Assortative mating in two populations of Short‐tailed Albatross Phoebastria albatrus on Torishima

Assortative mating is an important pre‐mating isolation mechanism that has been observed in some wild populations of seabirds. The Short‐tailed Albatross Phoebastria albatrus is a globally Vulnerable seabird that breeds mainly on Torishima and the Senkaku Islands in the north‐western Pacific Ocean. Our previous studies suggested that two genetically distinct populations exist, one on Torishima and the other on the Senkaku Islands. Recently, however, several un‐ringed birds in subadult plumage have been observed breeding on Torishima in the Hatsunezaki colony. As almost all birds hatched on Torishima since 1979 have been ringed, the natal site of the un‐ringed birds was suspected to be the Senkaku Islands. Genetic differences between the two populations would reveal the natal sites of un‐ringed birds. By observing the ring status (ringed or un‐ringed) of mating pairs and analysing the mitochondrial DNA (mtDNA) control region 2 of un‐ringed birds, we assessed whether birds that originated from Torishima and the Senkaku Islands achieved pre‐mating isolation. There was a small number of pairs on Torishima that consisted of one ringed and one un‐ringed bird, but the observed number was significantly lower than that expected if ringed and un‐ringed birds mated randomly. Furthermore, mtDNA analyses of nine un‐ringed birds demonstrated that all belonged to a particular haplotype clade from the Senkaku Islands. These results show that birds from Torishima and the Senkaku Islands mate assortatively but that there is incomplete pre‐mating isolation between birds from the two island groups. The pre‐mating isolation of these two populations of Short‐tailed Albatross could arise from differences in the timing of breeding and incompatibility in mating displays. As the divergence between the two populations is unlikely to be sufficient to achieve complete post‐mating isolation, the two groups are likely to be hybridizing. Further studies using molecular and/or behavioural analyses would be required to reveal the evolutionary significance of hybridization between these two populations.     

Ringing or colour-banding does not increase predation mortality in redshanksTringa totanus

The use of metal and colour‐rings or bands as a means of measuring survival, movements and behaviour in birds is universal and fundamental to testing ecological and evolutionary theories. The practice rests on the largely untested assumption that the rings do not affect survival. However this assumption may not hold for several reasons, for example because the ‘oddity effect’ predicts predators select prey that appear different to their neighbours in order to avoid the ‘confusion effect’. We compared the foraging behaviour and the death rates of redshanks Tringa totanus conspicuously marked with six colour rings and one metal ring each to unmarked birds in a study system, where routinely up to 50% of the total population are killed by avian predators during a winter. If avian predators selectively target and/or have a higher capture success of ringed birds then we would predict the proportion of colour‐ringed birds in the population to decline through a winter. The proportion of colour‐ringed birds in the population did not change over the course of three separate winters, and in one winter the ratio of marked:unmarked birds found killed by sparrowhawks Accipiter nisus was the same as the ratio of marked birds alive in the population. In the year with largest sample size, power was sufficient to detect a greater than 2.2% difference in predation rate between ringed and unringed groups. The average kill rate difference between ringed and unringed birds across the three winters was less than 1% (0.73±2.2%) suggesting that even if there were differences in predation rate that were not detected because of low statistical power they were extremely small. There were no differences in any foraging measures comparing ringed and unringed birds, suggesting that the rings did not affect the ability of birds to meet their daily energy budgets. The results showed that colour‐ringed birds were not preferentially targeted or killed by avian predators, and suggest that the presence of a metal and even several large colour‐rings is unlikely to affect behaviour and predation mortality even under extreme selection.     

Intercolony movement and behaviour of immature Guillemots Uria aalge

A minimum of 61 Guillemots Uria aalge ringed as chicks at other colonies was recorded at the Isle of May between 1987 and 1991 (four prior to 1990, six in 1990, 51 in 1991). Two were adults and 59 were immatures. Most of the British and Irish colonies where many chicks had been ringed were represented. Higher proportions of birds ringed at colonies relatively close to the Isle of May were observed compared to birds ringed at more distant sites. Visitors ranged in age from 2 to 5 years, with single 10- and 14-year-olds. Relatively fewer 2- and 5- than 3- and 4-year-old birds were seen. Visiting birds were usually recorded once only, significantly less often than native immatures of the same age, except for 2-year-olds. The proportion of birds occupying sites on intertidal rocks as against sites in the colony appeared to be higher compared with native birds of the same age. Visiting birds formed a substantial proportion of the immature population. Ten immature birds from the Isle of May were recorded elsewhere. Four of these had been seen on the Isle of May previously, and four were seen there subsequently. A 6-year-old hatched at Sumburgh ( c. 420 km by sea) bred at the Isle of May in 1992.     

Estimating dispersal distributions at multiple scales: within‐colony and among‐colony dispersal rates,distances and directions in European Shags Phalacrocorax aristotelis

Knowledge of the rate, distance and direction of dispersal within and among breeding areas is required to understand and predict demographic and genetic connectivity and resulting population and evolutionary dynamics. However dispersal rates, and the full distributions of dispersal distances and directions, are rarely comprehensively estimated across all spatial scales relevant to wild populations. We used re‐sightings of European Shags Phalacrocorax aristotelis colour‐ringed as chicks on the Isle of May (IoM), UK, to quantify rates, distances and directions of dispersal from natal to subsequent breeding sites both within IoM (within‐colony dispersal) and across 27 other breeding colonies covering 1045 km of coastline (among‐colony dispersal). Additionally, we used non‐breeding season surveys covering 895 km of coastline to estimate breeding season detection probability and hence potential bias in estimated dispersal parameters. Within IoM, 99.6% of individuals dispersed between their natal and observed breeding nest‐site. The distribution of within‐colony dispersal distances was right‐skewed; mean distance was shorter than expected given random settlement within IoM, yet some individuals dispersed long distances within the colony. The distribution of within‐colony dispersal directions was non‐uniform but did not differ from expectation given the spatial arrangement of nest‐sites. However, 10% of all 460 colour‐ringed adults that were located breeding had dispersed to a different colony. The maximum observed dispersal distance (170 km) was much smaller than the maximum distance surveyed (690 km). The distribution of among‐colony dispersal distances was again right‐skewed. Among‐colony dispersal was directional, and differed from random expectation and from the distribution of within‐colony dispersal directions. Non‐breeding season surveys suggested that the probability of detecting a colour‐ringed adult at its breeding location was high in the northeastern UK (98%). Estimated dispersal rates and distributions were therefore robust to incomplete detection. Overall, these data demonstrate skewed and directionally divergent dispersal distributions across small (within‐colony) and large (among‐colony) scales, indicating that dispersal could create genetic and demographic connectivity within the study area.     

Stable isotopes can be used to infer the overwintering locations of prebreeding marine birds in the Canadian Arctic

Although assessments of winter carryover effects on fitness‐related breeding parameters are vital for determining the links between environmental variation and fitness, direct methods of determining overwintering distributions (e.g., electronic tracking) can be expensive, limiting the number of individuals studied. Alternatively, stable isotope analysis in specific tissues can be used as an indirect means of determining individual overwintering areas of residency. Although increasingly used to infer the overwintering distributions of terrestrial birds, stable isotopes have been used less often to infer overwintering areas of marine birds. Using Arctic‐breeding common eiders, we test the effectiveness of an integrated stable isotope approach (13‐carbon, 15‐nitrogen, and 2‐hydrogen) to infer overwintering locations. Knowing the overwinter destinations of eiders from tracking studies at our study colony at East Bay Island, Nunavut, we sampled claw and blood tissues at two known overwintering locations, Nuuk, Greenland, and Newfoundland, Canada. These two locations yielded distinct tissue‐specific isotopic profiles. We then compared the isotope profiles of tissues collected from eiders upon their arrival at our breeding colony, and used a k‐means cluster analysis approach to match arriving eiders to an overwintering group. Samples from the claws of eiders were most effective for determining overwinter origin, due to this tissue's slow growth rate relative to the 40‐day turnover rate of blood. Despite taking an integrative approach using multiple isotopes, k‐means cluster analysis was most effective when using 13‐carbon alone to assign eiders to an overwintering group. Our research demonstrates that it is possible to use stable isotope analysis to assign an overwintering location to a marine bird. There are few examples of the effective use of this technique on a marine bird at this scale; we provide a framework for applying this technique to detect changes in the migration phenology of birds' responses to rapid changes in the Arctic.     

Searching for potential wintering and migration areas of a Danish Barn Swallow population in South Africa by correlating NDVI with survival estimates

On the basis of correlation analyses between annual Normalised Difference Vegetation Index (NDVI) values in Africa and the annual survival rate estimated for a breeding population of barn swallows Hirundo rustica from Denmark, we identified potential wintering and migration areas in South Africa during December–February and March–May, when barn swallows commonly occur in South Africa. During December–February we identified potential wintering areas only in the western part of South Africa, in the Karoo. Potential areas in the central and eastern parts of the country were only identified during March–May. NDVI values in the Karoo during March–May explained most of the variance in annual adult survival rate of the population. The high ratio of European ringed barn swallows among controlled individuals in the Karoo was similar to the ratio that would be expected based on the number of ringed barn swallows and the population sizes of barn swallows in north-western European breeding populations. The level of this ratio in the Karoo was higher than in any other locality in the central and eastern parts of South Africa and Botswana, indicating that ringed birds from the eastern flyway are absent to a much smaller extent than ringed birds from the western flyway. This approach shows that the NDVI and survival method can focus ringing efforts to regions and areas that are likely to harbour specific breeding populations, thereby helping to identify potential wintering and migration areas for breeding populations of migratory birds.     

High juvenile annual survival probabilities in Southern Rockhopper Penguins Eudyptes chrysocome are independent of individual fledging traits

Juvenile survival is an important demographic parameter. Southern Rockhopper Penguins Eudyptes chrysocome have undergone a dramatic population decline in the past century across their distribution, but the demographic processes are poorly understood. To estimate juvenile annual survival probabilities, Rockhopper Penguin chicks from two cohorts on New Island, Falkland Islands, were marked with transponders and recorded in subsequent years using an automated gateway. We first estimated annual survival and detection probabilities using a Cormack‐Jolly‐Seber (CJS) model, and found that both probabilities were extremely high (81% in the first and 98% in the second, third and fourth years of life), even in comparison with adult birds. Because detection probability after 3 years was effectively 1, and our sample size (n = 114) was too small to explore the effects of individual traits on survival in a CJS model, we assessed whether sex, cohort, body mass and laying sequence affected whether juveniles returned to the colony during their first 3 years of life using a simple generalized linear model that assumed perfect detection. Juveniles from the first cohort and males showed a higher return probability than juveniles from the second cohort and females. There was no clear effect of fledging body mass on return rate, probably related to the favourable environmental conditions during the study period. The laying sequence did not markedly affect the return probability of chicks, indicating that, once fledged, first‐laid A‐chicks have the same probability to return as second‐laid B‐chicks despite a much larger initial maternal investment in B‐eggs in this species. This study demonstrates extraordinarily high juvenile survival probabilities and will help to understand the recent changes in the population dynamics of the Falkland Islands Southern Rockhopper Penguins.     

Colony specific variation in the use of a moulting site in the migratory little tern Sterna albifrons

Individual-based data on little terns Sterna albifrons at a post-breeding moulting area were used to investigate the spatial extent at which this site attract birds. Combining information collected on young terns, ringed at the natal colonies, with that on birds captured a few months later at the moulting site, we estimated a survival/movement parameter for each age-by-colony combination. This parameter is the product between the survival probability and the probability to visit the moulting site. The distance between the natal colony and the moulting site negatively influenced the probability of reaching the site in yearlings. Having corrected for the distance from the moulting area, colony characteristics explained only about 10% of the spatial variation in the survival/movement parameter of juveniles. In older birds that had visited the site at least once in their life, neither the colony nor the distance affected the survival/movement parameter significantly. The average annual adult survival/movement probability was 0.90. Juvenile survival between June and September was 0.60. Overall results suggest that the moulting area could act as a 'population funnel' within a system of moult migration that involves birds breeding up to 500 km away. However, other unknown moulting site must exist within this area that could be important for the conservation of the species.     

The post-fledging survival of young Guillemots Uria aalge in relation to hatching date and growth

The post-fledging survival of a total of 1277 young Guillemots Uria aalge ringed in 6 years was assessed using sightings of 267 individuals back at the natal colony and recoveries of 46 ringed birds. In two years there was a significant decline in survival prospects with estimated hatching date, the first time such a trend has been demonstrated in the Alcidae. In these years pairs breeding early had a 2–3 times greater chance of having a young survive to return to the colony than pairs breeding three weeks later. Hatching date had no effect on survival prospects in the other four seasons and in none of the years did chick body condition have a demonstrable effect on post-fledging survival.     

Growth and demography of a re‐introduced population of White‐tailed Eagles Haliaeetus albicilla

White‐tailed Eagles Haliaeetus albicilla became extinct in Britain in 1918 following prolonged persecution. Intensive conservation efforts since the 1970s have included the re‐introduction of the species to Britain through two phases of release of Norwegian fledglings in western Scotland in 1975–85 and 1993–98. Population growth and breeding success have been monitored closely to the present day, aided by the use of patagial tags to individually mark most released birds as well as a high proportion of wild‐bred nestlings. This study reviews the growth and demography of this re‐introduced population, and makes comparisons with other European populations. For the first time, we compare the demographic rates of released and wild‐bred birds in the Scottish population. Breeding success in the Scottish population has increased over time as the average age and experience of individuals in the population have increased, and success tends to be higher where one or both adults are wild‐bred. Current levels of breeding success remain low compared with some other populations in Europe, but similar to those in Norway where weather conditions and food availability are likely to be most similar. Survival rates in Scotland are similar to those recorded elsewhere, but survival rates of released birds are lower than those of wild‐bred birds, especially during the first 3 years of life. Despite the effect of lower survival rates of released birds in limiting overall population growth rate, the recent rate of growth of the Scottish population remains high relative to other recovering populations across Europe. Differences in demographic rates of wild‐bred and released birds suggest that in future re‐introduction programmes, steps to maximize the success and output of the earliest breeding attempts would help ensure the most rapid shift to a population composed largely of wild‐bred birds, which should then have a higher rate of increase.     

Breeding dispersal patterns within a large Sand Martin (Riparia riparia) colony

Colonial birds when returning to breed to a previous location can face different settling options regarding their position in the colony. The decision could be influenced by information gained from the conspecifics’ performance, known as habitat copying. Colonial Sand Martins (Riparia riparia) cannot use evident physical cues when returning to breeding sites, as their nesting substrate is usually renewing completely. We investigated settlement decisions of breeding birds in a unique situation at a large colony along the Tisza River, Hungary, where the nesting substrate was renewed completely in two consecutive years. Breeding birds were ringed at 7-m-long sections of the colony, with totals of 6 sections in 2000 and 20 sections in 2001. Aggregation levels of philopatric birds were estimated by calculating individual distances (expressed in sections) between each recaptured bird. From 1,494 adult birds ringed in the first year, 128 individuals returned to breed in the same colony. The distance to the nearest neighbour in the year 2000 predicted the settlement distance in the next year, indicating a clear preference of breeding closer to the neighbours of the previous year than expected by chance. Age composition had an uneven distribution in the colony, as sections where no clumped resettlement occurred had fewer old individuals than the other sections. Morphological measurements were not clearly different between colony sections. This non-random settlement pattern suggests the existence of breeding groups that could disperse together without being attached to a specific colony site.     

Among‐colony synchrony in the survival of Common Guillemots Uria aalge reflects shared wintering areas

Spatiotemporal variation in survival may be an important driver of multi‐population dynamics in many wild animal species, yet few scientific studies have addressed this issue, primarily due to a lack of sufficiently comprehensive and detailed datasets. Synchrony in survival rates among different, often distant, subpopulations appears to be common, caused by spatially correlated environmental conditions or by movement of animals from different sites such that their ranges overlap. Many seabird populations are effectively isolated during the breeding season because colonies are widely separated, but over the winter, birds disperse widely and there may be much mixing between different populations. The non‐breeding season is also the period of main mortality for seabirds. Using mark–recapture and ring‐recovery data, we tested for spatial, temporal and age‐related correlations in survival of Common Guillemots Uria aalge among three widely separated Scottish colonies that have varying overlap in their overwintering distributions. Survival was highly correlated over time for colonies/age‐classes sharing wintering areas and, except in 2004, was essentially uncorrelated for those with separate wintering areas. These results strongly suggest that one or more aspects of the winter environment are responsible for spatiotemporal variation in survival of British Guillemots, and provide insight into the factors driving large‐scale population dynamics of the species.     

Tracing site‐specific isotopic signatures along a Blue Tit Cyanistes caeruleus food chain

Food chains culminating with temperate insectivorous passerines are well described, yet whether trophic webs can be site‐specific remains a largely unexplored question. In the case of site‐ or habitat‐specificity of food webs, stable isotope signatures of bird feathers may enable assignment of unmarked individuals to a site or a habitat of origin. We address this question in landscapes that include contrasting forest habitat patches with either deciduous Downy Oak Quercus humilis or evergreen Holm Oak Quercus ilex as dominant tree species. First, we examine the spatial variation across habitats and sites in the stable isotope ratios of carbon (δ¹³C) and nitrogen (δ¹⁵N) along the oak leaf–Tortrix moth Tortrix viridana caterpillar–Blue Tit Cyanistes caeruleus food chain. Secondly, we assess whether the isotopic signatures allow for correct assignment of individual birds to their site or habitat of origin. At the scale of the landscape, stable isotope values enabled identification of the different components of the Blue Tit food chain: from oak leaves to Blue Tit nestlings and yearling birds. However, isotopic signatures were site‐specific (i.e. geographical) more than habitat‐specific (i.e. deciduous vs. evergreen oaks). Discriminant analyses correctly assigned 85% of nestlings and 83% of resident yearling birds, indicating a pronounced effect of site on Blue Tit feather isotopic signatures. We thereby demonstrate that isotopes reflect a stronger association of locally born birds to the local features of their habitat than that of un‐ringed yearling birds, whose plumage may have grown while in a wider geographical area. This study provides evidence of site‐specific isotopic signatures from oak leaves to Blue Tit feathers at a fine spatial scale.     

Equal nonbreeding period survival in adults and juveniles of a long‐distant migrant bird

In migrant birds, survival estimates for the different life‐history stages between fledging and first breeding are scarce. First‐year survival is shown to be strongly reduced compared with annual survival of adult birds. However, it remains unclear whether the main bottleneck in juvenile long‐distant migrants occurs in the postfledging period within the breeding ranges or en route. Quantifying survival rates during different life‐history stages and during different periods of the migration cycle is crucial to understand forces driving the evolution of optimal life histories in migrant birds. Here, we estimate survival rates of adult and juvenile barn swallows (Hirundo rustica L.) in the breeding and nonbreeding areas using a population model integrating survival estimates in the breeding ranges based on a large radio‐telemetry data set and published estimates of demographic parameters from large‐scale population‐monitoring projects across Switzerland. Input parameters included the country‐wide population trend, annual productivity estimates of the double‐brooded species, and year‐to‐year survival corrected for breeding dispersal. Juvenile survival in the 3‐week postfledging period was low (S = 0.32; SE = 0.05), whereas in the rest of the annual cycle survival estimates of adults and juveniles were similarly high (S > 0.957). Thus, the postfledging period was the main survival bottleneck, revealing the striking result that nonbreeding period mortality (including migration) is not higher for juveniles than for adult birds. Therefore, focusing future research on sources of variation in postfledging mortality can provide new insights into determinants of population dynamics and life‐history evolution of migrant birds.     

Effects of winter food provisioning on the phenotypes of breeding blue tits

Throughout the Western World, huge numbers of people regularly supply food for wild birds. However, evidence of negative impacts of winter feeding on future reproduction has highlighted a need to improve understanding of the underlying mechanisms shaping avian responses to supplementary food. Here, we test the possibility that carry‐over effects are mediated via their impact on the phenotypes of breeding birds, either by influencing the phenotypic structure of populations through changes in winter survival and/or by more direct effects on the condition of breeding birds. Using a landscape‐scale 3‐year study of blue tits (Cyanistes caeruleus), we demonstrate the importance of nutritional composition of supplementary food in determining carry‐over effect outcomes. We show that breeding populations which had access to vitamin E‐rich foods during the previous winter were comprised of individuals with reduced feather carotenoid concentrations, indicative of lower pre‐feeding phenotypic condition, compared to fat‐fed and unfed populations. This suggests that supplementary feeding in winter can result in altered population phenotypic structure at the time of breeding, perhaps by enhancing survival and recruitment of lower quality individuals. However, supplementation of a fat‐rich diet during winter was detrimental to the oxidative state of breeding birds, with these phenotypic differences ultimately found to impact upon reproductive success. Our findings demonstrate the complex nature by which supplementary feeding can influence wild bird populations.     

An ‘ecological trap’ for yellow warbler nest microhabitat selection

Contrary to assumptions of habitat selection theory, field studies frequently detect ‘ecological traps’, where animals prefer habitats conferring lower fitness than available alternatives. Evidence for traps includes cases where birds prefer breeding habitats associated with relatively high nest predation rates despite the importance of nest survival to avian fitness. Because birds select breeding habitat at multiple spatial scales, the processes underlying traps for birds are likely scale‐dependent. We studied a potential ecological trap for a population of yellow warblers Dendroica petechia while paying specific attention to spatial scale. We quantified nest microhabitat preference by comparing nest‐ versus random‐site microhabitat structure and related preferred microhabitat features with nest survival. Over a nine‐year study period and three study sites, we found a consistently negative relationship between preferred microhabitat patches and nest survival rates. Data from experimental nests described a similar relationship, corroborating the apparent positive relationship between preferred microhabitat and nest predation. As do other songbirds, yellow warblers select breeding habitat in at least two steps at two spatial scales; (1) they select territories at a coarser spatial scale and (2) nest microhabitats at a finer scale from within individual territories. By comparing nest versus random sites within territories, we showed that maladaptive nest microhabitat preferences arose during within‐territory nest site selection (step 2). Furthermore, nest predation rates varied at a fine enough scale to provide individual yellow warblers with lower‐predation alternatives to preferred microhabitats. Given these results, tradeoffs between nest survival and other fitness components are unlikely since fitness components other than nest survival are probably more relevant to territory‐scale habitat selection. Instead, exchanges of individuals among populations facing different predation regimes, the recent proliferation of the parasitic brown‐headed cowbird Molothrus ater, and/or anthropogenic changes to riparian vegetation structure are more likely explanations.     

Mechanisms of colony selection by first‐year Lesser Kestrels Falco naumanni

In colonial species, first‐time breeders may use the number of settled conspecifics in colony selection, but such a relationship is confused by the correlation between colony size and nest‐site availability. To distinguish conspecific attraction from neutral colony selection, we experimentally increased nest availability for first‐year Lesser Kestrels Falco naumanni, allowing us to dissociate the number of vacant nest‐sites from colony size at the arrival time of first‐year birds. Under natural conditions, the number of first‐year birds settling was positively correlated with both the number of philopatric and the total number of breeding pairs (colony size) already settled. However, the probability of occupation of experimentally manipulated nests by first‐year birds was independent of colony size. In experimental colonies, the number of first‐year birds settling was positively correlated with the number of manipulated nest‐sites but not with the number of conspecifics. Overall, these results support a neutral colony selection by first‐year Lesser Kestrels based on nest‐site availability.     

Spatial and temporal variation in population trends in a long‐distance migratory bird

Aim Over the past three decades, evidence has been growing that many Afro‐Palaearctic migratory bird populations have suffered sustained and severe declines. As causes of these declines exist across both the breeding and non‐breeding season, identifying potential drivers of population change is complex. In order to explore the roles of changes in regional and local environmental conditions on population change, we examine spatial and temporal variation in population trajectories of one of Europe’s most abundant Afro‐Palaearctic summer migrants, the willow warbler, Phylloscopus trochilus. Location Britain and Ireland. Methods We use national survey data from Britain and Ireland (BBS: BTO/RSPB/JNCC Breeding Bird Survey and CBS: BWI/NPWS/Heritage Council Countryside Breeding Survey) from 1994 to 2006 to model the spatial and temporal variation in willow warbler population trends. Results Across Britain and Ireland, population trends follow a gradient from sharp declines in the south and east of England to shallow declines and/or slight increases in parts of north and west England, across Scotland and Ireland. Decreasing the spatial scale of analysis reveals variation in both the rate and spatial extent of population change within central England and the majority of Scotland. The rates of population change also vary temporally; declines in the south of England are shallower now than at the start of the time series, whereas populations further north in Britain have undergone periods of increase and decline. Main conclusion These patterns suggest that regional‐scale drivers, such as changing climatic conditions, and local‐scale processes, such as habitat change, are interacting to produce spatially variable population trends. We discuss the potential mechanisms underlying these interactions and the challenges in addressing such changes at scales relevant to migratory species.     

GPS tracking of the foraging movements of Manx Shearwaters Puffinus puffinus breeding on Skomer Island, Wales

We report the first successful use of miniature Global Positioning System loggers to track the ocean‐going behaviour of a c. 400 g seabird, the Manx Shearwater Puffinus puffinus. Breeding birds were tracked over three field seasons during the incubation and chick‐rearing periods on their foraging excursions from the large colony on Skomer Island, Pembrokeshire, UK. Foraging effort was concentrated in the Irish Sea. Likely foraging areas were identified to the north, and more diffusely to the west of the colony. No foraging excursions were recorded significantly to the south of the colony, conflicting with the conclusions of earlier studies based on ringing recoveries and observations. We discuss several explanations including the hypothesis that foraging may have shifted substantially northwards in recent decades. We found no obvious relationship between birds’ positions and water depth, although there was a suggestion that observations at night were in shallower water than those during the day. We also found that, despite the fact that Shearwaters can be observed rafting off‐shore from their colonies in the hours prior to making landfall at night, breeding birds are usually located much further from the colony in the last 8 h before arrival, a finding that has significance for the likely effectiveness of marine protection areas if they are only local to the colony. Short sequences of precise second‐by‐second fixes showed that movement speeds were bimodal, corresponding to sitting on the water (most common at night and around midday) and flying (most common in the morning and evening), with flight behaviour separable into erratic (indicative of searching for food) and directional (indicative of travelling). We also provide a first direct measurement of mean flight speed during directional flight (c. 40 km/h), slower than a Shearwater's predicted maximum range velocity, suggesting that birds are exploiting wave or dynamic soaring during long‐distance travel.     

Local use of landfills by a yellow‐legged gull population suggests distance‐dependent resource exploitation

Understanding the use of feeding sources at the local scale is crucial in comprehending the factors driving population dynamics, dispersal and territory use. Many gull (Larus spp.) populations have increased sharply, which is partly promoted by their use of landfills as a food resource. Although at the large scale it is known that birds from mainland colonies feed more on landfills than those from offshore colonies, at the local scale, this distance‐dependent exploitation has been little studied. Here, then, we study whether the extent of gulls’ use of landfill is distance‐dependent through the study of 3 different gull colonies and five separate landfill sites within a relatively small geographical area. After controlling for bird numbers by both age cohort and colony, we observed that the number of gulls found at each landfill was colony dependent and that it decreased non‐linearly with increased distance to place of birth.