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Lok T.,University of Groningen | Lok T.,Netherlands Institute for Sea Research | Overdijk O.,Werkgroep Lepelaar | Tinbergen J.M.,University of Groningen | And 2 more authors.
Animal Behaviour | Year: 2011

Migrant birds face a choice where to spend the winter. Presumably there is a trade-off between migration distance (costs) and the quality of the wintering site (benefits). Wintering site fidelity is often high and increases with age. Hypotheses to explain such a pattern assume that wintering site choice maximizes fitness. We compared wintering site choice and age-dependent site fidelity in Eurasian spoonbills, Platalea leucorodia leucorodia, for the period 1992-2010. During their first southward migration, most spoonbills migrated to the southernmost wintering region (Mauritania and Senegal). Other birds were likely to move there from their first to their second winter, whereas hardly any birds moved to a more northerly wintering area. For the rest of their life, spoonbills remained highly site faithful. This resulted in most birds wintering in Mauritania and Senegal with smaller numbers in France and Iberia. We judged suitability of sites on the basis of annual survival probabilities in these three wintering areas. Surprisingly, survival was lowest in Mauritania and Senegal. None of the existing fitness maximization hypotheses explain this pattern and we discuss potential alternatives. Wintering site choice could still be optimal for individual birds if birds wintering in Mauritania and Senegal are competitively inferior to the European winterers or more susceptible to severe winter weather. Alternatively, wintering site choice of spoonbills is suboptimal and, assuming that spoonbills can assess differences in suitability, limited flexibility may prevent them from switching to more suitable sites. © 2011 The Association for the Study of Animal Behaviour.


Lok T.,University of Groningen | Lok T.,Netherlands Institute for Sea Research | Overdijk O.,Werkgroep Lepelaar | Piersma T.,University of Groningen | Piersma T.,Netherlands Institute for Sea Research
Biology Letters | Year: 2015

Explanations for the wide variety of seasonal migration patterns of animals all carry the assumption that migration is costly and that this cost increases with migration distance. Although in some studies, the relationships between migration distance and breeding success or annual survival are established, none has investigated whether mortality during the actual migration increases with migration distance. Here, we compared seasonal survival between Eurasian spoonbills (Platalea leucorodia leucorodia) that breed in The Netherlands and migrate different distances (ca 1000, 2000 and 4500 km) to winter in France, Iberia and Mauritania, respectively. On the basis of resightings of individually marked birds throughout the year between 2005 and 2012, we show that summer, autumn and winter survival were very high and independent of migration distance, whereas mortality during spring migration was much higher (18%) for the birds that wintered in Mauritania, compared with those flying only as far as France (5%) or Iberia (6%). As such, this study is the first to show empirical evidence for increased mortality during some long migrations, likely driven by the presence of a physical barrier (the Sahara desert) in combination with suboptimal fuelling and unfavourable weather conditions en route. © 2015 The Authors.


Piersma T.,University of Groningen | Piersma T.,Netherlands Institute for Sea Research | Van Der Velde M.,University of Groningen | El-Hacen E.-H.M.,University of Groningen | And 3 more authors.
Ardea | Year: 2012

In 1974 R. de Naurois and F. Roux proposed that the distinct morphology of Eurasian Spoonbills Platalea leucorodia breeding on offshore islands in the Banc d'Arguin, Mauritania, in comparison with the sympatrically wintering northwest European breeding Spoonbills Platalea leucorodia leucorodia, justifies recognition as a separate subspecies Platalea leucorodia balsaci. This proposal is examined here on the basis of variation in nuclear DNA, microsatellites identified earlier for P. minor and P ajaja. We show that there is significant variation between Spoonbills breeding in Mauritania (n = 25) and the sympatrically wintering conspecifics breeding in the Dutch Wadden Sea (n = 105). Of the total genetic variation among the 130 individuals, 6.3% is attributable to variation between the two breeding areas (93.7% of the variation is within breeding areas). Pairwise FST values showed low genetic differentiation (FST'S < 0.012) among breeding colonies within The Netherlands. The level of genetic differentiation indicates that the level of gene flow between The Netherlands and Mauritania is much lower (∼4-5 individuals/generation) than among the Dutch colonies on separate Wadden Sea islands. Field observations on individually colour-marked birds from The Netherlands indeed suggest extensive dispersal within northwest Europe, with some introgression of leucorodia genes into the balsaci population. The level of microsatellite distinctiveness between sympatric populations of the two subspecies is similar to that recorded for subspecies of other migrant birds, and as such justifies the subspecies status of the Mauritanian Spoonbill.


Lok T.,University of Groningen | Lok T.,Netherlands Institute for Sea Research | Overdijk O.,Werkgroep Lepelaar | Piersma T.,University of Groningen | Piersma T.,Netherlands Institute for Sea Research
American Naturalist | Year: 2013

When populations grow or decline, habitat selection may change due to local density-dependent processes, such as site dependence and interference. In seasonally migrating animals, nonbreeding distributions may be determined through these mechanisms of density dependence, which we examine here at a hemispheric scale for a long-distance migrating bird. Using summer and winter resightings of 2,095 Eurasian spoonbills Platalea leucorodia leucorodia that were ringed in the Netherlands during 16 years of fast population growth, we show that neither site dependence nor interference fully explains their patterns of survival and winter distribution. Within their three main wintering areas, annual survival decreased with an increase in population size. While survival was consistently higher in the two European wintering areas (France, Iberia), most spoonbills migrated onward to winter in west Africa. The number of birds wintering in Europe increased, but not enough to maximize annual survival. We conclude that a constraint of tradition (their "migration tendency") inhibits birds from changing their migratory habits. We pose that this phenomenon may similarly constrain other migratory populations from rapidly responding to large-scale climate- and/or human-driven habitat changes at their wintering grounds. © 2013 by The University of Chicago.


Lok T.,University of Groningen | Lok T.,Netherlands Institute for Sea Research | Overdijk O.,Werkgroep Lepelaar | Tinbergen J.M.,University of Groningen | And 2 more authors.
Ecology | Year: 2013

Density dependence in vital rates is key to population regulation. Rather than being constant, the strength of density dependence may vary throughout the year, but empirical evidence is limited. Based on 22 years of data of color-banded birds from a recovering population of Eurasian Spoonbills Platalea leucorodia leucorodia, we show, for the first time, seasonal variation in density dependence in survival of a long-distance migrating bird. Combining resightings and dead recoveries at breeding, stopover, and nonbreeding areas enabled us to (1) separate true survival from permanent emigration from the breeding area, and (2) estimate survival in three seasons: summer, early winter (including autumn migration), and late winter (including spring migration). Accompanying the rapid population growth, juvenile annual survival initially increased, manifested in early winter, but thereafter, at high population sizes, it strongly decreased through a combination of decreasing survival in all seasons. Annual survival of subadult (second- and third-year) and adult birds decreased more gradually with increasing population size, with density dependence occurring in early winter for subadults and late winter for adults. Thus, the shape and strength of density dependence in survival varied with age and season. Understanding the seasonal timing of density dependence, especially with reference to underlying mechanisms, is important for the design of effective conservation strategies. © 2013 by the Ecological Society of America.


El-Hacen E.-H.M.,University of Groningen | El-Hacen E.-H.M.,British Petroleum | Overdijk O.,Werkgroep Lepelaar | Lok T.,University of Groningen | And 4 more authors.
Waterbirds | Year: 2013

Mauritanian Spoonbills (Platalea leucorodia balsaci) only breed at Banc d'Arguin, Mauritania, West Africa. Their populations have declined; however, nothing is known about possible ecological factors involved, including their primary food and foraging habits. Home range sizes, habitat selection, and foraging rhythm in six adult Mauritanian Spoonbills were documented by attaching backpack harnesses with solar-powered satellite GPS-transmitters. Based on 18 bird-months of data (5,844 selected ground positions) collected between 2008 and 2010, these individuals never left the study area centered on the island of Tidra. The fixed kernel home range size was 23-101 km2 ( = 62 km 2) and the core area 2-14 km2 ( = 7 km2). Home range sizes did not differ between breeding and non-breeding seasons. Mauritanian Spoonbills fed only in intertidal areas where they preferred the seagrass-covered (Zostera noltii) areas and they fed primarily during the ebbing tide. Furthermore, the GPS-positions away from the high tide roosts were strongly associated with creeks dissecting the seagrass beds. During the non-breeding season, foraging occurred throughout the 24-hr period, but during the breeding season they foraged exclusively by night.


Lok T.,University of Groningen | Lok T.,Netherlands Institute for Sea Research | Overdijk O.,Werkgroep Lepelaar | Piersma T.,University of Groningen | Piersma T.,Netherlands Institute for Sea Research
Ardea | Year: 2014

Chick body condition can be a sensitive indicator of local environmental conditions and has been shown to be correlated with chick survival. Designing a reliable index of chick body condition for a given species from a single measurement point requires knowledge about the extent of variation in body size, about chick age and about the relative sensitivity of the growth of different biometric measures to variation in environmental conditions. To gain this knowledge, we describe sex-specific variation in growth of several morphometric measures and body mass of Eurasian Spoonbills Platalea leucorodia. We repeatedly measured 35 chicks that grew up in small colonies on the island of Schiermonnikoog to derive detailed growth curves until fledging (based on the 12 surviving chicks) and to assess the extent of reduction in growth of starved chicks measured at least twice (n = 11) compared to those that survived. Growth curves until fledging were compared with biometric measurements of two to five week old chicks from (mostly) larger colonies of which hatching date was accurately estimated (n = 631). Growth of all measures, except the eighth primary, was sex-specific, with the most pronounced sex effect on the asymptotic values of tarsus length and body mass: adult males were predicted to become 17% heavier than females and to have 22% longer tarsi than females. Body mass and tarsus growth tended to be more reduced under food deprivation than (head-)bill and eighth primary growth. As an index of chick body condition, we propose to use the proportional deviation in body mass from the predicted body mass for a given age and sex. To do so, measurements of nearly fledged Spoonbill chicks should include at least eighth primary length to estimate age, tarsus length to estimate sex, and body mass as a measure that integrates age, sex and environmental effects.


El-Hacen E.-H.M.,University of Groningen | Piersma T.,University of Groningen | Piersma T.,Netherlands Institute for Sea Research | Jouta J.,University of Groningen | And 4 more authors.
Journal of Ornithology | Year: 2014

We used stable isotope tracers in the growing primary feathers of Eurasian Spoonbill chicks (Platalea leucorodia leucorodia) to study seasonal variation in their diet on one of the Frisian islands, Schiermonnikoog, The Netherlands. Using growing individual primaries as natural samplers over time, samples were taken along the length of primary feathers to estimate both within- and between-individual variation in diet. Absolute isotopic ratios of feather material ranged from -26.2 to -14.7 ‰ for carbon (δ13C) and from 13.0 to 18.7 ‰ for nitrogen (δ15N). The variation in δ13C values suggests the use of a variety of feeding habitats, ranging from freshwater to marine. Across the breeding season, there was a shift from predominantly freshwater prey early on to a more marine diet later in the season. Surprisingly, this shift did not occur within the growth trajectory of early born chicks which instead showed the opposite, but it did occur within individual chicks born later in the season. Stable isotope Bayesian mixing-model (SIAR) outcomes demonstrated that the freshwater/brackish prey had the highest isotopic contribution (51 %; 95 % confidence interval 39-63 %) to the diet early in the breeding season, whereas marine prey contributed most (78 %; 66-89 %) to the diet later. That chicks fed with either freshwater or marine food items had similar body condition indices suggests that the eating of marine prey did not come at a major cost for growing Spoonbill chicks. © 2014 Dt. Ornithologen-Gesellschaft e.V.


PubMed | University of Groningen and Werkgroep Lepelaar
Type: Journal Article | Journal: Ecology | Year: 2013

Density dependence in vital rates is key to population regulation. Rather than being constant, the strength of density dependence may vary throughout the year, but empirical evidence is limited. Based on 22 years of data of color-banded birds from a recovering population of Eurasian Spoonbills Platalea leucorodia leucorodia, we show, for the first time, seasonal variation in density dependence in survival of a long-distance migrating bird. Combining resightings and dead recoveries at breeding, stopover, and nonbreeding areas enabled us to (1) separate true survival from permanent emigration from the breeding area, and (2) estimate survival in three seasons: summer, early winter (including autumn migration), and late winter (including spring migration). Accompanying the rapid population growth, juvenile annual survival initially increased, manifested in early winter, but thereafter, at high population sizes, it strongly decreased through a combination of decreasing survival in all seasons. Annual survival of subadult (second- and third-year) and adult birds decreased more gradually with increasing population size, with density dependence occurring in early winter for subadults and late winter for adults. Thus, the shape and strength of density dependence in survival varied with age and season. Understanding the seasonal timing of density dependence, especially with reference to underlying mechanisms, is important for the design of effective conservation strategies.

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