Daily and Seasonal Activity of Moorhens Studied by Motion-Sensitive Transmitters

Abstract

-We studied the diurnal and seasonal activity budget of Moorhens (Gallinula chloropus) along a river in NW Italy. Since visual observations are sometimes difficult, we utilized radio-tracking with motion-sensitive transmitters, a technique that distinguishes between resting and walking/foraging activities. Radio-tracking estimates of the home ranges provided values (mean 3-5 ha) about one order of magnitude higher than those reported in the literature and based on visual estimates. Analysis of habitat preferences showed a positive selection for reeds, marsh woods and stretches of water, while cultivated fields were avoided. The percentage of time spent in activity during the day was distributed differently between the colder (December to February) and warmer months (March and April). In winter, the birds were active mainly in the early morning, and resting increased progressively as the day proceeded. In spring, activity was distributed uniformly throughout the day. However, there was no overall difference between the colder and warmer periods in the total time spent in activity each day (about 44%). The time spent in activity was not related to daily temperature. In the same group of birds, the fat reserves were progressively depleted during winter, as demonstrated by a gradual decrease of total body mass and fat; moreover, the loss of mass was greater on colder days. The findings for both activity budget and mass variation suggest that the birds do not try to counteract fat loss; they do not increase the time spent feeding in the colder months nor do they increase their activity during days with lower temperatures. Received I June 1999, accepted 22 October 2000.