Sunday, 31 October 2010

Doing a Packham

OK; so Chris Packham is younger and much more talented, but I felt a bit like him yesterday when I decided to count the number of black sunflower seeds in my large feeder.

You may justifiably ask why I would wish to do this. But first of all the result of my efforts. I counted the number of seeds in 1cm (roughly 110) and then multiplied by the length (65cm) to get an estimate of around 7100 to 7200.

I referred in previous posts to the three Coal Tits that have been feeding on this seed and also building up a cache. I have read that this caching activity is particularly prevelant in October and my feeder has certainly been emptied each week for the last month. The other major users of the black sunflower seed feeder are Greenfinches, Blue and Great Tits.

My last post referred to a new garden record of nine Greenfinches on the feeder at once. I had ten today. I have at least two pairs of Blue Tits and one pair of Great Tits visiting regularly. Greenfinches usually eat at the feeder and can husk and eat a seed in about eight to ten seconds. The Great and Blue Tits take the seed away and, when in sight, seem always to eat the seed and not cache it. Usually Greenfinches pay a short visit, consuming around five or six seeds. Occasionally one or two will stay for up to five minutes. So, over a day, the other birds consume a significant proportion of the seed taken.

This is the point at which Chris Packham would no doubt use a camera or six to record a whole day's activity to come up with a scientific answer to the question "which birds take what proportion of the seed?". I do not have access to his resources, so I will probably never know how many of the 7000 seeds a week are taken by Coal Tits. The answer is obviously going to be a lot of seed. I have already observed that Coal Tits visit at such short intervals, that a high proportion must be being cached. I have also read that about 80% of seed cached is never found again.

So where does this lead me? My thoughts turned to the ecological effect of Coal Tits in a woodland. At this time of the year they will be turning their attention to alternatives to their spring/summer insect diet. Each bird could potentially cache at least 1000 seeds over the autumn, most of which will not be found again by the depositer. This undiscovered cache will therefore be available to other foraging animals, including other Coal Tits of course, but also benefitting small mammals such as mice and voles.

Although many seeds will be found and eaten by something, a proportion will remain to germinate and a few of these will produce new plants. There is a tendency to show food chains as straight lines from plant to ulimate preditor. In the case of Coal Tits, I suppose we would have something like plant, seed, Coal Tit, Sprawk. The reality is more complicated as the Coal Tit may, in part, be responsible for the existence of the plant. It is also involved in providing food in the chain, via its cache, for other animals.

So for anyone wondering if anything much is going on in a birder's brain as s/he sits for hours watching and waiting; some of us at least are pondering the amazing complexity of our natural environment and the incredible variety of plants and animals for which it provides a home.

No comments:

Post a Comment