Seeing me in the window, the tit pair flew away. The bat did not look well, but we decided to gently flip it over with a stick and let nature take its course. The parti-colored bat recovered for 10 minutes and then flew off. Fingers crossed she finds a safer roost this time!

Today I heard a pair of great tits just outside my office window, followed by a loud thump of something against the windowsill. I rolled up my blinds and to my surprise, there was a bat! This tit had knocked a bat from her roost and looked like he was thinking about lunch…

A pair of blue tits begging for food on their first morning outside of their nestbox. Hopefully I will see them again next year!

Size differences between male and female cowbird chicks may be more important in host nests where host chicks are a similar size. More research is needed in this area to answer these further questions.

We think it’s because even the smallest female cowbird was still much larger than the largest warbler chick, so it may be the size hierarchy and not the exact size difference that is the most important in this system.

However, when comparing nests parasitized with a male vs female cowbird, we found no differences in warbler size, fledging age, or survival! We know that parasitism by cowbirds negatively affects all of these things compared to nonparasitized nests, so why no difference?

This is really important because it could affect host demography, if male cowbird eggs are more likely to be laid during specific times of the year or in the nests of hosts of a certain quality, as female birds are able to bias the sex of the eggs they lay!

Male cowbirds are larger than females, and this is apparent even as chicks - males weigh significantly more than females. We hypothesized that larger, male cowbirds would cause warbler host nestmates to be smaller, fledge later, and have higher mortality because of the heightened competition.

Brood parasitic brown-headed cowbirds lay their eggs into the nests of prothonotary warblers. The cowbirds are much bigger than their warbler siblings, and outcompete them for food from their parents.

We are recruiting students interested in a thesis/internship in behavioral ecology to work with us this field season (Apr-July 2025) on breeding great & blue tits. We don't have internal funding, but we are happy to help students within the EU apply for Erasmus+ projects. erasmus-plus.ec.europa.eu