Fueling Incubation: Differential Use of Body Stores in Arctic and Temperate-breeding Barnacle Geese (Branta leucopsis)

We compared the use of body stores in breeding Barnacle Geese (Branta leucopsis) in traditional Arctic colonies in the Barents Sea with that in recently established temperate-zone breeding colonies in the Baltic Sea and North Sea by studying female body-mass loss and use of fat and protein stores during incubation. Average daily body-mass loss was almost identical in the 2 temperate-breeding populations (17.0 g and 16.5 g in Baltic Sea and North Sea, respectively), whereas Arctic-breeding females lost significantly less (10.6 g day-1). Temperate-breeding females initiated incubation with body mass 125 g higher than that of Arctic breeders, but at the end of incubation, body mass was similar among the 3 populations, averaging 1,458 g. Body-mass loss during incubation amounted to 23% (North Sea), 22% (Baltic Sea), and 15% (Barents Sea). Fat mass, as measured by isotope dilution in a subsample of females, was consistently higher in North Sea than in Barents Sea birds, but both populations showed similar rates of fat-mass loss (9.4 g day-1, on average). By contrast, loss of fat-free mass (assumed to represent wet protein) amounted to 9.3 g day-1 in North Sea birds but only 1.5 g day-1 in Barents Sea birds. Energy content of 1 g utilized body mass was 21.1 kJ (North Sea) and 34.9 kJ (Barents Sea), which equates to 376 kJ day-1 and 415 kJ day-1 drawn from stored energy, respectively. We suggest that differences in nest-attendance and post-incubation demands are responsible for the differential use of body stores in temperate- and Arctic-breeding Barnacle Geese.

Are Dutch Skylarks partial migrants? Ring recovery data and radio-telemetry suggest local coexistence of contrasting migration strategies

In recent years, Skylarks Alauda arvensis have undergone dramatic population declines in many European countries. Evidence exists for deteriorating conditions during the breeding season, but little is known about the situation during the rest of the annual cycle. Here we use two approaches to test if the Dutch breeding population of Skylarks consists of resident and/or migratory individuals. First, we present an analysis of ring recoveries from the Dutch Ringing Centre "Vogeltrekstation". Out of 25 recoveries, 12 Skylarks were resident in winter, 10 migrated and three were classified as probable migrants. Resident birds were accompanied during winter by birds from northern and eastern Europe. Very limited natal and breeding dispersal recorded in the same dataset suggests that our results were not influenced by long dispersal distances. Next, we compared these results to a local radio-telemetry study in the northern Netherlands. During two different years we equipped a total of 27 Skylarks from a breeding population with radio-transmitters and followed them during the subsequent winter. Four birds were found to winter locally. Out of 23 individuals that we did not find in winter, 14 returned in the following breeding season to the study area, all with a working transmitter, suggesting that they wintered outside our study area. Two ring recoveries of birds from the same study population indeed showed migration to south-west Europe. Based on these two lines of evidence, we conclude local coexistence of a resident and a migrant strategy in Dutch Skylarks. The findings of our study are important for the planning of conservation efforts, as we can only protect this rapidly declining species when we know their behaviour and whereabouts throughout the entire annual cycle

Demographic Changes Underpinning the Population Decline of Starlings Sturnus vulgaris in the Netherlands

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Evaluatie Opvangbeleid 2005-2008 overwinterende ganzen en smienten. Deelrapport 12. Effecten van grootte, vorm en ligging van ganzenfoerageergebieden op de opvangcapaciteit

Vanaf 2005 zijn in Nederland foerageergebieden aangewezen waarin ganzen worden geconcentreerd teneinde schade aan landbouwgewassen buiten deze gebieden te verminderen. Binnen de foerageergebieden wordt zo veel mogelijk rust en voldoende voedsel aangeboden, buiten deze gebieden worden ganzen verjaagd, al dan niet ondersteund door afschot. De randen van de aangewezen foerageergebieden zijn soms grillig en rafelig, en binnen de aangewezen foerageergebieden kunnen enclaves voorkomen omdat individuele boeren niet meedoen aan de regeling. Dit leidt mogelijk tot een niet optimaal gebruik van de foerageergebieden door ganzen. Daarom is de opvangcapaciteit in relatie tot de grootte, de vorm en de ligging van de foerageergebieden onderzocht

Large-Scale Changes in Community Composition: Determining Land Use and Climate Change Signals

Human land use and climate change are regarded as the main driving forces of present-day and future species extinction. They may potentially lead to a profound reorganisation of the composition and structure of natural communities throughout the world. However, studies that explicitly investigate both forms of impact—land use and climate change—are uncommon. Here, we quantify community change of Dutch breeding bird communities over the past 25 years using time lag analysis. We evaluate the chronological sequence of the community temperature index (CTI) which reflects community response to temperature increase (increasing CTI indicates an increase in relative abundance of more southerly species), and the temporal trend of the community specialisation index (CSI) which reflects community response to land use change (declining CSI indicates an increase of generalist species). We show that the breeding bird fauna underwent distinct directional change accompanied by significant changes both in CTI and CSI which suggests a causal connection between climate and land use change and bird community change. The assemblages of particular breeding habitats neither changed at the same speed and nor were they equally affected by climate versus land use changes. In the rapidly changing farmland community, CTI and CSI both declined slightly. In contrast, CTI increased in the more slowly changing forest and heath communities, while CSI remained stable. Coastal assemblages experienced both an increase in CTI and a decline in CSI. Wetland birds experienced the fastest community change of all breeding habitat assemblages but neither CTI nor CSI showed a significant trend. Overall, our results suggest that the interaction between climate and land use changes differs between habitats, and that comparing trends in CSI and CTI may be useful in tracking the impact of each determinant

Postnatal growth rate varies with latitude in range-expanding geese: The role of plasticity and day length

1. The postnatal growth period is a crucial life stage, with potential lifelong effects on an animal's fitness. How fast animals grow depends on their life‐history strategy and rearing environment, and interspecific comparisons generally show higher growth rates at higher latitudes. However, to elucidate the mechanisms behind this gradient in growth rate, intraspecific comparisons are needed. 2. Recently, barnacle geese expanded their Arctic breeding range from the Russian Barents Sea coast southwards, and now also breed along the Baltic and North Sea coasts. Baltic breeders shortened their migration, while barnacle geese breeding along the North Sea stopped migrating entirely. 3. We collected cross‐sectional data on gosling tarsus length, head length and body mass, and constructed population‐specific growth curves to compare growth rates among three populations (Barents Sea, Baltic Sea and North Sea) spanning 17° in latitude. 4. Growth rate was faster at higher latitudes, and the gradient resembled the latitudinal gradient previously observed in an interspecific comparison of precocial species. Differences in day length among the three breeding regions could largely explain the observed differences in growth rate. In the Baltic, and especially in the Arctic population, growth rate was slower later in the season, most likely because of the stronger seasonal decline in food quality. 5. Our results suggest that differences in postnatal growth rate between the Arctic and temperate populations are mainly a plastic response to local environmental conditions. This plasticity can increase the individuals' ability to cope with annual variation in local conditions, but can also increase the potential to re‐distribute and adapt to new breeding environments

Reduced avian body condition due to global warming has little reproductive or population consequences

Climate change has strong effects on traits such as phenology and physiology. Studies typically assume that climate-induced trait changes will have consequences for population dynamics, but explicit tests are rare. Body condition reflects energy storage and may directly affect how much can be invested in reproduction and survival. However, the causal pathway by which decreased body condition impacts population dynamics has never been quantified across multiple populations and species. Therefore, we lack a general understanding of the consequences of changes in condition for variables more relevant for conservation, such as population size. Using structural equation modeling, we investigate how temperature-induced changes in body condition affect reproduction, and the subsequent impact on population growth rates of 19 bird species across 80 Dutch sites over a 21-year period. Warmer temperatures were associated with decreased body condition, which led to both decreased and increased reproduction at different sites, cancelling out any overall effect. The indirect effect of temperature on population growth (via body condition and reproduction) only explained within-species variation in the total effects of temperature on population growth. Instead, the direct effect of temperature on population growth (unrelated to condition and reproduction) was the most important pathway underlying the total effects of temperature on population growth, suggesting that unknown variables are mediating this effect. About half of the species are expected to increase under global warming, but this variation was not associated with any species characteristic. Overall, body condition responses to global warming are common, but their consequences on reproduction and subsequently population growth contribute relatively little to the total temperature impacts on population dynamics. Given that warming temperatures have strong effects on population dynamics, understanding the pathways via which temperature impacts population dynamics will be crucial for our ability to predict climate change effects in the future and improve conservation efforts