Tuesday, January 13, 2015

Blue Tit

This little angel will be familiar to most in the British Isles: a Eurasian blue tit or Cyanistes caeruleus. I was going to write Parus caeruleus, but the British Ornithologists Union treats Cyanistes as a separate genus, and not just a sub-genus of Parus. And rightly so, I hear you cry, because the mitochondrial DNA cytochrome B sequence in Cyanistes is completely different to that found in other tits found in Parus!

Well I'm glad we've cleared that little taxonomical peccadillo up.

I think I mentioned before that although they appear to lack sexual dimorphism, under ultraviolet light the males have brighter blue crowns.

They are the species most likely to set up home in your nest box (assuming it is one with an appropriate sized hole in the front and located in a suitable location) and if they do, and especially if you have one of those little cameras in the box so you can observe the goings-on, you'll find they temporarily become part of the family. It is extraordinary to see how hard the parents have to work to feed their chicks. Each chick needs around a hundred caterpillars every day. That often equates to parents returning every ninety seconds with another morsel. By the time fledging occurs the parents look proper knackered!

Last year we were lucky enough to catch the moment when the nippers fledged. A couple didn't make it to the bushes where mum and dad were waiting so we helped them get there before one of the local Felae cati turned up. (Actually how do you write binomials in the plural? I have tried to find out but so far without confident success.)

Blue tits made a bit of a media splash when they demonstrated cultutural transmission of learning to other tit species by 'passing on' the knowledge that if you pecked through the foil top of a milk bottle there was cream to be had. 

How does that work then? In evolutionary terms it can't be that the blue tits are giving the knowledge altruistically to their close relatives. It must be more that organisms are evolved to pick up clues and signals relating to food availability, in the same was as they are evolved to chose mates to maximise breeding success?

There are around 3.5 million breeding pairs according to the BTO. The average lifespan is only around 2 years but a lot don't survive beyond the first few weeks when they are most vulnerable to predation. The oldest recorded blue tit was more than eleven years old.

Now that I've discovered how to embed sound clips from xeno-canto (about which I was very excited and ever so slightly cocky) I feel duty bound to include them whenever appropriate.





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