Oystercatchers moving with the tides: site-fidelity in a dynamic environment

Adriaan M. Dokter¹, Martin J. Baptist², Willem Bouten¹, Bruno J. Ens³, Kees Oosterbeek³, Cornelis Rappoldt⁴, E. Emiel van Loon¹

¹ Institute for Biodiversity and Ecosystem Dynamics, University of Amsterdam, The Netherlands

² IMARES Wageningen UR, Den Hoorn, Texel, Netherlands

³ SOVON Dutch Centre for Field Ornithology, Coastal Ecology Team, Den Burg, Texel, The Netherlands

⁴ Ecocurves, Haren, The Netherlands

 

Knowing the spatio-temporal distribution of foraging shorebirds is of basic relevance to policy and managing of intertidal areas. But which of the multitude of factors that have been shown to affect shorebird foraging, are most relevant for explaining spatial distributions?

Generalised functional response models may be considered the standard null model of shorebird distribution.  They have been used to predict the spatial distribution of birds given their distribution of food, under the assumptions that birds attempt to maximize intake rate as a short-term fitness objective and behave as ideal and free predators. Remarkably few quantitative assessments of the degree of applicability of these models to free-living shorebirds exist for real intertidal systems. An important aspect preventing quantitative comparisons with model predictions has been the lack of observational data that covers the typically extensive foraging home ranges, as well as the relevant temporal cycles (tidal, diurnal, seasonal) that affect spatial distribution and food availability.

We used GPS-tracking individual free-living Oystercatchers to quantify how Oystercatchers distribute themselves in relation to the tidal cycle and their food. High-resolution benthic surveys were carried out in the core foraging areas of focal individuals. The study permits a comparison of observed and predicted spatial distribution and food depletion, and identifies key factors governing the spatio-temporal distributions (focussing on association with intake rate, interference effects, and tide line effects). We argue that the benefits associated with a high site fidelity, as observed in the Eurasian Oystercatcher, may lead to a weaker association with patch quality than predicted by ideal free models.

 

 

 

Foraging behavior of Caspian terns breeding in Sweden as tracked by GPS loggers

Kozue Shiomi¹, Henri Engström², Tom Evans¹, Ulrik Lötberg², Willem Bouten³, Judy Shamoun-Baranes³, and Susanne Åkesson¹

¹ Centre for Animal Movement Research (CAnMove), Department of Biology, Lund University, Sweden

² Swedish Ornithological Society, Mörbylånga Sweden

³ Institute for Biodiversity and Ecosystem Dynamics, University of Amsterdam, The Netherlands

 

The Caspian tern (Hydroprogne caspia) is the largest tern species, which has a wide breeding distribution throughout the world. In Sweden, the largest breeding colony of this species is the small island of Norra Stenarna, at Fågelsundet in the Baltic Sea (N 60° 37’ 53”, E 17° 55’ 46”) with about 100 breeding pairs every year in the last three years. The investigation of the foraging habitat of these large populations is important not only for improved understanding of their breeding biology but also for conservation of the species. To obtain movement paths during foraging trips and to collect data on foraging sites throughout the season, we deployed GPS data loggers (<7.5 g in mass, UvA-BiTS) with Teflon ribbon harness on seven Caspian terns breeding at Norra Stenarna. The loggers recorded time-series positional data at 2.5 min or 5 min of sampling intervals. Foraging areas were estimated based on ground speeds calculated from consecutive positional fixes. Histograms of the speeds were bimodal; one peak value was near zero, and the other around 38 to 42 km h^-1. The higher values were considered as average flight speeds, while the lower ones corresponded with resting or foraging events. We will discuss distribution of estimated foraging areas in relation to breeding stages and individual differences in foraging habitat selection.

 

 

 

Brent geese in a meta-ecosystem: spatial movements & the relations with ecological factors

W. Fokkema¹, Adriaan M. Dokter², Bart S. Ebbinge ³, Bart A. Nolet ², Han Olff ¹, Henk P. van der Jeugd ²

¹ Community and Conservation Ecology, Centre for Ecological and Evolutionary Studies, University of Groningen, The Netherlands

² Netherlands Institute of Ecology (NIOO-KNAW), Wageningen, The Netherlands

³ Team Animal Ecology, Alterra, Wageningen-UR, The Netherlands

 

Migrating species connect ecosystems and the species present in those ecosystems. This causes that changes in one ecosystem can be carried over to other ecosystems, used by the same species. The Waddensea for example is connected to several ecosystems via different migrating bird species. In Metawad the role of the Waddensea as well as the ecology of several of these bird species is being investigated.

The dark-bellied brent goose (Branta bernicla bernicla) is a herbivorous bird which breeds in Siberia and winters in France and Southern England. The Waddensea serves as an important spring staging area. The preferred food resource of brent geese is seagrass. Seagrasses are present in the wintering areas and in many of the staging areas. The Dutch Waddensea is an exception, because seagrasses are hardly present there. In this area, brent geese have switched to either (low) salt marshes or pastures.

We study how brent geese are making use of the meta-ecosystem along their flyway. In spring 2012, 30 brent geese have been equipped with UvA-bits GPS loggers. 21 of those were caught in a polder area on the island of Terschelling. Those geese are mainly using pastures in the Waddensea area. 9 were caught on the low salt marsh of Schiermonnikoog. Those birds are mainly using the salt marsh areas of the Waddensea. Our results show that certain areas serve as ‘hotspots’ for either individuals or for most of the tracked birds. By using existing (GIS) data and the results of an intensive sampling program on both Terschelling and Schier, we relate the preferred areas to specific (a)biotic conditions and the presence of food resources, like seagrasses. These patterns are analyzed both at local scales and at the scale of the whole flyway. Both birds which were caught on pastures, as birds caught on salt marshes, mainly use seagrass beds in their wintering areas. On local scale (the salt marsh of Schiermonnikoog) brent geese showed more data points on the most saline spots of the salt marshes. This can be for competitive reasons, but also the physiology of the plants which are being eaten can play an important role. Finally, from the tracks it can be derived how brent geese are creating a network of habitats. This on its turn can give an insight in the connection between ecosystems at different scales.

 

 

 

Black-tailed Godwit Habitat Use in Agricultural Landscapes During the Pre-Migratory Period: What Really Matters?

Nathan Senner¹, Mo Verhoeven¹, Jos Hooijmeijer¹, Heije Hoekema¹, and Theunis Piersma¹

¹ Animal Ecology, Centre for Ecological and Evolutionary Studies, Groningen University, The Netherlands

 

Black-tailed Godwits breeding in The Netherlands have rapidly declined during recent decades. This decline has largely been linked to the effects of agricultural intensification on their reproductive success. Adult Black-tailed Godwits also use agricultural habitats throughout much of the rest of their annual cycle, however, and agricultural intensification during these periods may have an effect on godwit population dynamics as well. Previous work has identified a shift in the timing of godwit post-breeding migration to Iberia and West Africa — with unknown fitness consequences — and this shift may be linked with habitat use during their migratory preparation. In order to link events and habitats throughout the annual cycle, we attached 20 UvA-BiTS transmitters to female godwits breeding in Southwest Friesland in the 2013 breeding season. Following completion of the nesting season, we launched preliminary efforts to categorize the habitats used by these individuals, as well as to monitor their foraging effort and characterize at a broad scale the resource abundance and agricultural status of these habitats. Our initial results suggest that adult godwits predominantly use intensively managed meadows during this period and that the timing of mowing in the region may drive their use of specific meadows. However our measurements of resource abundance and foraging effort indicate that these choices may not be optimal. Given these intriguing possibilities, our work will now focus on creating season-long energy budgets for individual godwits and linking these with fine-scale resource mapping. Combined, we hope to better understand the optimal landscape structure for Black-tailed Godwits.

 

 

 

Sexually distinct foraging strategies and individual specialization of Lesser Black-backed gulls

Judy Shamoun-Baranes¹, Kees Camphuysen², Emiel van Loon¹, Chris Tyson¹, Willem Bouten¹

¹ Institute for Biodiversity and Ecosystem Dynamics, University of Amsterdam, The Netherlands

² Royal Netherlands Institute for Sea Research (NIOZ), Texel, The Netherlands

 

Sex, age, morphology and individual specialization may all contribute to intra-specific differences in foraging behavior, which may influence an individual’s fitness. Lesser Black-backed gulls (Larus fuscus) are opportunistic seabirds, with a broad omnivorous diet. We examined the influence of breeding status and sex on the foraging behavior of Lesser Black-backed gulls by combining GPS tracking data from 34 individuals and 2199 foraging trips, with information on diet and breeding status collected in a breeding colony on a Wadden Sea island in the Netherlands. We found sexually distinct foraging strategies that were maintained throughout incubation and chick-care. Larger males travelled farther from the colony than females, spent more time in the North Sea, feeding mostly on fishery discards at offshore trawlers and remained longer at the nest during nest visits. In general, females foraged predominantly on land or in the Wadden Sea. Females that foraged in the Waddem sea were clearly specializing on fishery activities.  They spent significantly more time in the Wadden Sea on weekdays compared to weekends, and were tracked almost exclusively within deep gullies, following the temporal and spatial patterns of the shrimp fisheries in the area. On weekends, when trawlers were inactive, Wadden Sea specialists spent relatively more time in terrestrial habitats. A combination of individual specialization and sexually distinct foraging strategies during breeding, as shown in this study, may increase an individual’s lifetime reproductive success by reducing resource competition between sexes (and within pairs) or through risk partitioning, neither of which is mutually exclusive.

 

 

 

Central-place foraging flights of lesser black-backed gull under varying meteorological conditions

Tom J. Evans¹ , Judy Shamoun-Baranes², Willem Bouten² , Anders Hedenström¹, Susanne Åkesson¹

¹ Centre for Animal Movement Research (CAnMove), Department of Biology, Lund University, Sweden

² Institute for Biodiversity and Ecosystem Dynamics, University of Amsterdam, The Netherlands

 

Seabirds typically breed at high density, foraging over a wide surrounding area, i.e. central-place foraging. We study a species, the lesser black-backed gull Larus f. fuscus, with a mixed strategy of pelagic marine and land based foraging in the Baltic Sea. Using high resolution GPS tracking we followed gulls throughout the breeding period. We obtained detailed movement data, including positions, flight speeds, altitude, and for some of the data three-axis accelerometer measurements.  Foraging flights are analysed with respect to varying conditions (e.g. wind), measuring the consequences and counter-strategies of the gulls. For example, on the inward flight of a marine foraging trip the gulls are expected to perform goal-orientated movement (i.e. they should return directly to the nest site). However, wind conditions will vary during foraging trips, such that on some flights they may experience cross-winds, in the absence of mechanisms to detect these, longer less direct flights would be performed. If the gulls are able to detect lateral movement resulting from wind-drift, they should perform more direct flights. Our dataset allow us to analyse flights for many individuals under a wide range of conditions, thus determining their individual flight strategies. Depending on cues used to detect, and compensate for drift, the extent of wind-drift may differ under different sky conditions. If sky cues are important, then drift may be greater under overcast skies than clear skies.

 

 

 

Tracking lesser black-backed gulls through the year reveals annual, seasonal, and individual variation in seabird-wind farm interactions

Chris Thaxter¹, Viola Ross-Smith¹, Willem Bouten², Nigel Clark¹, Greg Conway¹, Ali Johnston¹ and Niall Burton¹.

¹ British Trust for Ornithology, Norfolk, United Kingdom.

² Institute for Biodiversity and Ecosystem Dynamics, University of Amsterdam, The Netherlands.

 

The marine environment is under increasing pressure from human activities, including offshore renewable energy developments. This project uses UvA-BiTS technology to investigate the potential impacts of such developments on a breeding population of Lesser Black-backed Gulls. We examined the consequences of: (1) seasonal, (2) annual and (3) individual variation in habitat use by birds (4) the “connectivity” between breeding populations and offshore developments during the non-breeding season, and (5) the flight altitude to model the likelihood of collision risk with wind turbines.

During 2010 and 2011, we deployed 25 long-life GPS loggers to Lesser Black-backed Gulls breeding at the Alde-Ore Estuary Special Protection Area (SPA) in southeast England, located nearby to existing, consented and proposed offshore wind farms, to understand patterns of movement through three breeding seasons (2010, 2011, and 2012) and subsequent migration and wintering periods. Flight altitudes were modelled using a Bayesian framework. For horizontal movements, a general mixed effects modelling approach was used to assess the variation in habitat use and extent of wind farm area overlaps.

The data collected by this study have enabled the potential exposure of this specific protected population to the risks associated with offshore developments to be quantified not just within the breeding season, but across the year.

 

 

 

Individual variation in habitat use and home range size of Dutch Montagu’s Harriers

Raymond H.G. Klaassen^1,2, Almut Schlaich^1,2,Christiaan Both², Willem Bouten³, Ben J. Koks¹

¹ Dutch Montagu’s Harrier Foundation, Scheemda, The Netherlands

² Animal Ecology, Centre for Ecological and Evolutionary Studies, Groningen University, The Netherlands

³ Institute for Biodiversity and Ecosystem Dynamics, University of Amsterdam, The Netherlands

 

In nature ‘the average bird’ does not exist as individuals differ in their behaviour. With UvA-BiTS GPS-loggers it has now become possible to study individual behaviour in unprecedented detail. We tracked male Montagu’s Harriers Circus pygargus in order to study home ranges and habitat use at a daily scale during the breeding season. This revealed that individual harriers have very different strategies in how they use the landscape. In particular, some individuals concentrate foraging efforts in a limited number of fields, which they revisit almost every day. In contrast, other individuals are more mobile and use a much larger number of fields, which they revisit much less frequently. Individuals with contrasting landscape use strategies live in the same general area, indicating that differences in behaviour represent different individual traits. These results are relevant for planning the spatial configuration of favourable foraging habitat (set-aside habitats), an important conservation measure for Montagu’s Harriers.

 

 

 

Space use, activity patterns and hunting behaviour of Verreaux’s eagle in the Western Cape, South Africa

Theoni Photopoulou^1,2, Megan Murgatroyd², Les Underhill², Andrew Jenkins³ and Res Altwegg¹

¹ Department of Statistical Sciences, University of Cape Town, South Africa

² Animal Demography Unit, University of Cape Town, South Africa

³ AVISENSE Consulting, 10 Harrier Circle, South Africa

 

UvA-BiTS telemetry devices were deployed on five Verreaux’s eagles to investigate their activity patterns, ranging patterns and hunting behaviour, as part of a broader study into their breeding ecology and conservation status. Two birds were tagged in the Cederberg Mountains, and three in the adjacent agriculturally transformed Sandveld area in 2012 and 2013 in the Western Cape of South Africa. The GPS location data revealed dynamic overturn of territory ownership, and larger scale movement than previously known for an individual that was ousted from its territory. Statistical methodology is being developed for the analysis of activity patterns using the acceleration data. We propose initially to use a flexible two-state mechanistic model, which can incorporate additional behavioural information. We are also developing a model for detecting hunting events using speed and acceleration information, to help identify the spatial and temporal distribution of hunting behaviour.

 

 

 

Getting to grips with the very first phase of analyzing animal trajectory data

Emiel van Loon¹, Judy Shamoun-Baranes¹ and Willem Bouten¹

¹ Institute for Biodiversity and Ecosystem Dynamics, University of Amsterdam, The Netherlands

 

The initial step to analyze UvA-BiTS trajectory data consist of data retrieval, followed by some form of screening and the production of summary statistics and graphs to decide which data is relevant for the questions at hand. Whether we like it or not, many impactful pre-processing decisions have to be made already from the start. Examples of such decisions are are: which data to include (e.g. individuals, time-window, anomalous trajectories), what aggregation level to choose, how to define important concepts (e.g. what is a trajectory, what is a repeated visit), and how to calculate derived properties (e.g. distance traveled, time spent flying). Unfortunately it is very hard to predict the consequences of these decisions during data pre-processing on subsequent analyses.

After providing quantitative evidence that analyses of trajectory data are quite sensitive to the aforementioned pre-processing decisions, this presentation provides guidelines, supported by software, to deal with three important decisions and data pre-processing steps: 1) choosing the best level of aggregation in your analysis, 2) dealing with irregular sampling intervals and homogenizing your data set, and 3) setting appropriate thresholds for excluding inappropriate data. The practical application of these guidelines is demonstrated on two data sets. An open question is how to establish the entire range of analysis questions and types of data where the proposed guidelines and supporting software would be effective and above all not biasing the results. An experimental plan to achieve this is outlined, but above all we would welcome careful application of the guidelines in as many cases as possible.

 

 

 

Evolution of space use of translocated juvenile Red Kites (Milvus milvus)

Willem Bouten¹ , Daan Aerts¹, Emiel van Loon¹, Judy Shamoun-Baranes¹, Guido Ceccolini² and Anna Cenerini ^2
1 Institute for Biodiversity and Ecosystem Dynamics, University of Amsterdam, The Netherlands

² CERM Endangered Raptors Centre, Italy

 

The establishment and persistence of re-introduced or re-stocked populations of scavengers is generally supported by the supply of food at feeding stations. However, it is often unclear how such a predictable food resource influences habitat use, landscape exploration, dispersal, survival, reproduction and self-sustained independency of these birds.  Using GPS loggers, measuring 100 positions per day throughout the first year after release, we studied habitat use and dispersal of 13 juvenile Red Kites (Milvus milvus) that were captured from their nests in Corsica and Switzerland and translocated to Tuscany, Italy in August 2012. The evolution of calculated movement characteristics varies considerably among individuals. While most released individuals relied on food supply during winter, some individuals could sustain themselves for periods up to 50 days with no (or almost no) feeding station visits. Long trips with flight distances of over 250 km per day and maximum separation of more than 350 km from the feeding station occurred during good thermal conditions from April to July. Deceasing frequency of feeding station visits, increasing distance between roost sites and the feeding station, and an increasing number of long trips were interpreted as a decreasing dependency on food supply and an increasing tendency for space exploration. Interestingly, most of the heavily exploited patches identified in this study are not in the Natura 2000 special protection areas although the feeding station is located at the border. This years, monitoring is extended by tagging individuals from different age classes to further investigate the evolution of self-reliance.

 

 

 

Wind-dependent foraging flights of Eleonora’s falcons on Alegranza

Laura Gangoso¹, D. S. Viana¹, Willem Bouten² and Jordy Figuerola¹

¹ Department of Wetland Ecology, Estación Biológica de Doñana, CSIC, Avda Américo Vespucio s/n E-41092, Seville, Spain

² Institute for Biodiversity and Ecosystem Dynamics, University of Amsterdam, The Netherlands

 

Ecological specialization to fluctuating resources entails important costs, such as those deriving from phenological mismatches between the feeding necessities of migratory animals and their resources. The Eleonora’s falcon (Falco eleonorae) is a long-distance migratory raptor that breeds over the entire Mediterranean basin. During the breeding season, Eleonora’s falcons feed primarily on small birds migrating from Europe to Africa, and thus breeding colonies are strategically situated in small and isolated islands located along the main migratory routes, except in the Canary archipelago. In the latter islands, Eleonora’s falcons depend on migratory birds that arrive, accidentally, dragged by seasonal Eastern winds. In 2012, we tagged six adult Eleonora’s falcons breeding in the Alegranza islet (Canary Islands) to investigate how the feeding strategies of falcons are shaped by the wind patterns regulating the intensity of the bird migratory flux. By using the GPS data obtained in 2012 and 2013, as well as data from meteorological radars, we analyzed the relationship between wind patterns and the hunting movements of falcons (e.g. daily distance travelled and maximum distance from Alegranza), and their consequences for reproductive success. When trade winds were blowing, male Eleonora’s falcons did several short travels per day in search for food. However, when wind patterns were unfavorable, they traveled longer distances. During long periods of unfavorable winds, falcons moved over 300 km and reached the African continent in some occasions. In contrast, females only made short, local displacements near the nest or to the nearest fresh water source.

 

 

 

The influence of weather on soaring migration performance at multiple scales

Wouter M.G. Vansteelant¹, Willem Bouten¹, Judy Shamoun-Baranes¹, Jan van Diermen², Emiel van Loon¹ and  Willem van Maanen²

¹ Institute for Biodiversity and Ecostystem Dynamics, University of Amsterdam, the Netherlands
² Stichting Boomtop, Assen, The Netherlands

 

Tracking studies have revealed important regional and seasonal differences in the travel performance of long-distance migrants. Many species are reported to migrate faster in spring or when crossing ecological barriers and this is often interpreted as evidence for an evolutionary basis of regional and seasonal performance patterns. On the other hand, weather conditions may have a strong influence on travel performance and especially for soaring birds which spend about half their travel time in passive circle-soaring flight, at the mercy of prevailing winds.

We tracked 14 Honey Buzzards with UvA-BiTS GPS loggers covering >50 seasonal travels. We show how their cross-country performance  is affected by wind and convective conditions at three different time scales (travel days, full travel hours and soaring-gliding bouts). We use high-resolution data (interval 10 sec´s) from 4 birds to automatically classify soaring-gliding bouts after which we accurately determine wind compensation strategies in those bouts.  We finally compare how cross-country performance varies, within and between days, across seasons and bio-geographical regions, and whether weather or compensation strategies account for performance patterns.

Overall, we show that wind conditions are a dominant determinant of performance and that influence of convective conditions and crosswinds decreases at larger scales. Performance is best explained at the scale of minutes and at all scales predicted performance patterns closely match observed performance patterns. Wind compensation strategies underlie remaining variation in performance unexplained by weather, most notably in the case of the highly seasonal response of birds to weather above the Sahara.