Radio‐transmitters do not affect seasonal productivity of female Golden‐winged Warblers

Investigating the potential effects of handling and marking techniques on study animals is important for correct interpretation of research results and to effect progress in data‐collection methods. Few investigators have compared the reproductive output of radio‐tagged and non‐radio‐tagged songbirds, and no one to date has examined the possible effect of radio‐tagging adult songbirds on the survival of their fledglings. In 2011 and 2012, we compared several parameters of reproductive output of two groups of female Golden‐winged Warblers (Vermivora chrysoptera) breeding in Minnesota, including 45 females with radio‐transmitters and 73 females we did not capture, handle, or mark. We found no difference between groups in clutch sizes, hatching success, brood sizes, length of incubation and nestling stages, fledging success, number of fledglings, or survival of fledglings to independence. Thus, radio‐tags had no measurable impact on the productivity of female Golden‐winged Warblers. Our results build upon previous studies where investigators have reported no effects of radio‐tagging on the breeding parameters of songbirds by also demonstrating no effect of radio‐tagging through the post‐fledging period and, therefore, the entire breeding season.     

Effect of Geolocators on Migration and Subsequent Breeding Performance of a Long-Distance Passerine Migrant

Geolocators are small light-weight data loggers used to track individual migratory routes, and their use has increased exponentially in birds. However, the effects of geolocators on individual performance are still poorly known. We studied geolocator effects on a long-distance migrating passerine bird, the northern wheatear (Oenanthe oenanthe L.). We asked the general question of whether geolocators affect migratory behaviour and subsequent reproductive performance of small passerines by comparing arrival time, breeding time, breeding success and survival of geolocator versus control birds of known identity and breeding history. During two years geolocator birds (n=37) displayed a lower apparent survival (30%) as compared to controls (45%, n=164). Furthermore, returning geolocator birds (n=12) arrived on average 3.5 days later, started laying eggs 6.3 days later, and had lower nest success (25%) than control birds (78%). Our results suggest that geolocators affect migratory performance with carry-over effects to the timing of breeding and reproductive success in the subsequent breeding season. We discuss the implications of such geolocator effects for the study of migratory strategies of small passerines in general and suggest how to identify and investigate such effects in the future.     

A comparison of life‐history and parental care in temperate and tropical wrens

Comparing closely related species that live in different environments is a powerful way to understand selective pressures that influence life‐history evolution. We examined a suite of life‐history traits and parental care in neotropical buff‐breasted wrens Cantorchilus leucotis and north‐temperate Carolina wrens Thryothorus ludovicianus (Family Troglodytidae), to test hypotheses about life‐history evolution. As expected, buff‐breasted wrens exhibited smaller clutch sizes and higher annual adult survival than Carolina wrens. We found minimal support for the nest predation hypothesis, as nest survival and age‐corrected provisioning rates to whole broods were similar between species, and number of breeding attempts and breeding season length were greater in temperate wrens. Critical predictions of the food limitation hypothesis were not supported; in particular age‐corrected provisioning rates per nestling were higher in the tropical than temperate species. The adult survival and offspring quality hypothesis garnered the most support, as buff‐breasted wrens exhibited greater age‐corrected provisioning rates per nestling, a longer nestling period, longer re‐nesting intervals following nest success, and lower annual fecundity than Carolina wrens. Despite similarly prolonged breeding seasons, reproductive strategies differ between species with buff‐breasted wrens investing considerably in single broods to optimize first‐year survival and Carolina wrens investing in multiple small broods to optimize annual fecundity.     

Context‐dependent effects of radio transmitter attachment on a small passerine

Biotelemetry devices provide unprecedented insights into the spatial behaviour and ecology of many animals. Quantifying the potential effects of attaching such devices to animals is essential, but certain effects may appear only in specific or particularly stressful contexts. Here we analyse the effects of radio transmitter attachment on great tits Parus major tagged over three environmentally dissimilar years, as part of a project studying social‐ and communication networks. When we radio‐tagged birds before breeding, only those tagged in the coldest spring tended to be less likely to breed than control birds. Breeding probability was independent of relative transmitter weight (between 5 and 8% bodyweight). When we radio‐tagged both parents during nestling provisioning (transmitter weight between 6 and 8%), tagged parents were more likely than control parents to desert their brood in two out of three years, while in the other year no tagged parents deserted. Tagged parents provisioning larger broods were most likely to desert, especially during lower average temperatures. Video analyses did not reveal any transmitter effects on provisioning behaviour of parents in the year with no desertion. We conclude that radio tagging before breeding did not lead to negative effects, regardless of transmitter weight, but that decisions about radio‐tagging both parents during nestling provisioning need to be made with exceptional care, taking both environmental context and transmitter weight into account. Reporting results from long‐term radio‐tracking studies comprising several environmentally variable years is crucial to understand and predict potential transmitter effects and maximise the tremendous potential of biotelemetry.     

Early arrival is not associated with more extra‐pair fertilizations in a long‐distance migratory bird

When assessing the benefits of early arrival date of migratory birds, a hidden and often ignored component of males’ fitness is the higher chance of early‐arriving birds to obtain extra‐pair fertilizations. Here we investigated how extra‐pair paternity might affect the relationship between male arrival date and number of fertilizations in a model study system, the European pied flycatcher Ficedula hypoleuca. For this purpose, we sampled and genotyped breeding pairs, unpaired males and offspring (including embryos from unhatched eggs when possible) of a Dutch pied flycatcher population. Detailed information on arrival date of males, egg laying date of their social mates and nest success was also recorded. Early‐arriving males had early‐laying females and males with early‐laying females had a higher probability of siring extra‐pair eggs and obtain more fertilizations. However, male arrival date alone did not correlate with the probability to gain extra‐pair paternity and neither to the amount of fertilized eggs. Both early‐ and late‐arriving males had a higher probability of losing paternity in their own nest compared to birds with an intermediate arrival date. Finally, late‐arriving males were more likely to remain unpaired but, interestingly, a few of these birds obtained paternity via extra‐pair copulations. Because earlier arrival date did not lead to more extra‐pair fertilizations and because such relationship seems to be driven mainly by the female's laying date, we conclude that the contribution of extra‐pair paternity to the overall fitness benefits of early male arrival date is relatively small.     

Arrival date, age and breeding success in white stork Ciconia ciconia

Early arrival to breeding grounds is a life history trait in birds that can result in fitness benefits. We studied the relationship between arrival date and breeding success of individuals in a central Iberian population of white stork Ciconia ciconia , between 1999 and 2005, and the ways in which other potential factors, such as age or sex, affect this relationship. Our results showed that age was the factor most closely related to arrival date and breeding success. Older individuals returned earlier to the breeding grounds, achieved larger clutch sizes and produced more chicks than younger birds. After controlling statistically for age effect, breeding probability (laid eggs or not) and laying date were still significantly explained by arrival date. A higher probability of failure to reproduce (no eggs laid) was found in birds arriving later than in those arriving early. However, clutch size and nestling success (number of nestlings in the nest 40 days after hatching) were not correlated with arrival date. Food availability in the study area throughout the breeding cycle, due to a nearby rubbish dump, could be the factor mitigating differences in clutch size and nestling success related to individual arrival date.     

Relationship between arrival timing and breeding success of intra‐tropical migratory Fork‐tailed Flycatchers (Tyrannus savana)

For migratory birds, early arrival at breeding areas has many benefits, such as acquisition of better territories and mates. This strategy has been found in numerous species breeding at north‐temperate latitudes, but has not been yet reported for intra‐tropical migratory species. We evaluated the relationship between arrival date, initiation of breeding, and breeding success of Fork‐tailed Flycatchers (Tyrannus savana) breeding in southeastern Brazil and overwintering in northern South America. We color‐banded adult flycatchers during three breeding seasons and searched for them during the following breeding seasons. We also monitored nests from construction until either failure or fledging of young. We found that: (1) male Fork‐tailed Flycatchers arrived at the breeding site earlier than females, (2) males that arrived earlier had greater breeding success, and (3) nests where eggs were laid earlier in the breeding season were more likely to be successful than those where eggs were laid later. Male Fork‐tailed Flycatchers appeared to benefit from early arrival at a tropical breeding site, potentially mediated by their ability to acquire a high‐quality territory and mate as early as possible, and by the ability of their mate to begin breeding as early as possible. Breeding success for female Fork‐tailed Flycatchers may be determined primarily by a combination of the arrival date of their mate and how quickly they can begin breeding. Our results suggest that protandry occurs in an intra‐tropical migratory bird and that early arrival of males and early initiation of reproduction by females results in greater reproductive success. A better understanding of the underlying mechanisms that control the timing of migration and reproduction of this and other intra‐tropical migratory species is important for evaluating the challenges they face in light of current and future rapid environmental changes.     

Examining carry‐over effects of winter habitat on breeding phenology and reproductive success in prairie warblers Setophaga discolor

Winter habitat quality can influence breeding phenology and reproductive success of migratory birds. Using stable isotope ratios of carbon (δ¹³C) from bird claws and red blood cells collected in Massachusetts, USA, we assessed if winter habitat occupancy carried over to affect prairie warbler Setophaga discolor breeding arrival dates, body condition upon arrival, pairing success, first‐egg dates and reproductive success. In two of three years (in 2011 and 2012, but not in 2013), after‐second‐year (ASY) males wintering in drier habitat, as indicated by enriched δ¹³C values, arrived later on the breeding grounds. Based on the North Atlantic Oscillation index, there was likely less rainfall in the Caribbean wintering grounds during the winters of 2011 and 2012 compared to the winter of 2013, suggesting increased winter rainfall in 2013 may have diminished the influence of winter habitat occupancy on arrival date. We did not find any effects of winter habitat on breeding season phenomena for second‐year (SY) males or females, but our sample sizes for these age/sex classes were relatively low. Although winter habitat quality influenced arrival dates of ASY males, there was no evidence that it affected reproductive performance, perhaps because of high rates of nest depredation in our system. Our study adds to a growing body of research that shows the influence of carry‐over effects can differ among species and within populations, and also can be modulated by other environmental conditions. This information enriches our understanding of the role of carry‐over effects in population limitation for migratory birds.     

Nest monitoring does not affect nesting success of Whinchats Saxicola rubetra

It is important to assess the effect that research activities may have on animals in the wild, especially when key parameters, such as breeding success, could potentially be influenced by observer activity. For birds, some studies have suggested that nest monitoring can increase the chances of nest failure due to predation, whereas others suggest that human nest visits may actually deter mammalian predators. Nest monitoring visits can also influence breeding success more indirectly by altering parental provisioning behaviour. Here, the influence of monitoring activities on nest success was examined in a ground‐nesting grassland bird, the Whinchat Saxicola rubetra. During the egg phase, a sample of nests were not visited between the initial finding event and the estimated hatching date; instead, the nest status was assessed at a distance. Daily survival rates (DSR) for these nests were compared with that of nests visited every 2 days. During the nestling phase, the effects of observer nest visits on parental provisioning behaviour were determined. Nest visits were found not to affect egg DSR significantly, and parental provisioning was disrupted for a maximum of 20 min (0.52% of the nestling period) following an observer visit. Given the variation in response to nest visits across species, we suggest that consideration should be given to observer impact in all studies where predation risk is high. Here, we illustrate a method for researchers to assess the impact of their nest visits to ensure they are not biasing estimates of breeding success.     

Handicapped females receive more feedings during incubation from their mates: support for the female nutrition hypothesis

The female nutrition hypothesis posits that provisioning intensity of incubating females by their mates may depend on female needs and ensure proper incubation and a corresponding high hatching and breeding success of breeding pairs. Here, we have handicapped female pied flycatchers Ficedula hypoleuca at the beginning of incubation by clipping two primaries on each wing and filmed nests during incubation and later nestling provisioning to estimate male involvement in incubation feeding at the nest and in offspring care. Incubation feeding was more frequent at late nests. Correcting for this seasonal effect, incubation feeding was significantly affected by treatment and twice as high at experimental as at control nests. There was no effect of the experiment on female incubation attendance. The handicap did not result in any effect on hatching and breeding success, nestling growth and male or female provisioning and mass at the end of the nestling period. Males adjust their incubation feeding activity at the nest to female energetic requirements during incubation.     

Establishing the breeding provenance of a temperate-wintering North American passerine, the Golden-crowned Sparrow, using light-level geolocation

The migratory biology and connectivity of passerines remains poorly known, even for those that move primarily within the temperate zone. We used light-level geolocators to describe the migratory geography of a North American temperate migrant passerine. From February to March of 2010, we attached geolocator tags to 33 Golden-crowned Sparrows (Zonotrichia atricapilla) wintering on the central coast of California, USA, and recovered four tags the following winter (October to December 2010). We used a bayesian state-space model to estimate the most likely breeding locations. All four birds spent the breeding season on the coast of the Gulf of Alaska. These locations spanned approximately 1200 kilometers, and none of the individuals bred in the same location. Speed of migration was nearly twice as fast during spring than fall. The return rate of birds tagged the previous season (33%) was similar to that of control birds (39%), but comparing return rates was complicated because 7 of 11 returning birds had lost their tags. For birds that we recaptured before spring migration, we found no significant difference in mass change between tagged and control birds. Our results provide insight into the previously-unknown breeding provenance of a wintering population of Golden-crowned Sparrows and provide more evidence of the contributions that light-level geolocation can make to our understanding of the migratory geography of small passerines.     

Effect of alarm calling by male Red‐winged Blackbirds on nestling begging and female provisioning behavior

ABSTRACT Nestling begging and parental provisioning can attract nest predators and reduce reproductive success, so parents and their offspring might be expected to respond adaptively by minimizing predator‐attracting cues when predators threaten nests. Male Red‐winged Blackbirds (Agelaius phoeniceus) are well known for their antipredator alarm calls that contain information about the approach of potential nest predators. We examined the begging behavior of nestlings and the provisioning behavior of females in response to antipredator alarm calls of males to test the adaptive response hypothesis. Playback experiments provided no evidence that alarm calls function to switch off vocal begging; nestlings were equally likely to beg vocally during playback and control periods. Video recordings showed that male alarm calling had no significant effect on inappropriate vocal begging (in the absence of an adult), but significantly reduced the incidence of spontaneous calling (in the absence of begging). Adult females responded to male antipredator alarm calls by delaying their provisioning visits. In addition, although having no significant effect on use of nest‐arriving calls by females, male alarm calling significantly reduced their use of nest‐leaving calls. We conclude that nestling and female Red‐winged Blackbirds respond to male alarm calls in ways that might reduce the risk of predation, but nestlings beg vocally when females arrive to feed them, regardless of male alarm calling, perhaps to avoid a competitive disadvantage with broodmates.     

The breeding biology of the Dalmatian Pelican Pelecanus crispus

The breeding biology of the Dalmatian Pelican Pelecanus crispus , a vulnerable bird species in the Palaearctic, has been studied for 7 years at Lake Mikri Prespa, a continental wetland and Tsoukalio lagoon, a coastal wetland within the Amvrakikos Gulf. The two colonies showed stability, with fluctuations in the number of breeding attempts each year varying by about 30% over a period of 7 years. The date of arrival at the breeding sites and the date of laying of the first egg varied between mid-February and mid-March. The egglaying period (including renesting) varied between 18 and 114 days between years. The annual average clutch size varied between 1.60 and 1.94 eggs per nest. The incubation period averaged 31.4 ± 1.4 days. The overall hatching success varied from 36% to 70%. Egg losses were mainly due to nest abandonment, infertile eggs and eggs rolled from the nests. The Dalmatian Pelican chicks took 11–12 weeks to fledge. Nestling mortality was very low in contrast to other species of pelican. Such a low nestling mortality explains why the breeding success each year is largely explained by the hatching success.     

Brood provisioning rates and fledgling behavior of Cordilleran Flycatchers in southwestern Colorado

The behavior of young songbirds after fledging is one of the least understood phases of the breeding cycle, although parental provisioning rates and movement of fledglings are key to understanding life history evolution. We studied Cordilleran Flycatchers (Empidonax occidentalis) at two sites in southwestern Colorado, USA, from 2012 to 2017. We banded and sexed breeding adults to determine the relative contributions of males and females to nestling and fledgling care, and attached radio‐transmitters to nestlings to facilitate observations of brood behavior after fledging. Females made 60% and 78% of total observed feedings of nestlings and fledglings, respectively. Parental provisioning rates increased with nestling age, and per‐nestling provisioning rates increased with brood size. Parental provisioning rates declined just before fledging, then increased just after fledging. Fledging times of individuals in broods were asynchronous and concentrated during the late afternoon and early evening. Males stopped caring for fledglings before females even though this species is single‐brooded, with some late‐season broods being abandoned by males. Broods spent the first three weeks after fledging within 400 m of nests, after which they began to disperse. Most aspects of the breeding biology of Cordilleran Flycatchers in our study, including the duration of nestling and fledging periods, female‐dominated provisioning, and movement patterns of fledglings, were similar to those of other Empidonax species. However, the times when young fledged were not concentrated in the morning as reported in most other songbirds, and this result warrants additional study of the timing of fledging in ecologically and taxonomically similar species. The increased per‐nestling provisioning rate with increasing brood size was unexpected, and additional study is needed to determine if this increase results from a trade‐off between adult annual survival and productivity favoring increased provisioning of young in larger broods, or from the existence of high‐quality individuals where larger clutches and higher provisioning rates are linked.     

Decline of a montane Mediterranean pied flycatcher Ficedula hypoleuca population in relation to climate

Certain populations of long‐distance migratory birds are suffering declines, which may be attributed to effects of climate change. In this article, we have analysed a long‐term (1991–2015) data set on a pied flycatcher Ficedula hypoleuca population breeding in nest‐boxes in a Mediterranean montane oak forest, exploring the trends in population size due to changes in nestling recruitment, female survival and female immigration. We have related these changes in population parameters to local climate, winter NAO index and to breeding density. During the last 25 yr the population has declined by half, mainly in association with a decrease in nestling mass and structural size which had repercussions on the probability of nestling recruitment to the population. Lower local nestling recruitment in certain years was linked to lower female immigration rate in the same years. On the other hand, the local survival of females remained stable throughout the study period. Laying date and breeding success were negatively affected by local temperatures while breeding, recruitment rate likewise by minimum temperature prior to breeding in April. As minimum April temperatures have increased across the study period, this may have affected recruitment and immigration rates negatively. On the other hand, tarsus length and body mass of nestlings were positively associated with winter NAO index, pointing to more global climatic links. Moreover, there was also a negative temporal trend in body mass of adults, implying increasingly difficult conditions for breeding. Declining recruit production in the study area could be attributed to a mismatch between the timing of arrival and breeding in the population, and the peak of food availability in this area.     

An experimental evaluation of the effects of geolocator design and attachment method on between‐year survival on whinchats Saxicola rubetra

Data from location logging tags have revolutionised our understanding of migration ecology, but methods of tagging that do not compromise survival need to be identified. We compared resighting rates for 156 geolocator‐tagged and 316 colour ringed‐only whinchats on their African wintering grounds after migration to and from eastern Europe in two separate years. We experimentally varied both light stalk length (0, 5 and 10 mm) and harness material (elastic or non‐elastic nylon braid tied on, leg‐loop ‘Rappole’ harnesses) in the second year using a reasonably balanced design (all tags in the first year used an elastic harness and 10 mm light stalk). Tags weighed 0.63 g (0.01 SE), representing 4.1% of average body mass. There was no overall significant reduction in between‐year resighting rate (our proxy for survival) comparing tagged and untagged birds in either year. When comparing within tagged birds, however, using a tied harness significantly reduced resighting rate by 53% on average compared to using an elastic harness (in all models), but stalk length effects were not statistically significant in any model considered. There was no strong evidence that the fit (relative tightness) or added tag mass affected survival, although tied tags were fitted more tightly later in the study, and birds fitted with tied tags later may have had lower survival. Overall, on a precautionary principle, deploying tags with non‐elastic tied harnesses should be avoided because the necessary fit, so as not to reduce survival, is time‐consuming to achieve and does not necessarily improve with experience. Geolocator tags of the recommended percentage of body mass fitted with elastic leg‐loop harnesses and with short light stalks can be used without survival effects in small long‐distance migrant birds.     

Light‐level geolocators reveal migratory connectivity in European populations of pied flycatchers Ficedula hypoleuca

Understanding what drives or prevents long‐distance migrants to respond to environmental change requires basic knowledge about the wintering and breeding grounds, and the timing of movements between them. Both strong and weak migratory connectivity have been reported for Palearctic passerines wintering in Africa, but this remains unknown for most species. We investigated whether pied flycatchers Ficedula hypoleuca from different breeding populations also differ in wintering locations in west‐Africa. Light‐level geolocator data revealed that flycatchers from different breeding populations travelled to different wintering sites, despite similarity in routes during most of the autumn migration. We found support for strong migratory connectivity showing an unexpected pattern: individuals breeding in Fennoscandia (S‐Finland and S‐Norway) wintered further west compared to individuals breeding at more southern latitudes in the Netherlands and SW‐United Kingdom. The same pattern was found in ring recovery data from sub‐Saharan Africa of individuals with confirmed breeding origin. Furthermore, population‐specific migratory connectivity was associated with geographical variation in breeding and migration phenology: birds from populations which breed and migrate earlier wintered further east than birds from ‘late’ populations. There was no indication that wintering locations were affected by geolocation deployment, as we found high repeatability and consistency in δ¹³C and δ¹⁵N stable isotope ratios of winter grown feathers of individuals with and without a geolocator. We discuss the potential ecological factors causing such an unexpected pattern of migratory connectivity. We hypothesise that population differences in wintering longitudes of pied flycatchers result from geographical variation in breeding phenology and the timing of fuelling for spring migration at the wintering grounds. Future research should aim at describing how temporal dynamics in food availability across the wintering range affects migration, wintering distribution and populations’ capacity to respond to environmental changes.     

The relationship between introduced European Starlings and the reproductive activities of Mountain Bluebirds and Tree Swallows in British Columbia,Canada

The European Starling Sturnus vulgaris is an introduced species in North America and is an aggressive competitor for tree cavity nest‐sites. Starlings are commonly considered to influence nest‐site selection and reproductive success of native cavity‐nesting species negatively. We examined the relationship between Starling nest density and the fecundity of two native secondary cavity‐using passerines, Mountain Bluebird Sialia currucoides and Tree Swallow Tachycineta bicolor. We monitored a total of 622 nests (approximately equal numbers for each of the three species) in woodpecker‐excavated and naturally occurring cavities in 29 small forest groves in central British Columbia, Canada, between 2000 and 2009. The dimensions of cavities used and the timing of nest initiation overlapped for all species, although Starlings initiated clutches earliest. Mixed‐effects models were used to assess whether nest abundance, clutch size or nest success were affected directly by Starling nest abundance, or indirectly via a shift in cavity selection or timing of breeding. Starlings and Mountain Bluebirds showed inverse trends in nest abundance. Mountain Bluebird clutch sizes were smaller if they were initiated later in the breeding season. There was weak evidence that Tree Swallow clutch size decreased with cavity depth when Starling nests were abundant, and increased with cavity depth where there were few Starling nests. We conclude that despite the aggressive nature of this exotic cavity‐nester, the influence of Starlings on native secondary cavity‐nesting passerines is modest where cavities are abundant.     

Cooperative breeding shapes post‐fledging survival in an Afrotropical forest bird

For avian group living to be evolutionary stable, multiple fitness benefits are expected. Yet, the difficulty of tracking fledglings, and thus estimating their survival rates, limits our knowledge on how such benefits may manifest postfledging. We radio‐tagged breeding females of the Afrotropical cooperatively breeding Placid greenbul (Phyllastrephus placidus) during nesting. Tracking these females after fledging permitted us to locate juvenile birds, their parents, and any helpers present and to build individual fledgling resighting datasets without incurring mortality costs or causing premature fledging due to handling or transmitter effects. A Bayesian framework was used to infer age‐specific mortality rates in relation to group size, fledging date, maternal condition, and nestling condition. Postfledging survival was positively related to group size, with fledglings raised in groups with four helpers showing nearly 30% higher survival until independence compared with pair‐only offspring, independent of fledging date, maternal condition or nestling condition. Our results demonstrate the importance of studying the early dependency period just after fledging when assessing presumed benefits of cooperative breeding. While studying small, mobile organisms after they leave the nest remains highly challenging, we argue that the telemetric approach proposed here may be a broadly applicable method to obtain unbiased estimates of postfledging survival.     

Inter‐annual variation in the breeding chronology of arctic shorebirds: effects of weather,snow melt and predators

Arctic breeding shorebirds travel thousands of kilometres between their wintering and breeding grounds, yet the period over which they arrive and begin to initiate nests spans only several weeks. We investigated the role of local conditions such as weather, snow cover and predator abundance on the timing of arrival and breeding for shorebirds at four sites in the eastern Canadian arctic. Over 11 years, we monitored the arrival of 12 species and found 821 nests. Weather was highly variable over the course of this study, and the date of 50% snow cover varied by up to three weeks between years. In contrast, timing of arrival varied by one week or less at our sites, and was not well predicted by local conditions such as temperature, wind or snow melt. Timing of breeding was related to the date of 50% snow melt, with later snow melt resulting in delayed breeding. Higher predator abundance resulted in earlier nesting than would be predicted by snow cover alone. We hypothesise that when predation risk is high, the value of potential re‐nesting exceeds the energetic risks of early breeding. Synchrony of breeding was significantly higher in late breeding years suggesting a relatively fixed date for the termination of nest initiation, after which nesting is no longer profitable.