Wednesday, 3 December 2014

Gritting greylag geese

Birds that feed on fibrous or hard food of vegetable origin often swallow sand or small stones ('grit'). Grit accumulates in the gizzard or crop, and together with the muscular action of the crop it helps macerate their food facilitating digestion and increasing food processing rate. The limited size of the gizzard means that herbivorous birds need to spend time just processing food, waiting until the gizzard empties, before another foraging bout. Grit can be ingested accidentally with the food or purposefully, by visiting places where it is easy to find. Wintering flocks of Greylag goose in Doñana National Park (Spain) visit sand dunes to ingest sand, and their crop can hold up to 10 g of sand.  Birds can adjust the amount of grit to their diet and in turn, crops containing more grit become more muscular, flexibly responding to the demands of different coarseness or amount of fibre in the diet.
 While watching the flock of wintering geese in my local park, I noticed them stopping in a bare area. First I thought they were feeding on the small tufts of grass there, but when I looked closer I realised they were ingesting grit. They spent a few minutes doing this, and then moved onto the grass to feed. The distinctive individual with a white head (above) serves as an identifier for this flock. I have seen him or her both at East Park and Pearson Park.
A pair gritting together.
Here is a short video of the behaviour:



More information
Amat, J. A., & Varo, N. (2008). Grit ingestion and size-related consumption of tubers by Graylag Geese. Waterbirds, 31(1), 133-137. here.

VerCauteren, K. C., Lavelle, M. J., & Shively, K. J. (2003). Characteristics of grit in Canada goose gizzards. Wildlife Society Bulletin, 265-269. Here.

Friday, 21 November 2014

In the wrong flock

Although I wouldn't consider Pink-footed Goose (also known as Pinkfoot) to be an urban bird, it is a species that I regularly see. Skeins of this migratory geese, announced by a chorus of high pitched calls, regularly fly over the city in October and March, on their way to and from their breeding headquarters in Iceland and Greenland. Occasionally, however, a straggler will turns up with Greylags in local parks, allowing a closer look.
  On my way to work, walking through the park, a flock of Canada Geese and another of Greylag geese were about. While counting them I noticed a much smaller goose, a Pinkfoot, amongst the greylags. They have small bills, marked with pink, much darker head, contrasting with the slaty back. I think this individual was a young bird born this past summer, as you can see two types of feathers in its flanks and back, as the larger adult feathers, with a pale edge, have started to grow. The furrows that adorn the neck of adult geese are not yet sharply defined. The goose wasn't welcome and was often lunged at by the Greylags. Surprisingly, it was quite relaxed in the park, despite proximity to people, and it got very close to me as it followed the other geese across the lake and then to the grass to feed.
 I other occasions when had previously seen other Pinkfoot with greylags, it was also young birds. I wonder if leaving with your own species as the flock departs takes some learning. Geese need to reach a consensus before leaving as a flock, a decision that takes place by increasingly noisy vocalisations and movements of the birds of the flock when they are ready to leave. If a young bird misses the cues, it will fail to take off might miss the flock altogether, becoming stranded possibly with another geese species. Geese have long lives and move about, so most likely, while following the greylag flock in its travels, it will eventually meet a Pinkfoot flock and the young bird will be reunited with other members of its species.
A Greylag drives the pinkfoot away from its partner

Walking towards the grass. The difference in size between both species is evident here.

Sunday, 9 November 2014

Walton Street crows

We went to Walton Street market and car boot sale this morning and I couldn't help but notice the crowds of Carrion Crows. At least 50 individuals were about, on van and car roofs, atop flood lights,
 and walking amongst the huge puddles left by yesterday's rain.
Some patrolled just over the paths, elaborately flying slowly, sometimes almost hovering - in black-headed gull style - scouring the ground.
Soon it became apparent what they were after. No, they weren't hunting for antique bargains, but taking advantage from the fast food bonanza that inevitably follows human crowds.
Crow on roof van. 
A starling passed too close and made him jump
I missed the wing tip in the phot, but I like the shadow of the crow
I watched as one individual landed on the roof of a van, triumphantly holding half a hot dog sausage in its bill.
The remainder of the hot dog was being dealt with a few other crows: a dominant one pushed another aside...
...and quickly picked up the other half of the sausage in its bill, before flying away
while the other, less fortunate crows contented themselves with bread smeared on ketchup.
We associate scavenging behaviour with dirt, rotten food and germs, but I doubt the hot dog had been on the ground longer than the five-second rule allows, before it was cleared up, taken away by the crows.
But, occasionally, the bin man gets there first. Crows watched him picking a paper bag...
...but leaving some food behind, which was quickly dispatched
There were many gulls and starlings about, but I didn't see them take advantage of the market food. Crows appeared bolder, and cheekier than in other places, maybe they are all locals used to take advantage of the markets - and Hull Fair - and are used to people. This one spent some time checking itself out in the wing mirror of a car.
The it jumped to the roof and spent some time watching from this vantage point.It allowed me to approach close enough for a portrait (top shot)
 After filling their tummies, some crows took turns in the puddles for a bath.



Wednesday, 5 November 2014

Into the eye of the winter herring gull

 The resident pair of Herring gulls are back at the park. One of the individuals (above) has its full winter attire with a streaked grey head, which gives it a particularly stern look. The other one, which seems smaller (maybe the female?) still has a very white head. A young of the year is also about.

Spotting the Sparrowhawk

The pigeon flock in the park took off all of a sudden, like a loud clap. In the silence that followed, I looked up: The male Sparrowhawk flew into the tree tops, I managed to see where it landed, high up in a sycamore. The leaves made it tricky to have a clear view, but I managed a few shots. When I find a predator by interpreting the behaviour of their prey I get a satisfying 'Dr. Dolittle moment'. The rattling call of the crow that gives this blog its name, or the alarm call of the blue tit have pointed me to many a Sparrowhawk. The Feral Pigeons are probably safer in flight than sitting on the cafe roof when a Sparrowhawk is out hunting, so they take off as soon as they see the raptor in flight.

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.