During copulation, males of Bombus terrestris fill the queen's sexual tract with a mating plug after transferring their sperm. The sticky secretion is produced by the male's accessory glands and disappears within a couple of days. Experiments now show that the primary function of the plug is to reduce the subsequent mating probability of the queen. The plug is not efficient in preventing sperm migration into the spermatheca. Due to its low energetic value, the plug is also unlikely to serve as a nuptial gift. This type of male interference with female mating propensity has so far not been found in social insects. This finding could, at least tentatively, explain why females of B. terrestris may not be able to take advantage of the demonstrated benefits of multiple mating. Furthermore, such male interference could be a more general phenomenon in social insects, with obvious ramifications for the evolution of polyandry in this group.
Other than during periods of migration, animal movement tends to be poorly described, despite the potential importance of such movements, which may prove crucial for surviving periods of bad weather and low food availability. We analysed within‐winter (December–February) movements of Mallard using the EURING Data Bank. Most movements were directed towards the south or southwest during all three winter months. Distances covered increased with winter harshness and generally decreased from 1952 to 2004. Mallards appear to move less than other duck species during winter. Long‐distance movements of Mallards seem to be related to cold weather, birds only moving long distances in large numbers during the very coldest winters. Movements are not restricted during midwinter, but occur throughout the winter. The decreasing within‐winter movement over time (1952–2004) could be explained by decreasing reporting probabilities and/or warmer winters in recent decades. However, the first is only true if the decrease in reporting probability increases with distance moved, for which we found no indication in our study. Therefore, we suggest that the pattern found is evidence of long‐term winter warming reducing the distance of within‐winter movements in this species.
Ring re‐encounter data, in particular ring recoveries, have made a large contribution to our understanding of bird movements. However, almost every study based on ring re‐encounter data has struggled with the bias caused by unequal observer distribution. Re‐encounter probabilities are strongly heterogeneous in space and over time. If this heterogeneity can be measured or at least controlled for, the enormous number of ring re‐encounter data collected can be used effectively to answer many questions. Here, we review four different approaches to account for heterogeneity in observer distribution in spatial analyses of ring re‐encounter data. The first approach is to measure re‐encounter probability directly. We suggest that variation in ring re‐encounter probability could be estimated by combining data whose re‐encounter probabilities are close to one (radio or satellite telemetry) with data whose re‐encounter probabilities are low (ring re‐encounter data). The second approach is to measure the spatial variation in re‐encounter probabilities using environmental covariates. It should be possible to identify powerful predictors for ring re‐encounter probabilities. A third approach consists of the comparison of the actual observations with all possible observations using randomization techniques. We encourage combining such randomisations with ring re‐encounter models that we discuss as a fourth approach. Ring re‐encounter models are based on the comparison of groups with equal re‐encounter probabilities. Together these four approaches could improve our understanding of bird movements considerably. We discuss their advantages and limitations and give directions for future research.
Common and widespread species often show a large variability in behaviour and habitat use. Such variability at the species level may result from individuals themselves being very variable or, alternatively, variability may arise from differences between individuals. The aim of this study was to explore land use in general and betweensubject variability in the local movements and daily activity patterns of Mallards Anas platyrhynchos in central Switzerland during the winter. The Mallard is a common duck species and can be found on almost all types of water bodies. We equipped 24 ducks with VHF radio tags and searched for these ducks 1-3 times per day. We also used nine tags that automatically recorded their location every 30 min as well as acceleration in three dimensions every 2-5 min. These methods yielded information on the activity of the duck with a high temporal resolution both day and night. The 24 ducks were strongly linked to water, and 97% of all localisations were within 50 m of a water body. An affinity to settlements was only observed in the vicinity of the main lake in the area, but not for those ducks on smaller water bodies or fields. Some individuals were very stationary, using only a small area during the study period; others made daily commuting flights between two sites about 8 km apart while still others moved around similar distances but in varying directions. Rain and increasing wind speed correlated with decreasing movement activity. However, the effect of these weather parameters, and especially that of temperature, varied between individuals. Activity was strongly influenced by the sun's movement, with general activity and flight activity being highest around sunrise and sunset. This daily pattern was similar for all individuals. Hence, while the activity pattern was similar for all individuals, the resulting degree of local movements and the response to changing weather parameters were very variable among individuals. Keywords Mallard Á Anas platyrhynchos Á Winter Á Land use Á Daily activity pattern Zusammenfassung Individuelle Variabilität im Verhalten eines ökologischen Generalisten: Aktivitätsmuster und lokale Ortswechsel bei der Stockente (Anas platyrhynchos) im Winter Häufige und weit verbreitete Arten zeigen oft eine große Variabilität in Verhalten und Habitatnutzung. Diese Variabilität auf Artniveau kann sowohl durch ein vielfältiges Verhaltensrepertoir eines jeden Individuums entstehen, als auch durch große Unterschiede zwischen den Individuen. In dieser Studie untersuchten wir, wie Stockenten Anas Communicated by F. Bairlein.
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