. From the top 1000 search results, sorted by relevance, we retained 81 papers published between 1991 and 2020.Results: Spatial shifts in migratory bird distributions occur throughout the annual cycle, but patterns vary across taxa and migratory stages. Since avian migrants occupy multiple sites across the annual cycle, environmental change has particularly complex repercussions for their distributions. Multiple environmental changes can affect distributions at each migratory stage due to fitness asymmetries between migratory strategies and individuals responding flexibly to environmental changes within and across generations. Spatial changes at one stage (e.g. breeding) can also trigger further indirect spatial changes at other stages (e.g. stopovers) due to dependencies between stages.Conclusions: To understand the drivers and mechanisms underpinning spatial changes, comprehensive year-round distributional data are crucial for observing change across multiple migratory stages and disentangling competing drivers. Biologging technology could elucidate the mechanisms causing changes to individual-level strategies and uncover fitness asymmetries between strategies. Ultimately, gaining a clearer understanding of spatial changes will aid in predicting distributional responses to anthropogenic change in migratory birds. This is paramount for mitigating the effects of anthropogenic change and assessing future population viability within this vulnerable and extensive taxonomic group.

Arctic-nesting geese face energetic challenges during spring migration, including ecological barriers and weather conditions (e.g., precipitation and temperature), which in long-lived species can lead to a trade-off to defer reproduction in favor of greater survival. We used GPS location and acceleration data collected from 35 greater white-fronted geese of the North American midcontinent and Greenland populations at spring migration stopovers, and novel applications of Bayesian dynamic linear models to test daily effects of minimum temperature and precipitation on energy expenditure (i.e., overall dynamic body acceleration, ODBA) and proportion of time spent feeding (PTF), then examined the daily and additive importance of ODBA and PTF on probability of breeding deferral using stochastic antecedent models. We expected distinct responses in behavior and probability of breeding deferral between and within populations due to differences in stopover area availability. Time-varying coefficients of weather conditions were variable between ODBA and PTF, and often did not show consistent patterns among birds, indicating plasticity in how individuals respond to conditions. An increase in antecedent ODBA was associated with a slightly increased probability of deferral in midcontinent geese but not Greenland geese. Probability of deferral decreased with increased PTF in both populations. We did not detect any differentially important time periods. These results suggest either that movements and behavior throughout spring migration do not explain breeding deferral or that ecological linkages between bird decisions during spring and subsequent breeding deferral were different between populations and across migration but occurred at different time scales than those we examined.