New research has highlighted how biting insects can directly affect the nesting success of Great Northern Divers.
When sitting on a nest to incubate eggs, a bird is physically stuck and at its most vulnerable to attacks of any kind, so coping with stress and other significant costs is important. For Great Northern Divers, black flies are a common blood-feeding pest and can cause nest abandonment and decreased fledging rates. This has impacts on not only individual pair success, but on population dynamics as well.
The new study has presented some of the best data to date to support hypotheses about the effects that black flies have on diver nesting behaviour and success. Chapman University’s Walter Piper and his colleagues monitored Great Northern Diver nests for 25 years in northern Wisconsin, USA. They marked individuals to track each bird’s behaviour, nesting success and interaction with black flies. More than 2,050 nests were included in the study to assess the impacts of black flies on divers at population level.
If the black fly concentration around an individual bird was high or it was a particularly intense fly outbreak year, diver incubation time decreased and nest abandonment increased. It was discovered that nest abandonment could be predicted using lake size, female age and the amount of wind. The team found that the smaller the lake, the older the female and the greater the distance across water that wind has to travel to reach the nest, the more likely it is that the nest will be abandoned.Read on