Caught on camera: identity crisis for blue tit chicks after being raised by the wrong parents

Wildlife cameras in nest boxes often reveal a fascinating glimpse into the private world of birds.

But one such camera at The Lodge Forest Visitor Centre in Aberfoyle uncovered a truly remarkable family situation this summer, as a pair of great tits were recorded raising both their own chicks, and two blue tit chicks at the same time.

The nest was first discovered in early June, and two of the eggs in the clutch were quickly identified as belonging to a different species. The eggs all hatched together, but despite being dwarfed by the much larger great tits, the two blue tit chicks fought their way to the front at feeding time, and managed to not only survive, but thrive, fledging at the same time as their adopted siblings.

This behavior is not unknown amongst blue tits and great tits, but it is rare to catch it on film.

Territorial arguments for good nesting sites are thought to lead to the larger great tits displacing their smaller rivals, sometimes after they’ve already laid their eggs. But blue tits have also been recorded sneaking back in after the takeover and adding a few eggs of their own, perhaps as a last ditch breeding strategy.

Ami Kirkbright, RSPB Scotland Wildlife Information Officer, said: “Watching this little great tit nest with a mixed brood of chicks has just been incredible. It’s something that no one here has ever seen before, it was really fascinating to research what was happening, and then follow their progress over the weeks.

“We get some really privileged views of wildlife on our cameras here at The Lodge, with birds like our ospreys and owls, as well as lots of other animals, including pine martens and red squirrels. But these little great tits and blue tits have been the star of the summer I think, not only for me, but for many of the visitors coming into the centre.”

Scientists studying the long-term repercussions of these shared nests have discovered that the fostered blue tits fledge believing that they are great tits and start their adult life using incorrect songs and calls, before eventually reverting back to 'proper' blue tits.

For birds which may only have one breeding attempt in their short lives, this may imply that the furtive egg laying strategy is an evolutionary tactic for the blue tits: a last resort which allows them to pass on their genes even after they’ve lost their nest.

It’s probably much less common for great tit chicks to be raised by blue tits, though this did occur in one of the BBC Springwatch nest boxes in 2016. When this happens, it is probably accidental rather than a breeding strategy, as the great tit chicks seem to be stuck thinking they’re blue tits for their entire lives, and are never able to mate successfully.

The Lodge Forest Visitor Centre is managed by Forest Enterprise Scotland and the wildlife viewing project is a partnership between RSPB Scotland and Forest Enterprise Scotland.