Hi everyone, lets get into it.  The bird this week is the Eurasian blackcap, a common and widespread kind of warbler.  It lives in large chunks of Europe as well as Africa, and some of these birds will migrate within their range depending on local conditions.  Most interestingly, birds will migrate to different parts of the range based on where they were born.  Birds born to the west of around 10-11 degrees east longitude will migrate southwest toward west Africa or the Iberian peninsula.  Birds born to the east of this line will migrate to the eastern Mediterranean and east Africa.  Studies have shown that birds will follow this pattern regardless of where they actually live, the preference for where to migrate is based on genes, so a bird born on one side of the line but moved to the other will follow its heritage in planning a migration, rather than basing it on where it actually lives.  

This bird has made some interesting changes due to climate change.  More and more of them winter in Ireland and the UK.  Although this is not an ideal spot for them, climate-wise, it is advantageous because it allows for a shorter migration, avoiding the Sahara and the Alps, and because of the ready availability of food in bird feeders. Birds that winter near bird feeders are also shown to be healthier, have less stores of fat, rounder wings and a longer beak.  All of these changes reflect a more varied, generalist diet than birds which winter in more traditional spots further south.   Birds have been arriving in the northern end of their range sooner, two weeks earlier than they did in the 1980s.  They are also lighter and have longer wings than they used to, suggesting a longer migration route as their range extenders further northward.  

Blackcaps prefer mature deciduous forests with an established understory, which is a layer of vegetation below the trees but off the ground. This will include trees stunted by lack of sunlight as well as plants than can thrive in that environment, such as vines and shrubs.  Male blackcaps are territorial, and will defend their territory from other blackcaps and other birds that share their niche.  Nevertheless, in prime breeding areas in northern Europe, there may be as many as “100–200 pairs of birds per square kilometer (250–500 pairs per square mile), and 500–900 pairs per square kilometer (1,250–2,250 pairs per square mile) in Italy.”  No matter what measuring system we use, I think we can all agree that that is an assload of birds.  Blackcaps eat mostly insects during the breeding season, then switch to fruit in the late summer as compelled by their internal biological rhythm.  When eating fruit, the blackcap will squeeze out all of the seeds before eating the pulp.  This makes them an important distributor of the plants that they eat, particularly holly.  

Blackcaps sometimes fall victim to brood parasitism by cuckoos, but blackcap eggs look very unique and similar to each other in a single clutch, so the infiltration is not often successful.  Blackcaps are good at recognizing intruder eggs and will roll remove them from the nest if they are noticed.  Both members of a breeding pair will watch the nest, but on the the female broods overnight.  The selected nest is often built by the male as part of a courtship display, and consists of a small cup made of roots, stems and grasses that is often placed just a few feet off the ground.  Male blackcaps sport their eponymous black cap, the female has more of a rust colored cap.  There is a lot to learn about this bird, but these are some highlights.  Please feel free to check out my sources for more information.  Have a good weekend, everybody.

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