Posted | filed under Weekly Banding Reports.

The LSLBO has finished our second round of MAPS banding focusing on our breeding birds. With 61 birds banded in the last period, our MAPS banding total now stands at 173 birds banded from 21 species. Although there were no captures that stood out in the last round, we are expecting this round to be full of baby birds that have left the nest, but are not quite independent of their parents who are faithfully following them and caring for them. With these baby birds will also come Hippoboscidae – a parasite more commonly known to banders as flat flies!

These parasites feed on the blood of birds and mammals and tend to be highly specialized to their hosts. Relatively little is known about this group since they are rarely collected. In order to fit nicely between a bird’s feathers, these flies look as though you took a normal house fly and squished it in a book. Although they are very good at eliciting reactions of disgust, they (thankfully) do not bite humans and rarely do they severely harm their avian hosts.

Above: This flat fly under 2x magnification was collected off one of our songbirds this spring. Although it is roughly 7 mm long, it is only approximately 1 mm high.

Alongside our banding projects this year, we are sampling flat flies from captured birds in our second year of a collaborative project coordinated by researchers at the University of Guelph.  This Canada-wide project will provide a survey of flat fly diversity, their associated avian host species, and seasonal trends in their abundances. It is already suggested that there are over 200 species of Hippoboscidae, of which 75% of species parasitize birds. Moreover, researchers hope to study the mites that parasitize the parasitic flat flies and potentially describe new species.

At least 281 flat flies were collected by the LSLBO in 2021, but so far this year we have collected just 3. We are not yet concerned about this small sample since a similar trend was discovered last year when no flat flies could be found throughout the spring until the fledglings began moving around carrying these tiny passengers. Interestingly, even on adult birds, the females were far more likely to have flat flies than the males. For the flat flies, it does make sense that they would be most abundant and mobile when young birds are present since these chicks may be their only chance to find new songbird hosts.

This seasonality has us wondering where these parasites come from in the first place: Do they spend the spring migration in a nymphal stage we are not recognizing? Are they somehow spending the winter in old nests? Do their squashed bodies make them too good at hiding until they actively begin looking for new hosts? Although someone may already have the answers to these questions, a brief adventure through the literature has not turned up any results. We are eager to see what other mysteries these collection efforts may reveal (and hopefully solve).

By Robyn Perkins, LSLBO Bander-in-Charge