Sunday, 17 November 2013

Charming seed predators

 ResearchBlogging.orgI find fascinating that when you seen something for the first time, then the chances are that you would see it again, seeing helps you see more. In the last couple of weeks a charm of goldfinches have been regular visitors in the garden feeders, gorging themselves on nyjer and sunflower seeds. I was watching the goldfinches and taking photos from inside of the house, when I noticed that one of the birds that couldn't get to the feeders was feeding on rowanberry seeds (above), discarding the pulp. This is typical of seed feeding birds like finches. Finches are seed predators, unlike thrushes, that eat the berries whole, passing the seed undigested and undamaged, in their droppings, and dispersing the seed away from the tree in the process.
 There was no mention of Goldfinches in the authoritative 'Birds and Berries' by Snow and Snow. I found a wonderful, if lone, photo on Flickr here and a line in a novel that suggested that this behaviour had been noticed before:
They went down the track through a wood where a flock of goldfinches was feeding on the rowanberries [...]
Tessa Hadley, Accidents in the home, 2002

Today on a walk in the park, I noticed a rowan on a garden and had a look. A charm of goldfinches looked busy on it. I wouldn't have normally had a closer look, but I did. They were feeding on the berries, hanging from the bunches like tits, not one, not two, but the whole flock seemed to be enjoying the berry seeds. The photos from today (below) are atrocious, as it was late and the light very poor, but a record nonetheless. After a while, something spooked the birds, a Sparrowhawk perhaps, and the Goldfinches went quiet and took to the air with a group of starlings and feral pigeons. I glimpsed what I think was a woodcock before if flew behind a roof, powerful wings and long bill, but just for a second. A Blackbird called: 'seee!' from a bush, their air predator alarm call.
 Indeed, a range of finches - including Goldfinches - are reported to feed on rowan seeds occasionally: Greenfinch, Crossbill, Brambling, Chaffinch, Hawfinch, Goldfinch, Redpoll and Siskin. Indeed, for some finches, particularly Bullfinch and Pine Grosbeak rowan seed in autumn can be their staple food. But rowan is a masting tree, where crop is very variable across years, with bumper crop, the 'masting years' interspeded with poor or failed crops in some. In the winter of 2004-2005, simultaneous irruptions of boreal Waxwing, Pine Grosbeak and northern Bullfinch occurred, all three birds liking rowan berries. Bullfinch local movements and irruptions in western and southern Europe have been linked to the strength of rowanberry fruiting crop.

This goldfinch appeared to use her foot to hold the berry in place

  A couple of weeks ago I spotted a juvenile Common Rosefinch, a rare visitor to these shores, feeding on rowan berries

Juvenile Common Rosefinch feeding on Rowan berries. 4/11/2013.

Some finches might use rowan depending on local availability. As this year rowan berries are plentiful and the thrushes have barely made a dent on the crop, Goldfinches and other birds may take advantage of this resource opportunistically.

Pennington, Mike G., and Eric R. Meek. (2006). The ‘Northern Bullfinch’ invasion of autumn 2004. British Birds 99: 2-24.

Munilla, I., and Guitián, J. (2012). Numerical response of Bullfinches Pyrrhula pyrrhula to winter seed abundance. Ornis Fennica, 89(3), 197-205.

Fox, A. D., Kobro, S., Lehikoinen, A., Lyngs, P., and Väisänen, R. A. (2009). Northern Bullfinch Pyrrhula p. pyrrhula irruptive behaviour linked to rowanberry Sorbus aucuparia abundance. Ornis Fennica, 86, 51-60.

Snow, B. K., and Snow, D. (2011). Birds and berries. A&C Black.

Raspe, O., Findlay, C., and Jacquemart, A. L. (2000). Sorbus aucuparia Journal of Ecology, 88 (5), 910-930 DOI: 0.1046/j.1365-2745.2000.00502.x

1 comment:

  1. Your very interesting and informative piece sent me out looking for birds eating berries. I was surprised to find a Great Tit eating the seeds of yew berries, which I had always supposed were poisonous to creatures which (unlike fruit-eating birds) are able to digest them. There's a picture in today's blog
    where I have also put a link to your post.