Friday, 24 October 2014

Why do we feed garden birds?

ResearchBlogging.orgA couple of Goldfinches came to the nyger seed feeder. A Blackbird was sat on the rowan, which barely has any berries left, while a Dunnock and a Robin pecked at the bits of bread left by a Woodpigeon and a couple of Collared Doves visiting earlier. Yes, I do put food out for the birds. Bread crusts that the kids leave behind after breakfast, mixed seeds, peanuts. I stopped stocking the bird table with seeds though, as Woodpigeons and Collared doves wolf them down in a sitting.
 But I do feel conflicted putting food out for birds. It is good for us or is it good for the birds? Yes, I do enjoy watching the birds coming to food I put out, but I much rather watch the birds that come to the garden for its intrinsic value: long-tailed tits hunting aphids in the bushes, blue tits looking for spiders on the wall, or blackbirds feeding on the rowan and cotoneaster berries or the fallen apples, or swifts and house martins flying overhead hunting insects. I also worry that I don't clean the feeders as often as I should.
 A recent survey in New Zealand revealed that introduced species were more likely to benefit from supplementary feeding than native ones (House Sparrows and Blackbirds were the top species visiting gardens), questioning the conservation value of bird feeding. Here, we have proportionally fewer introduced species in gardens, but most of the birds which benefit from supplementary garden feeding have increasing of stable populations. Even if a few species in decline regularly come to gardens*, is this really the way we want to help them? providing a few scraps instead of good habitats?
 We spend a lot of money on feeding birds. According to the BBC, about £200 million is spent every year on bird food and bird feeding in Britain. About a third of us regularly top up our bird feeders. To give you an idea of how much money this is, compare to the 'meagre' about £25 million annual income of the Wildlife Trusts. Imagine how much real conservation could be done with this money. Wouldn't it be better if we spent our collective money converting the same surfaces of land that we use to grow bird seed into new meadows, woodland and wetlands bursting with wildlife?
  There are also costs to birds associated to giving the birds supplementary food, amongst them disease. Dirty bird baths and feeders can transmit disease. Trichomonosis and Salmonella outbreaks might have been responsible for the recent declines in Greenfinch, Chaffinch and House Sparrow populations.
 Supplementary feeding has some interesting consequences. We are basically generating a new, often reliable food source, often during winter, when birds may find it difficult to find food. Birds are adaptable, and have started using this resource. The Goldfinch has spectacularly increased in numbers as a garden visitor. In the 90s it was present in less than 15% of gardens, while now is reported in about 50% of them. Much of this increase appears to stem from provision of Nyger seed, which is also encouraging Redpolls and Siskins into gardens. Once individuals find, and learn to use a resource, the habit is transmitted to the next generation. Another unforeseeable consequence of supplementary garden feeding is the recent change in migratory habits of the Blackcap. Blackcaps have become a common winter visitor in gardens. These birds are migrants from Germany, which move to the UK instead of the Mediterranean (I've covered this before in The Ratting Crow). We are indeed changing birds in unexpected ways by feeding them.
 The same New Zealand study I mentioned before examined the motivation behind bird feeding and found that people feed the birds because birds give them happiness (50% of respondents). As feeding birds brings us joy, it is unlikely to stop. I do look forward to the visiting Goldfinches. This summer, they brought a new generation of fledged young to the feeders, which will likely carry on visiting for years to come.

*Common declining garden species as found in the BTO Garden Survey Results include House Sparrow, Starling, Greenfinch and Song Thrush.

More information
Galbraith, J., Beggs, J., Jones, D., McNaughton, E., Krull, C., & Stanley, M. (2014). Risks and drivers of wild bird feeding in urban areas of New Zealand Biological Conservation, 180, 64-74 DOI: 10.1016/j.biocon.2014.09.038

Thursday, 23 October 2014

Woodpigeon fledgling chasing parent for food

I saw a young woodpigeon fledgling by the pond today, it shook its wings occasionally like young to when they demand food and I noticed an adult was nearby. The young one caught up the the parent and touched its bill, to which the adult responded by regurgitating food. The young continued chasing the adult for quite some time, regularly managing to be fed. The size different between both is quite noticeable in the top shot. 
 Young woodpigeons are much drabber, greyer than adults, without a pinkish tinge. Legs and bill also lack the red and orange hues of the adult, and the bill does not have a developed cere or operculum, the swollen covering covering the base of the bill. Young woodpigeons have dark eyes and lack the parents neck markings. Although their smaller size and black eyes makes them similar to a Stock dove, they still have the trademark white woodpigeon wing-bar.
A side view of the fledgling


I also took a video of the sequence. 

Thursday, 2 October 2014

Broken Wing

This has been an unusual year for Canada Goose in the park. Usually, a flock visits during the winter, roosting elsewhere and returning every morning to enjoy the bread and food given by people. Some time during last winter, one of the geese got injured, its right wing hanging a bit loose on the side (I first noticed it the 16th of January, the photo above is from the 16th of March). The injury, at the base of the wing, prevented it from flying, and it must have happened in the park, maybe due to a collision with a tree branch or a fight with a dog. The bird seemed content, fed well and recovered enough for the injury to be almost unnoticeable. But when the flock decided it was time to depart for the breeding grounds, at mid February, the lame goose stayed behind. All through the summer it has been alone in the park, joining the mallards during feeding time, and probably roosting on the little island at night. I felt for him as geese are such sociable birds.
Part of the Canada Flock returning from the roost in the morning
 The flock of Canada Geese returned last week. I searched for the lame one in the pond, but failed to spot him, it must have mingled with the rest of the geese. I wished I had been there to watch his reaction to, first, the distant honks of the approaching flock, and then to the geese themselves once they landed. Then a couple of days ago, early in the morning, I spotted him with two others, just before most of the flock returned. Again, today, the goose was with a female before the main flock returned. They followed each other closely, like a pair of geese would do. Could it be that this was/is his partner? Geese form strong partnerships and bond through the year, and for many years if not for life. They also recognise many individuals in their flock, including their past offspring. The female goose is actually staying to roost with the lame goose at night, instead of following the flock. Maybe when the migratory urge kicks in spring she will leave with the flock, but maybe not.
The lame goose in the background, with a partner on the 30th of September
My peak count per visit graph for Canada Goose in Pearson Park. If you try you can see a tiny green bar between week 8 and week 39, corresponding to the lame goose. Created with BirdTrack.

Friday, 13 June 2014

Blue tit family and Sycamore aphids

I heard the rasping begging calls of blue tit fledglings coming from a Sycamore tree, which I find it is a very common occurrence. As I approached I noticed clouds of Sycamore Aphids cascading down from the tree as the adult Blue tits moved about, searching for the aphids themselves and green caterpillars (above). It was a very impressive spectacle as the light hit the aphids and amplified the effect. The tree leaves were thickly peppered with aphids, and fledglings were having a go at finding food by themselves. One of them found a long green caterpillar and wrestled with it for a while until it was able to swallow it.
I tried to capture the density of aphids flying off around the tree in this photo.
The evenly spaced, winged Sycamore aphids (Drepanosiphum platanoidis)
A fledgling begging for food.
The adult cuts the caterpillar in half before feeding the fledgling.
This young one had caught a caterpillar on its own.
You can watch one of the adults foraging and the aphids flying off here.

Friday, 16 May 2014

Offspring recognition in Starlings

ResearchBlogging.org The first Starling fledglings joined their parents in the lawn of the park this morning, running behind their parents begging for food, with a cacophony of calls. Starlings are highly social birds, they like to feed together so the chances are that the still dependent young will join unrelated young while still expecting to be fed by their parents. Starlings have synchronised egg laying so that many young fledge on the same day. While they are at the nest, parents do not need to particularly recognise their offspring individually, as they are likely to be the young in their own nest. However, how can they make sure they recognise their offspring from others so that they feed their own young after they fledge?
  Every year, a week or so before the fledglings leave the nest, adults start using a harsh call 'charr, charr!' (above, listen here) and the by then loud voices of the young can be heard responding from inside the nest. Why, I wondered, do they do this?
 Linda van Elsacker, Rianne Pinxten and Rudolf Frans Verheyen carried out experiments in nest box starling colonies in Antwerp (Belgium), either swapping broods of different ages for a day (Exchange experiment), or offering a choice between their chicks and alien chicks in nearby nests (Choice experiment), or swapping the nest by an empty one and relocating their nest containing young at a certain distance (Search experiment) at different chick ages.
In their choice experiments, carried out when young were 5, 11 and 16 days old, they showed that parents accepted and fed strange chicks until they were 16 days old, as shown by the weight gain of the chicks. In contrast, most parents were able to recognise their chicks when they reached 19 days, ignoring the strange ones completely, and this behaviour was found in all parents when chicks were 20 days old. So by this age adults were able to recognise their chicks.
In the search experiments they showed that the ability of parents to locate their offspring increases quickly and by the time chicks reach fledging age (20-22 days) old 97% of parents searched for and relocated the moved nest containing their young within an hour of the nest having been moved.
 The constant calling by parents and offspring in the days before fledgling might be a way of reinforcing this recognition. So, by the time the offspring are ready to fledge, and then mingle with other chicks, parents are able to recognise their offspring, presumably by their calls.

More information

Frans Verheyen, R., Van Elsacker, L., & Pinxten, R. (1988). Timing of Offspring Recognition in Adult Starlings. Behaviour, 107 (1), 122-130 DOI: 10.1163/156853988X00232

Chaiken, Marthaleah (1992) Individual recognition of nestling distress screams by European starlings (Sturnus vulgaris). Behaviour : 139-150.
Young starling looking for food this morning

...and chasing its parent begging.


Monday, 12 May 2014

Moorhen nest building

The Moorhens seem to have settled in the park, with a pair having secured the island as a territory. Next to the island there is a large fallen branch that has been used to nest before. One of the moorhens was tidying the nest, trying to bring branches sticking up into the nest structure.
 You can watch a short clip of her activities here:

Tuesday, 6 May 2014

Fledglings

In the last couple of days I've come across a number of resident species with fledglings. Blackbirds were first, a short-tailed adventurous chick calling for food in the park, last week (below) and today (above) a Robin yesterday and a Song Thrush and Dunnock today. As the youngsters jump from the nest, they have to face a steep learning curve, they are more or less naive to predators, so in these days between fledgling and independence from parents they need to learn about them and also perfect their foraging skills, usually while they follow their parents, begging.
 Magpies and Carrion Crows start showing an interest on trees and bushes, listening for calling chicks, so the alarm calls of the adults, associated to the different predators are part of the learning process. The first mallard brood in the park has already disappeared, probably due to predation by Herring and Lesser-black backed gulls.
Blackbird fledgling, 29/04/2014, from the same brood as the top photo, today.
These goslings from a local park already show a great interest in people, usual food providers here.
Young Robin
A sleepy Dunnock fledgling
A song thrush finding food for its youngster...
Young Song Thrush fledgling and busy parent.
A Magpie in search of nests or young birds in the undergrowth.
A Herring gull in the park having mallard for breakfast this morning.