Tree swallow (Tachycineta bicolor) breeding success in Ithaca, NY, USA, over the past quarter century has shown generally healthy fledgling production punctuated by years of high nestling mortality. This study tested the potential effects that temperature may have on the food supply and breeding success of swallows. Data from 17 years of daily insect samples were used to relate flying insect abundances to daily maximum temperatures and to define “cold snaps” as strings of consecutive days when the maximum temperatures did not exceed critical temperatures. The distributions of cold snaps and chick mortality events were investigated both through detailed reconstructions of the fates and fate dates of individual chicks, focused on the three breeding seasons of lowest fledging success, and with less detailed brood-level analyses of a larger 11-year dataset including years of more moderate mortality. Mark–recapture analyses of daily brood survival rate (DSR) reveal very strong support for the effects of cold temperatures on brood survival rates, and all the top models agree on a critical temperature of 18.5 °C for insect flight activity in Ithaca. The individual-level analyses, focused on years of higher mortality, favored a 3-day cold snap definition as the most predictive of DSR effects, whereas the larger-scale brood-level analyses revealed 1- and 2-day cold snaps as having the most significant effects on DSR. Regardless, all analyses reveal that, in an age of generally warmer climates, the largest effect of weather on swallow fledgling production is from cold temperatures.Electronic supplementary materialThe online version of this article (doi:10.1007/s00442-013-2605-z) contains supplementary material, which is available to authorized users.

1. Light-level geolocator tags use ambient light recordings to estimate the whereabouts of an individual over the time it carried the device. Over the past decade, these tags have emerged as an important tool and have been used extensively for tracking animal migrations, most commonly small birds.

Published version [Abstract:]Reductions in body size are increasingly identified as a response to climate warming. Here we present evidence for a case of such body shrinkage, potentially due to malnutrition in early life. We show that an avian long-distance migrant (red knot Calidris c. canutus), experiencing globally unrivaled warming rates at its high-Arctic breeding grounds, produces smaller offspring with shorter bills during summers with early snowmelt. This has consequences half a world away where short-billed individuals have reduced survival on their tropical wintering grounds. This is associated with these molluscivores eating fewer deeply buried bivalve prey and more shallowly buried seagrass rhizomes. We suggest seasonal migrants experience reduced fitness at one end of their range due to a changing climate at the other end. Published version 3Phenological changes and geographical range shifts represent well-known responses to climate change (1). A third broadly observed response to global warming appears to be shrinkage of bodies (2-5). It has been hypothesized that body shrinkage is a genetic micro-evolutionary response to warming due to smaller individuals being better able to dissipate body heat due to a larger body surface/volume ratio (e.g., Bergmann's rule (2)). Conversely, it has been put forward that climate change may disrupt trophic interactions, potentially leading to malnutrition during an organism's juvenile life stage (6, 7). As poor growth may not be compensated for later in life (8), this would lead to smaller bodies (i.e., shrinkage as a phenotypically plastic response).Under climate change, some regions are warming up faster than others. Especially in the Arctic, warming has been observed at unprecedented rates (9, 10). Hence, body-size reductions would be expected to be most pronounced in the world's most northerly region (6). Many Arctic-breeding avian species, however, are long-distance migrants spending the northern winter at lower latitudes (11), where the impacts of climatic change are less obvious.Here, based on the analysis of satellite data, we show that over the past 33 years, snowmelt has occurred progressively earlier on the high-Arctic breeding grounds of the red knot (Calidris canutus canutus) at Taimyr Peninsula ( Fig. 1; 76-78°N), changing at a rate of about half a day per year ( Fig. 2A; R 2 = .32, F1,31 = 14.77, P < .001; see Table S1 and Figs. S1-S3). During these three decades, 1,990 juvenile red knots were caught and their body sizes measured in Gdańsk Bay, Poland, during their first southward migration to the West-African nonbreeding grounds (Fig. 1). These juvenile birds were smaller after Arctic summers with an early snowmelt, notably with respect to body mass ( Fig. 2B; AIC c = 14775.24, P < .0005; Table S2), bill length ( Fig. 2C; AICc = 7610.48, P < .005; Table S3), and overall body size (PC1 on bill, tarsus, and wing; Table S4; AICc = 5925.22, P < .05). The models best explaining variation in bill length and overall body size additionally included breedin...

Please refer to our instructions for authors for full details on manuscript preparation. Please note that this template should act as a guide on content, but doesn't necessarily need to be followed for style and formatting. Our typesetters will set your manuscript into house style after acceptance.*Author for correspondence (Susanne.akesson@biol.lu.se). †Present address: Department of Biology, Lund University, Ecology Building, SE-223 62 Lund, Sweden 2 Summary Migratory birds regularly perform impressive long-distance flights, which are timed relative to the anticipated environmental resources at destination areas that can be several thousand kilometres away. Timely migration requires diverse strategies and adaptations that involve an intricate interplay between internal clock mechanisms and environmental conditions across the annual cycle. Here we review what challenges birds face during long migrations to keep track of time as they exploit geographically distant resources that may vary in availability and predictability, and summarise the clock mechanisms that enable them to succeed. We examine the following challenges: departing in time for spring and autumn migration, in anticipation of future environmental conditions; using clocks on the move, for example for orientation, navigation, and stopover; strategies of adhering to, or adjusting the time program while fitting their activities into an annual cycle; and keeping pace with a world of rapidly changing environments. We then elaborate these themes by case studies representing long-distance migrating birds with different annual movement patterns and associated adaptations of their circannual programs. We discuss the current knowledge on how endogenous migration programs interact with external information across the annual cycle, how components of annual cycle programs encode topography and range expansions, and how fitness may be affected when mismatches between timing and environmental conditions occur. Lastly, we outline open questions and propose future research directions. Non-technical summaryMigratory birds perform impressive long-distance flights, timed relative to the availability of resources in different geographical areas. To manage this birds use different strategies including an interplay between internal clock mechanisms and environmental conditions across the annual cycle. Here we review what challenges birds face during long migrations to keep track of time as they exploit geographically distant resources that may vary in availability and predictability, and summarise the clock mechanisms that enable them to meet these challenges. We discuss how range expansions affect components of annual cycle programs, and how mismatches between timing and environment may affect reproductive success.3

Under climate warming, migratory birds should align reproduction dates with advancing plant and arthropod phenology. To arrive on the breeding grounds earlier, migrants may speed up spring migration by curtailing the time spent en route, possibly at the cost of decreased survival rates. Based on a decades-long series of observations along an entire flyway, we show that when refuelling time is limited, variation in food abundance in the spring staging area affects fitness. Bar-tailed godwits migrating from West Africa to the Siberian Arctic reduce refuelling time at their European staging site and thus maintain a close match between breeding and tundra phenology. Annual survival probability decreases with shorter refuelling times, but correlates positively with refuelling rate, which in turn is correlated with food abundance in the staging area. This chain of effects implies that conditions in the temperate zone determine the ability of godwits to cope with climate-related changes in the Arctic.

BackgroundSolar archival tags (henceforth called geolocators) are tracking devices deployed on animals to reconstruct their long-distance movements on the basis of locations inferred post hoc with reference to the geographical and seasonal variations in the timing and speeds of sunrise and sunset. The increased use of geolocators has created a need for analytical tools to produce accurate and objective estimates of migration routes that are explicit in their uncertainty about the position estimates.ResultsWe developed a hidden Markov chain model for the analysis of geolocator data. This model estimates tracks for animals with complex migratory behaviour by combining: (1) a shading-insensitive, template-fit physical model, (2) an uncorrelated random walk movement model that includes migratory and sedentary behavioural states, and (3) spatially explicit behavioural masks.The model is implemented in a specially developed open source R package FLightR. We used the particle filter (PF) algorithm to provide relatively fast model posterior computation. We illustrate our modelling approach with analysis of simulated data for stationary tags and of real tracks of both a tree swallow Tachycineta bicolor migrating along the east and a golden-crowned sparrow Zonotrichia atricapilla migrating along the west coast of North America.ConclusionsWe provide a model that increases accuracy in analyses of noisy data and movements of animals with complicated migration behaviour. It provides posterior distributions for the positions of animals, their behavioural states (e.g., migrating or sedentary), and distance and direction of movement.Our approach allows biologists to estimate locations of animals with complex migratory behaviour based on raw light data. This model advances the current methods for estimating migration tracks from solar geolocation, and will benefit a fast-growing number of tracking studies with this technology.

Summary1. Solar geolocators are relatively cheap and simple tools which are widely used to study the migration of animals, especially birds. The methods to estimate the geographic positions from the light-intensity patterns collected by these loggers, however, are still under development. 2. The accurate reconstruction of the annual schedules and movement patterns of individual animals requires analytical methods which provide estimates of daily locations, distances between the locations and the directions of movement, with measures of their uncertainty. 3. The new R package FLIGHTR meets all these requirements. It enables refined and statistically validated estimations of movement patterns of birds. Here, we present main features of this advanced package.

hours of those determined by the GPS tracker, whereas GeoLight's estimates were less precise. For the analysed track, FLightR represents an improvement over GeoLight; if true for other species and conditions, FLightR will hopefully help establish more precise and accurate uses of geolocation data in tracking studies. To aid future improvements in the analysis of solar geolocation data, we also provide the GPS and geolocation data files together with our R scripts as supplementary material.3