Saturday, December 6, 2008

Blue Tit Parus caeruleus

I am an amateur naturalist trying to learn something about everything living in my garden.

Some of you may recall that in my posting on White Tipped Bristle Moss I mentioned being impressed at the performance of the camera I was fortunate enough to borrow on that occasion. Well, I'm pleased to announce that the birthday fairies have since visited and I am now the proud owner of a fancy digital SLR. I offer this in explanation for why I have spent the greater part of Saturday morning, crouched in a 'birdhide' (a.k.a my garden shed!) my zoom lens trained on my garden birdfeeder.

Blue Tits (Parus caeruleus) are small birds (around 11gm, 11cm), easily recognised by the yellow breast, black eye stripe on a white face, blue crown, and blue and green dorsal (=viewed from back) feathers (photo 2 - click to enlarge). With experience (which I don't have!) it's apparently possible to distinguish males from females by the slightly smaller size and less vivid colourings of the latter.

The Blue Tit's call is a high pitched 'tsee-tsee-tsee' or occasionally a scolding 'churr'. They are one of Britain's commenest birds: The RSPB website gives the number of breeding pairs in the UK as approximately 3.5million.

According to my copy of The Blue Tit (Jim Flegg, Shire Natural History) female Blue Tits normally lay a single batch of between 5- and 16-eggs, during March or April. As with Robins, life is hard, and annual mortality in Blue Tits is around 90%. I had not hitherto realised that predators of the chicks include the Greater Spotted Woodpecker. Late summer and autumn see the highest mortality rates. More happily for my blue tit, birds that make it into Winter have a decent chance of reaching the Spring.

During Spring male Blue Tits defend terretories. During Autumn these break down and Blue Tits join large flocks of small birds roaming the hedgerows. During Winter a sort of 'half way house' emerges with birds forming smaller flocks and confining their travels to smaller (300-400m^2) areas. Again, like Robins, UK Blue Tits tend not to travel any great distance during their lives, <1% moving more than 100km although every few decades climate conditions lead to mass influxes ('irruptions') of birds from the European mainland.

A puzzle about Blue Tits, described in the book above, relates to their dietary fondness for Winter Moth (Operohtera brumata) and Tortix caterpillers. In some years in Oak woodlands, these attain epidemic proportions. Blue Tits seem able to predict (or to state things less anthopromorphically - there is a correlation between) when, and how many eggs to lay to take best advantage of the arrival of the caterpillers. How they do this isn't known, or at least wasn't when the book was written.

Finally, a fact well know to Brit's of a certain generation, which I include here for the interest of overseas readers, was the tradition (now rendered largely extinct by the ubiquitous supermarket) of having milk delivered to the doorstep in glass bottles capped with aluminium foil. It was to a national hazard to find Blue Tits had pecked through the foil to get at the cream below. You can find a photo of this here. Charming at first, but the householder soon learnt to leave empty youghurt pots out for the milkman to place over the bottles to thwart the theives!

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