Mixed Species Tit Flocks

 It is at this time of year when the leaves are falling from the trees and the birds start to flock together that mobile tit flocks are more evident.

Back in university, my dissertation looked at optimal foraging theory in woodland birds and it was at this time that I first noticed the phenomena known as mixed species flocking. I made my study in Penglais Wood, just over the road from the main campus of Aberystwyth University. I walked this woodland several times a week counting the birds and trying to time foraging events. 

The busiest spot was always in a clearing of beech trees. Beech trees are amazing organisms, their thick foliage means that very little ground cover grows beneath them and in winter their golden leaves drop to form a thick carpet that becomes full of small insects and beech masts. This feast attracted the likes of Blackbirds, Thrushes, and Redwings but also flocks of smaller birds. Chaffinches were predominant alongside Great Tits, with Blue Tits, Wrens, and Treecreepers flitting in the branches. Watching these flocks led me into reading up on Hurlbert's work on Niche Overlap theory, a post for another time perhaps.

Today I see these flocks regularly on my patch. The core of these flocks tends to be the ever-gregarious Long-tailed Tit family groups. They assemble post-breeding in extended families and can number into the mid-teens. With them, travel Blue Tits and Great Tits with very occasionally a Coal Tit or Marsh Tit. What makes these little flocks more interesting are the added extras who come along for the ride. Mixed in amongst the flurry of little bodies is often a Treecreeper or two or Goldcrest, rarer still are Nuthatch or overwintering Blackcap.

Mixed species Tit flocks are not hard to miss. They are noisy and fill the air with a cacophony of cherubic tweets and frantic dashes between trees. The woodland or hedgerow suddenly comes alive with little bodies flitting hither and thither. It can be somewhat overwhelming having so many birds whizzing about, flocks can sometimes reach upward of twenty individuals or more. Counting such events can be difficult but I find the easiest way is to position oneself in a gap between two trees and then try and count them as they fly between them.

Small passerines find such flocks very advantageous. In the autumn and winter without the leaf cover, such small birds are terribly exposed to predators such as the Sparrowhawk, by traveling en masse they increase the number of eyes looking out for harm and can alert the whole group to danger with high-pitched frantic alarm calls. Large numbers also confuse the Sparrowhawk by providing too many targets for it to choose from. They are able to continue to forage in this way moving from tree to tree and exhibit great niche seperation. The long-tailed tits and goldcrests feed on the slender branch tips, Blue Tits and Great Tits on the larger branches, and the Treecreepers on the trunk.

In my experience, the bosses of this flock are the Long-tailed Tits. I have never seen a mixed species tit flock that did not include 'Longties', they take the lead and the others follow. Such flocks can turn a quiet still woodland walk into a bonanza of sound and movement, another one of natures little miracles.