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Alves J.A.,University of East Anglia | Gunnarsson T.G.,University of Iceland | Potts P.M.,Farlington Ringing Group | Sutherland W.J.,University of Cambridge | Gill J.A.,University of East Anglia
Ecology and Evolution | Year: 2013

In migratory species, sexual size dimorphism can mean differing energetic requirements for males and females. Differences in the costs of migration and in the environmental conditions occurring throughout the range may therefore result in sex-biases in distribution and resource use at different spatial scales. In order to identify the scale at which sexual segregation operates, and thus the scale at which environmental changes may have sex-biased impacts, we use range-wide tracking of individually color-ringed Icelandic black-tailed godwits (Limosa limosa islandica) to quantify sexual segregation at scales ranging from the occupation of sites throughout the non-breeding range to within-site differences in distribution and resource use. Throughout the range of this migratory shorebird, there is no evidence of large-scale sex differences in distribution during the non-breeding season. However, the sexes differ in their selection of prey types and sizes, which results in small-scale sexual segregation within estuaries. The scale of sexual segregation therefore depends on the scale of variation in resource distribution, which, in this system, is primarily within estuaries. Sexual segregation in within-site distribution and resource use means that local-scale anthropogenic impacts on estuarine benthic prey communities may disproportionately affect the sexes in these migratory shorebirds. © 2013 The Authors. Ecology and Evolution.

Pardal S.,University of Coimbra | Alves J.A.,University of East Anglia | Ze-Ze L.,Health Vectors | Osorio H.,Health Vectors | And 11 more authors.
Journal of Ornithology | Year: 2014

Migratory shorebirds are exposed to a wide range of pathogens along their migratory flyways, but their capacity to acquire or spread pathogens beyond endemic areas is poorly known. We focused on the spillover and acquisition of mosquito-borne pathogens such as haemosporidians and West Nile virus (WNV) on key-staging Iberian wetlands during different seasons. We screened seven shorebird species (447 individuals), and detected low haemosporidian prevalence (0.6 %). Furthermore, no WNV infections could be detected, though 6.2 % revealed antibodies against flaviviruses. Although Iberian wetlands congregate numerous shorebirds of different species and origins, the potential introduction of foreign pathogens is not a common event. © 2013 Dt. Ornithologen-Gesellschaft e.V.

Alves J.A.,University of East Anglia | Gunnarsson T.G.,University of Iceland | Hayhow D.B.,University of East Anglia | Appleton G.F.,British Trust for Ornithology | And 3 more authors.
Ecology | Year: 2013

The relative fitness of individuals across a population can shape distributions and drive population growth rates. Migratory species often winter over large geographic ranges, and individuals in different locations experience very different environmental conditions, including different migration costs, which can potentially create fitness inequalities. Here we used energetics models to quantify the trade-offs experienced by a migratory shorebird species at locations throughout the nonbreeding range, and the associated consequences for migratory performance, survival, and breeding habitat quality. Individuals experiencing more favorable winter conditions had higher survival rates, arrived on the breeding grounds earlier, and occupied better quality breeding areas, even when migration costs are substantially higher, than individuals from locations where the energy balance on the wintering grounds was less favorable. The energy costs and benefits of occupying different winter locations can therefore create fitness inequalities which can shape the distribution and population-wide demography of migratory species. © 2013 by the Ecological Society of America.

Gill J.A.,University of East Anglia | Alves J.A.,University of East Anglia | Sutherland W.J.,University of Cambridge | Appleton G.F.,British Trust for Ornithology | And 2 more authors.
Proceedings of the Royal Society B: Biological Sciences | Year: 2014

Recent advances in spring arrival dates have been reported in many migratory species but the mechanism driving these advances is unknown. As population declines are most widely reported in species that are not advancing migration, there is an urgent need to identify the mechanisms facilitating and constraining these advances. Individual plasticity in timing of migration in response to changing climatic conditions is commonly proposed to drive these advances but plasticity in individual migratory timings is rarely observed. For a shorebird population that has significantly advanced migration in recent decades, we show that individual arrival dates are highly consistent between years, but that the arrival dates of newrecruits to the population are significantly earlier now than in previous years. Several mechanisms could drive advances in recruit arrival, none of which require individual plasticity or rapid evolution of migration timings. In particular, advances in nest-laying dates could result in advanced recruit arrival, if benefits of early hatching facilitate early subsequent spring migration. This mechanism could also explain why arrival dates of short-distance migrants, which generally return to breeding sites earlier and have greater scope for advance laying, are advancing more rapidly than long-distance migrants. © 2013 The Authors.

Alves J.A.,University of East Anglia | Gunnarsson T.G.,University of Iceland | Potts P.M.,Farlington Ringing Group | Gelinaud G.,Bretagne Vivante SEPNB | And 2 more authors.
Oikos | Year: 2012

For many migratory bird species, the latitudinal range of the winter distribution spans thousands of kilometres, thus encompassing considerable variation in individual migration distances. Pressure to winter near breeding areas is thought to be a strong driver of the evolution of migration patterns, as individuals undertaking a shorter migration are generally considered to benefit from earlier arrival on the breeding grounds. However, the influence of migration distance on timing of arrival is difficult to quantify because of the large scales over which individuals must be tracked. Using a unique dataset of individually-marked Icelandic black-tailed godwits Limosa limosa islandica tracked throughout the migratory range by a network of hundreds of volunteer observers, we quantify the consequences of migrating different distances for the use of stop-over sites and timing of arrival in Iceland. Modelling of potential flight distances and tracking of individuals from across the winter range shows that individuals wintering further from the breeding grounds must undertake a stop-over during spring migration. However, despite travelling twice the distance and undertaking a stop-over, individuals wintering furthest from the breeding grounds are able to overtake their conspecifics on spring migration and arrive earlier in Iceland. Wintering further from the breeding grounds can therefore be advantageous in migratory species, even when this requires the use of stop-over sites which lengthen the migratory journey. As early arrival on breeding sites confers advantages for breeding success, the capacity of longer distance migrants to overtake conspecifics is likely to influence the fitness consequences of individual migration strategies. Variation in the quality of wintering and stopover sites throughout the range can therefore outweigh the benefits of wintering close to the breeding grounds, and may be a primary driver of the evolution of specific migration routes and patterns. © 2011 The Authors. Oikos © 2012 Nordic Society Oikos.

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