Kees Oosterbeek

Experimental evidence for effects of human disturbance on foraging and parental care in oystercatchers

We carried out two experiments to quantify effects of human disturbance on foraging and parental care in European oystercatchers (Haematopus ostralegus). In experiment 1, pairs incubating a clutch were disturbed on their feeding territory on the mudflat. Disturbance significantly reduced the proportion of time that the clutch was incubated, but also the proportion of time that the pair spent on the mud flat. In experiment 2, foraging oystercatcher pairs with chicks were disturbed by two observers at different distances from the edge of the salt marsh where the chicks resided. Total food collected was independent of disturbance, but a smaller proportion of the food collected was allocated to the chicks with increasing disturbance level. Both experiments demonstrate that human disturbance of foraging in breeding oystercatchers reduced the amount of parental care, and thus presumably reproductive success.

From Sensor Data to Animal Behaviour: An Oystercatcher Example

Animal-borne sensors enable researchers to remotely track animals, their physiological state and body movements. Accelerometers, for example, have been used in several studies to measure body movement, posture, and energy expenditure, although predominantly in marine animals. In many studies, behaviour is often inferred from expert interpretation of sensor data and not validated with direct observations of the animal. The aim of this study was to derive models that could be used to classify oystercatcher (Haematopus ostralegus) behaviour based on sensor data. We measured the location, speed, and tri-axial acceleration of three oystercatchers using a flexible GPS tracking system and conducted simultaneous visual observations of the behaviour of these birds in their natural environment. We then used these data to develop three supervised classification trees of behaviour and finally applied one of the models to calculate time-activity budgets. The model based on accelerometer data developed to classify three behaviours (fly, terrestrial locomotion, and no movement) was much more accurate (cross-validation error = 0.14) than the model based on GPS-speed alone (cross-validation error = 0.35). The most parsimonious acceleration model designed to classify eight behaviours could distinguish five: fly, forage, body care, stand, and sit (cross-validation error = 0.28); other behaviours that were observed, such as aggression or handling of prey, could not be distinguished. Model limitations and potential improvements are discussed. The workflow design presented in this study can facilitate model development, be adapted to a wide range of species, and together with the appropriate measurements, can foster the study of behaviour and habitat use of free living animals throughout their annual routine.

FLUCTUATING SELECTION AND THE MAINTENANCE OF INDIVIDUAL AND SEX-SPECIFIC DIET SPECIALIZATION IN FREE-LIVING OYSTERCATCHERS

Fluctuating and disruptive selection are important mechanisms for maintaining intrapopulation trait variation. Nonetheless, few field studies quantify selection pressures over long periods and identify what causes them to fluctuate. Diet specialists in oystercatchers differ in short‐term payoffs (intake), but their long‐term payoffs are hypothesized to be condition dependent. We test whether phenotypic selection on diet specialization fluctuates between years due to the frequency of specialists, competitor density, prey abundance, and environmental conditions. Short‐term payoffs proved to be poor predictors of long‐term fitness payoffs of specialization. Sex‐differences in diet specialization were maintained by opposing directional fecundity and viability selection between the sexes. Contrasting other studies, selection on individual diet specialization was neither negative frequency‐ or density‐dependent nor dependent on prey abundance. Notwithstanding, viability selection fluctuated strongly (stabilizing↔disruptive) over the 26‐year study period: slightly favoring generalists in most years, but strongly disfavoring generalists in rare harsh winters, suggesting generalists cannot cope with extreme conditions. Although selection fluctuated, mean selection on specialists was weak, which can explain how individual specialization can persist over long periods. Because rare events can dramatically affect long‐term selective landscapes, more care should be taken to match the timescale of evolutionary studies to the temporal variability of critical environmental conditions.

Does agricultural food provide a good alternative to a natural diet for body store deposition in geese

Over the past decades most goose populations have become increasingly dependent on agricultural crops during wintering and migration periods. The suitability of agricultural crops to support all nutritional requirements of migratory geese for the deposition of body stores has been questioned; feeding on agricultural crops may yield higher rates of fat deposition at the cost of reduced protein accretion due to an unbalanced diet. We compared amino-acid composition of forage, and investigated food-habitat use and dynamics and composition of body stores deposited by barnacle geese feeding on agricultural pasture and in natural salt marsh during spring migratory preparation. Overall content and composition of amino acids was similar among forage from both habitats and appeared equally suitable for protein accretion. There was no relationship between body composition of geese and their preferred food habitat. Fat and wet protein contributed with 67% and 33%, respectively, to body stores gained at a rate of 11 g/d throughout the one-month study period. We found no evidence of impaired protein accretion in geese using agricultural grassland compared to natural salt marsh. Our study supports the hypothesis that the expansion of feeding habitat by including agricultural grassland has played an important role in the recent growth of the East Atlantic flyway population of barnacle geese and other herbivorous waterbirds. Feeding refuges of improved grassland provide geese with an adequate diet for the deposition of body stores crucial for spring migration and subsequent reproduction, thereby alleviating the conflict with agriculture.

Poor environmental tracking can make extinction risk insensitive to the colour of environmental noise.

The relative importance of environmental colour for extinction risk compared with other aspects of environmental noise (mean and interannual variability) is poorly understood. Such knowledge is currently relevant, as climate change can cause the mean, variability and temporal autocorrelation of environmental variables to change. Here, we predict that the extinction risk of a shorebird population increases with the colour of a key environmental variable: winter temperature. However, the effect is weak compared with the impact of changes in the mean and interannual variability of temperature. Extinction risk was largely insensitive to noise colour, because demographic rates are poor in tracking the colour of the environment. We show that three mechanisms—which probably act in many species—can cause poor environmental tracking: (i) demographic rates that depend nonlinearly on environmental variables filter the noise colour, (ii) demographic rates typically depend on several environmental signals that do not change colour synchronously, and (iii) demographic stochasticity whitens the colour of demographic rates at low population size. We argue that the common practice of assuming perfect environmental tracking may result in overemphasizing the importance of noise colour for extinction risk. Consequently, ignoring environmental autocorrelation in population viability analysis could be less problematic than generally thought.

Optimizing acceleration-based ethograms: the use of variable-time versus fixed-time segmentation

BackgroundAnimal-borne accelerometers measure body orientation and movement and can thus be used to classify animal behaviour. To univocally and automatically analyse the large volume of data generated, we need classification models. An important step in the process of classification is the segmentation of acceleration data, i.e. the assignment of the boundaries between different behavioural classes in a time series. So far, analysts have worked with fixed-time segments, but this may weaken the strength of the derived classification models because transitions of behaviour do not necessarily coincide with boundaries of the segments. Here we develop random forest automated supervised classification models either built on variable-time segments generated with a so-called ‘change-point model’, or on fixed-time segments, and compare for eight behavioural classes the classification performance. The approach makes use of acceleration data measured in eight free-ranging crab plovers Dromas ardeola.ResultsUseful classification was achieved by both the variable-time and fixed-time approach for flying (89% vs. 91%, respectively), walking (88% vs. 87%) and body care (68% vs. 72%). By using the variable-time segment approach, significant gains in classification performance were obtained for inactive behaviours (95% vs. 92%) and for two major foraging activities, i.e. handling (84% vs. 77%) and searching (78% vs. 67%). Attacking a prey and pecking were never accurately classified by either method.ConclusionAcceleration-based behavioural classification can be optimized using a variable-time segmentation approach. After implementing variable-time segments to our sample data, we achieved useful levels of classification performance for almost all behavioural classes. This enables behaviour, including motion, to be set in known spatial contexts, and the measurement of behavioural time-budgets of free-living birds with unprecedented coverage and precision. The methods developed here can be easily adopted in other studies, but we emphasize that for each species and set of questions, the presented string of work steps should be run through.

Hampered performance of migratory swans: intra- and inter-seasonal effects of avian influenza virus

The extent to which animal migrations shape parasite transmission networks is critically dependent on a migrants ability to tolerate infection and migrate successfully. Yet, sub-lethal effects of parasites can be intensified through periods of increased physiological stress. Long-distance migrants may, therefore, be especially susceptible to negative effects of parasitic infection. Although a handful of studies have investigated the short-term, transmission-relevant behaviors of wild birds infected with low-pathogenic avian influenza viruses (LPAIV), the ecological consequences of LPAIV for the hosts themselves remain largely unknown. Here, we assessed the potential effects of naturally-acquired LPAIV infections in Bewicks swans, a long-distance migratory species that experiences relatively low incidence of LPAIV infection during early winter. We monitored both foraging and movement behavior in the winter of infection, as well as subsequent breeding behavior and inter-annual resighting probability over 3 years. Incorporating data on infection history we hypothesized that any effects would be most apparent in naïve individuals experiencing their first LPAIV infection. Indeed, significant effects of infection were only seen in birds that were infected but lacked antibodies indicative of prior infection. Swans that were infected but had survived a previous infection were indistinguishable from uninfected birds in each of the ecological performance metrics. Despite showing reduced foraging rates, individuals in the naïve-infected category had similar accumulated body stores to re-infected and uninfected individuals prior to departure on spring migration, possibly as a result of having higher scaled mass at the time of infection. And yet individuals in the naïve-infected category were unlikely to be resighted 1 year after infection, with 6 out of 7 individuals that never resighted again compared to 20 out of 63 uninfected individuals and 5 out of 12 individuals in the re-infected category. Collectively, our findings indicate that acute and superficially harmless infection with LPAIV may have indirect effects on individual performance and recruitment in migratory Bewicks swans. Our results also highlight the potential for infection history to play an important role in shaping ecological constraints throughout the annual cycle.

No phenotypic plasticity in nest-site selection in response to extreme flooding events

Phenotypic plasticity is a crucial mechanism for responding to changes in climatic means, yet we know little about its role in responding to extreme climatic events (ECEs). ECEs may lack the reliable cues necessary for phenotypic plasticity to evolve; however, this has not been empirically tested. We investigated whether behavioural plasticity in nest-site selection allows a long-lived shorebird (Haematopus ostralegus) to respond to flooding. We collected longitudinal nest elevation data on individuals over two decades, during which time flooding events have become increasingly frequent. We found no evidence that individuals learn from flooding experiences, showing nest elevation change consistent with random nest-site selection. There was also no evidence of phenotypic plasticity in response to potential environmental cues (lunar nodal cycle and water height). A small number of individuals, those nesting near an artificial sea wall, did show an increase in nest elevation over time; however, there is no conclusive evidence this occurred in response to ECEs. Our study population showed no behavioural plasticity in response to changing ECE patterns. More research is needed to determine whether this pattern is consistent across species and types of ECEs. If so, ECEs may pose a major challenge to the resilience of wild populations. This article is part of the themed issue ‘Behavioural, ecological and evolutionary responses to extreme climatic events’.

Spatially detailed retrievals of spring phenology from single-season high-resolution image time series

Vegetation indices derived from satellite image time series have been extensively used to estimate the timing of phenological events like season onset. Medium spatial resolution (≥250 m) satellite sensors with daily revisit capability are typically employed for this purpose. In recent years, phenology is being retrieved at higher resolution (≤30 m) in response to increasing availability of high-resolution satellite data. To overcome the reduced acquisition frequency of such data, previous attempts involved fusion between high- and medium-resolution data, or combinations of multi-year acquisitions in a single phenological reconstruction. The objectives of this study are to demonstrate that phenological parameters can now be retrieved from single-season high-resolution time series, and to compare these retrievals against those derived from multi-year high-resolution and single-season medium-resolution satellite data. The study focuses on the island of Schiermonnikoog, the Netherlands, which comprises a highly-dynamic saltmarsh, dune vegetation, and agricultural land. Combining NDVI series derived from atmospherically-corrected images from RapidEye (5 m-resolution) and the SPOT5 Take5 experiment (10m-resolution) acquired between March and August 2015, phenological parameters were estimated using a function fitting approach. We then compared results with phenology retrieved from four years of 30 m Landsat 8 OLI data, and single-year 100 m Proba-V and 250 m MODIS temporal composites of the same period. Retrieved phenological parameters from combined RapidEye/SPOT5 displayed spatially consistent results and a large spatial variability, providing complementary information to existing vegetation community maps. Retrievals that combined four years of Landsat observations into a single synthetic year were affected by the inclusion of years with warmer spring temperatures, whereas adjustment of the average phenology to 2015 observations was only feasible for a few pixels due to cloud cover around phenological transition dates. The Proba-V and MODIS phenology retrievals scaled poorly relative to their high-resolution equivalents, indicating that medium-resolution phenology retrievals need to be interpreted with care, particularly in landscapes with fine-scale land cover variability.

Broedsucces van kustbroedvogels in de Waddenzee : Resultaten 2015-2016 en trends in broedsucces in 2005-2016

Data have been collected on the breeding success of several characteristic coastal breeding birds in the Wadden Sea each year since 2005. Ten birds species considered representative of specific habitats and food groups are being monitored. The monitoring scheme on breeding success in coastal breeding birds is run as an ‘early warning system’ to follow the reproductive capacity of the bird populations in the Wadden Sea and understand the processes underlying fluctuations in populations. It is a valuable addition to the monitoring of population numbers and is carried out under a trilateral agreement with Germany and Denmark (TMAP). The results from 2015–2016 and an analysis of data series from the period 2005–2016 (sometimes longer) show that several species on average reared too few young to sustain stable population size in many of these years, especially the Eurasian Oystercatcher, Pied Avocet, Common Tern and Arctic Tern, and in recent years also the Black-headed Gull, whose breeding success has significantly declined since 1995. Other species showing a significant decline in breeding success are the Spoonbill and Common Tern. The only species to show any significant improvement in breeding success since 2005 is the Lesser Black-backed Gull