Gedrag van pleisterende Regenwulpen Numenius phaeopus in Noord-Drenthe

The behaviour of temporarily staying Whimbrels in spring in the northern Netherlands (Fig. 1) was described by scoring the behaviour of flocks (n=157) and solitary birds (n=26 birds, during a total of 145 minutes) in grassland. Fig. 2 shows the types of behaviour as recorded during this study. Behaviour of Whimbrels in flocks or solitary did not differ from one another, and were therefore grouped. Birds spent most of their time walking, looking, pecking and probing. Although pecking showed a high frequency of occurrence per minute (32%), it took only 18% of the time (Table 1). Walking and looking accounted for almost 50% of the time spent on the foraging grounds (Table 1). Throughout the day, pecking frequency seemed to decrease slightly, but this was compensated by a higher frequency of probing (Fig. 3). Despite pecking being an important activity, it was rarely successful (3.7% of pecks was followed by swallowing), which compares unfavourably with probing (26.1% successful). The sequences of behaviour, and their interrelationships, are depicted in an ethogram (Fig. 4). Birds were frequently disturbed, resulting in vigilant behaviour or taking wing. Most disturbances were human-caused (62%), only 18% was thought to have had natural causes. Frequent disturbances may have a negative impact on food intake of Whimbrels prior to their flight to the breeding grounds. Similarly, intensification of agriculture has led to drainage of grasslands, which inhibits probe-foraging by Whimbrels. Although Whimbrels are quite versatile in their foraging strategy, drainage may also hamper successful foraging. In this respect, the decline in number of staying Whimbrels in spring in the province of Drenthe -an important foraging site in spring in the 1970s, with many important roosts- is significant.