Claudia Schüz


4277 57402

PDF der Diplomarbeit im Hochschulschriften-Service der Universität Wien

Vigilance and feeding behaviour of Ruffs Philomachus pugnax during spring migration in Eastern Austria.

This study tested for effects of flock size and other potentially important variables (location, vegetation cover, wind force, cloud cover, date, time and feeding habitat) on vigilance level and food intake of foraging Ruffs Philomachus pugnax during spring migration at Seewinkel, an important stopover site for waders in Eastern Austria. Therefore, foraging Ruffs were filmed at four different salt ponds. Finally, a total of 681 film sequences were available for analysis. The two main components of foraging behaviour, vigilance and food intake, measured as scan rate (number of scans per 30 sec) and peck rate (number of pecks per 30 sec), respectively, were not correlated. To test for effects of predictor variables on scan and peck rate of foraging Ruffs Generalized Linear Models (GLMs) were calculated including all variables and all possible subsets. Three variables remained in the 12 best GLMs (selected according to Akaike´s Information Criterion) testing for effects on scan rate of foraging Ruffs: feeding location, feeding habitat and flock size. These variables also significantly affected Ruffs´ scan rates according to Wald statistics. Besides differences of scan rates between feeding locations, vigilance level was significantly higher in terrestrially foraging Ruffs than in birds feeding at semi-aquatic habitat patches. Furthermore, scan rate decreased with increasing flock size. To test for effects of the eight aforementioned predictor variables on peck rate, the mobility of Ruffs during foraging quantified as number of steps per 30 sec was included in all calculated GLMs. Four of the nine predictor variables remained in the best model: location, wind force, cloud cover and date. Two of them, feeding location and wind force, were included in all 23 best models and had a strong effect on peck rate according to Wald statistics. Peck rate increased with increasing wind force. GLMs to assess effects of moult stage and colour morph of males (indicating their social status) on vigilance and peck rate additionally only included predictor variables, 2 which already proved to have a significant effect on scan and/or peck rate (location, feeding habitat, flock size, cloud cover and wind force). Furthermore, we included the date as predictor variable and allowed for a two-way interaction between date and moult stage and male plumage colour, respectively, because both the proportion of birds with different moult stage and birds belonging to different colour morphs changed with progressing spring migration. Calculated GLMs did not indicate any significant effects of moult stage or social status of males on scan and peck rate. Our study emphasized that even when controlled for other variables affecting scan rates, flock size still remains important for explaining variance in vigilance levels of foraging Ruffs. In contradiction, flocking did not directly affect food intake rate. However, stepping rate of birds decreased with increasing flock size indicating a better access to prey at sites where larger flocks aggregate. This is confirmed by the observation that food intake indeed increased with declining stepping rate. Furthermore, our observation that Ruffs´ vigilance and food intake significantly differed between salt pans has important implications for conservation.

Gewinner des Nationalpark-Preises 2013

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