Kees Camphuysen

Migration pattern of Icelandic Lesser Black-backed Gulls Larus fuscus graellsii: indications of a leap-frog system

AbstractOn the species level, the non-breeding distribution and the migration patterns of most European birds are well known. In contrast, the knowledge of the contribution of different breeding populations to particular non-breeding sites (migratory connectivity) is far more limited. We studied the non-breeding distribution of individually colour-ringed Lesser Black-backed Gulls (Larus fuscus graellsii) from Iceland and sought information on their migration pattern in respect to other populations (leap-frog, chain migration, random mix). Most winter resightings (94%) were from the southern part of the known winter range (Iberian Peninsula and northwest Africa). No statistical difference was found according to age on the latitudinal winter distribution, although 1st winter birds were on average 2° further south. Both 2nd and 3rd calendar year (cy) birds performed a northward spring migration,but spent the summer at lower latitudes than adults. The autumn migration for adults was earlier compared with 1st cy birds. A comparison of resightings of birds ringed in Iceland and in two projects from the Netherlands showed that these populations are not likely to contribute much to the wintering population in the UK. The proportion of winter resightings from Icelandic and Dutch populations showed that 44–65% were from the Iberian Peninsula. However, Dutch birds were much more likely to be seen in France (18–48 vs. 0.4%), but Icelandic birds were more likely to be seen in Africa (29 vs. 6–16%). These results indicate that Icelandic birds to some extent leap-frog more southerly populations.ZusammenfassungZugmuster der Isländischen Heringsmöwe (Larus fuscus graellsii): Hinweise auf ein Übersprungs-System Auf Art-Niveau sind das Vorkommen und die Zugmuster der meisten europäischen Vögel gut bekannt. Deutlich weniger weiß man hingegen über die Präsenz der unterschiedlichen Brut-Populationen in Gebieten, in denen nicht gebrütet wird (migratory connectivity). Wir untersuchten das Vorkommen einzelner beringter, isländischer Heringsmöwen (Larus fuscus graellsii), um Informationen über ihre Zugmuster in Zusammenhang mit anderen Populationen zu sammeln (Überspringen, Kettenwanderung, Zufalls-Mix). Die meisten (94%) Ringfunde und Sichtungen lagen im südlichen Teil der bekannten Überwinterungsgebiete (Iberische Halbinsel, Nordwest-Afrika), und es gab keine statistischen Unterschiede bezüglich des Alters der geographischen Winter-Verteilung, obwohl erstmals überwinternde Vögel im Schnitt 2 Grad weiter südlich zu finden waren. Vögel, die zum zweiten und dritten Mal überwinterten, zeigten eine mehr nördlich ausgerichtete Frühlingswanderung, verbrachten den Sommer aber auf südlicheren Breiten als die adulten Tiere. Die Herbstwanderung adulter Tiere ist früher schon mit der von Erstziehern verglichen worden. Ein Vergleich von in Island beringten Wiederfunden wie auch zwei Projekte in den Niederlanden zeigten, dass diese Populationen höchstwahrscheinlich nicht viel zu den im U.K. überwinternden Populationen beitragen. Ein Teil der Winter-Wiederfunde isländischer und niederländischer Populationen zeigte, dass 44–65% von diesen von der Iberischen Halbinsel stammten. Aber niederländische Vögel wurden mit größerer Wahrscheinlichkeit in Frankreich gesichtet (14–48 vs. 0.4%) und isländische Vögel eher in Afrika (29 vs. 6–16%). Diese Ergebnisse sind ein Hinweis darauf, dass isländische Vögel in gewissem Ausmaß südlichere Populationen überspringen.

The most common diet results in low reproduction in a generalist seabird

Abstract Dietary specialization has been described across a wide range of taxa in the animal kingdom. Fitness consequences are, however, not well documented. We examined the reproductive consequences of different dietary specializations in the herring gull Larus argentatus, an omnivorous seabird, using an extensive dataset which includes breeding and dietary data of 10 successive years. We hypothesized that pairs that focused on prey of higher energetic value would yield higher fledging rates. An alternative hypothesis is that pairs that relied on more resources simultaneously would reproduce better. The novelty of this study is that we used continuous measurements representing dietary composition and degree of specialization rather than restricting our analysis to predefined categories. By relating these two continuous measurements for diet to several proxies for reproductive success, we show clear consequences of dietary choice. Most pairs concentrated on bivalves, a prey type not particularly rich in energy. Pairs feeding on energy‐rich prey (e.g., “domestic refuse and fishery discards”) during chick rearing were found to have a higher reproductive success, supporting the first hypothesis. Pairs that used more resources did not clearly have a higher reproductive success. The majority of the pairs did not switch to energy‐rich prey during chick rearing, despite low breeding outcome. We discuss how trade‐offs between factors such as resource availability, predictability, and the time and energy needed to obtain certain prey species may influence resource selection.

Global phenological insensitivity to shifting ocean temperatures among seabirds

Reproductive timing in many taxa plays a key role in determining breeding productivity1, and is often sensitive to climatic conditions2. Current climate change may alter the timing of breeding at different rates across trophic levels, potentially resulting in temporal mismatch between the resource requirements of predators and their prey3. This is of particular concern for higher-trophic-level organisms, whose longer generation times confer a lower rate of evolutionary rescue than primary producers or consumers4. However, the disconnection between studies of ecological change in marine systems makes it difficult to detect general changes in the timing of reproduction5. Here, we use a comprehensive meta-analysis of 209 phenological time series from 145 breeding populations to show that, on average, seabird populations worldwide have not adjusted their breeding seasons over time (−0.020 days yr−1) or in response to sea surface temperature (SST) (−0.272 days °C−1) between 1952 and 2015. However, marked between-year variation in timing observed in resident species and some Pelecaniformes and Suliformes (cormorants, gannets and boobies) may imply that timing, in some cases, is affected by unmeasured environmental conditions. This limited temperature-mediated plasticity of reproductive timing in seabirds potentially makes these top predators highly vulnerable to future mismatch with lower-trophic-level resources2.Time of reproduction may be altered as the climate changes. For seabirds, it is shown that there has not been an adjustment in timing as the climate changes and the sea surface warms. This lack of plasticity could result in a mismatch with food resources.

Estimating the spatial position of marine mammals based on digital camera recordings

Estimating the spatial position of organisms is essential to quantify interactions between the organism and the characteristics of its surroundings, for example, predator–prey interactions, habitat selection, and social associations. Because marine mammals spend most of their time under water and may appear at the surface only briefly, determining their exact geographic location can be challenging. Here, we developed a photogrammetric method to accurately estimate the spatial position of marine mammals or birds at the sea surface. Digital recordings containing landscape features with known geographic coordinates can be used to estimate the distance and bearing of each sighting relative to the observation point. The method can correct for frame rotation, estimates pixel size based on the reference points, and can be applied to scenarios with and without a visible horizon. A set of R functions was written to process the images and obtain accurate geographic coordinates for each sighting. The method is applied to estimate the spatiotemporal fine-scale distribution of harbour porpoises in a tidal inlet. Video recordings of harbour porpoises were made from land, using a standard digital single-lens reflex (DSLR) camera, positioned at a height of 9.59 m above mean sea level. Porpoises were detected up to a distance of ∽3136 m (mean 596 m), with a mean location error of 12 m. The method presented here allows for multiple detections of different individuals within a single video frame and for tracking movements of individuals based on repeated sightings. In comparison with traditional methods, this method only requires a digital camera to provide accurate location estimates. It especially has great potential in regions with ample data on local (a)biotic conditions, to help resolve functional mechanisms underlying habitat selection and other behaviors in marine mammals in coastal areas.