Great tits are killing birds and eating their brains. Climate change may be to blame.

https://www.popsci.com/great-tits-murder-climate-change?cmpid=ene20190112&utm_source=internal&utm_medium=email&cid=46539&mid=401399543


Every year, little black-and-white birds called pied flycatchers make the lengthy trek from sub-saharan Africa to northern Europe to feast on caterpillars, claim a nest, and have babies. This typically goes off without a hitch, and the birds return to Africa a few months later, offspring in tow. But recently, some flycatchers have arrived to find their nesting sites occupied by haughty, territorial great tits. And those birds don’t just chase flycatchers away—they brutally attack them, kill them, and eat their brains.
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The reason for such grisly bird murders might be due to a shift in migration and nesting timelines for both birds, according to a new study published Thursday in Current Biology. While great tits typically breed two weeks earlier than pied flycatchers, their breeding periods now occasionally overlap due to climate change-related factors, the authors say.

Great tits live in European forests like the Dwingelderveld and Drents Friese Wold forests in the Netherlands, where the study took place, all year round. Flycatchers, on the other hand, are merely regular vacationers. Since the 1980s, flycatcher breeding season has been inching up earlier in the month of April. Warm spring temperatures have caused caterpillar populations to boom sooner in the month, so flycatchers adapted to that and started arriving a bit earlier, too. That wouldn’t be too big a problem for flycatchers, except that great tit breeding periods are also in flux. Now, when tits delay their breeding period a little bit in colder Aprils, they overlap with the flycatchers, and violence ensues.