By Rike Bolam
Dippers are the only songbirds that can swim and feed underwater. The river Derwent offers great habitat for these small but strong birds as it is not polluted and has therefore plenty of food on offer. It also provides lots of natural nest sites for dippers to build their nests and raise broods. Maybe this is why it has one of the highest densities of dippers in the country! We monitor dipper pairs between Swalwell and Ebchester.
We first started monitoring dipper nests in 2012. The adults build nests with moss in bridges or on cliffs along the river, or even under waterfalls! The nests are usually above running water and when the young birds fledge they can swim straight away. We record the various stages of nest building and egg laying and also ring the young birds in the nest. That way we can monitor in the following years where the birds move and how long they live. We can also estimate if the productivity in a particular year was good or bad. For example, if it is cold until late spring, there may be fewer nests, and the birds may also lay fewer eggs.
Monitoring adult dippers
We also catch some adults near their nest sites, to monitor their movements between years and to collect data that can be used to estimate how long dippers live for. Sometimes we also recapture birds that were ringed as nestlings. Females are smaller than males, so we can generally tell which is which. Based on how many generations of feathers we see, we may also be able to tell how old a bird is.