Experimental evidence for cryptic interference among socially foraging shorebirds

Foraging rate and the distribution of foragers depend on prey distribution in conjunction with interindividual interactions. Generalized functional response models predict intake rates and spatial distributions of foragers on the basis of resource distribution and interference competition. The adequacy of these models depends on how well they capture the foragers’ essential behavior. In this paper, we report on the results of a foraging experiment designed to examine the mechanisms of interference competition using red knots Calidris canutus that feed on buried bivalves. Red knots are rarely observed to interfere in the field, but this does not imply absence of interference. Our experimental setup minimized resource depletion, which allowed us to quantify interference competition as the decline in intake rate as a function of group size, with prey density and social status as additional treatments. We found that intake rate and searching efficiency decreased with group size and that dominant birds had higher intake rates than subordinates. Additionally, time spent searching for prey increased with group size. The decrease in intake rate was not due to conventional interference mechanisms (such as kleptoparasitism and time spent interacting with conspecifics) but to ‘‘cryptic interference,’’ that is, avoidance of physical encounters with conspecifics. To accurately predict intake rates and foraging distributions, theory and models need to account for the possibility that animals anticipate and try to avoid, at some costs, physical encounters with conspecifics (i.e., conflicts that would make conventional interference behavior visible).

A mud budget of the Wadden Sea and its implications for sediment management

The world’s coasts and deltas are progressively threatened by climate change and human activities. The degree at which coastlines can adapt to these changes strongly depends on the sediment availability. The availability of muddy sediments is however poorly known. This study aims at developing a mud budget for the world’s largest system of uninterrupted tidal flats: the Wadden Sea. The resulting mud budget is nearly closed: ~ 12 million ton/year enters the system on its western end, ~ 1.5 million ton/year is added by local rivers, while ~ 12 million ton annually deposits or is extracted by anthropogenic activities. A mud deficit already exists in the downdrift areas, which will only become more pronounced with increased sea level rise rates. Mud is thus a finite resource similar to sand, and should be treated as such in sediment management strategies. Resolving future challenges will therefore require a cross-border perspective on sediment management.</p

Additional file 13 of WATLAS: high-throughput and real-time tracking of many small birds in the Dutch Wadden Sea

Additional file 13. Data file with localizations to calculate home ranges for sanderling as shown in Fig. 9A. TAG represents Individual tag identity, TIME is UNIX time (s), X is the X-coordinate of localizations (m, UTM 31N), Y is the Y-coordinate of localizations (m, UTM 31N), NBS is the number of base stations used to calculate localizations, VARX is the Variance in X coordinates, VARY is the Variance in Y coordinates, COVXY is the Covariance between X and Y coordinates, ts is the timestamp (CET), tideID is the tidal cycle identity, tidaltime is the time past high tide (minutes), and waterlevel is the waterlevel at west-terschelling (cm)