Wednesday, 28 November 2012

Communal bathing

Yawning is known to be contagious in primates, but having a good bath is something birds often will do in company. As soon as one starts, others nearby, often of the same species, will copy. Bathing washes and cleans feathers, and afterwards, the bird dries up by shaking tail, wings, body and head and then proceeds to oils the feathers by spreading over them a secretion produced by a gland above its tail. A few days ago, I watched these Mallards bathing and preening in sequence with some enthusiasm, today it was some Great Black Backed Gulls, the Sparrows in my garden often do it as well.
Male Mallards have good reason to keep their feathers in top condition, as they will be already paired or looking for a partner at this time of year. Maybe bathing is also an opportunity for showing off.

Wednesday, 21 November 2012

Bottoms up!

This is probably one of the most familiar duck behaviours. Mallards often 'upend' to feed, submerging the anterior parts of their bodies and keeping their tails pointing up, while keeping their balance paddling with their feet -  a behaviour most kids find hilarious. Although it is not a universal duck feeding method, Mallards are amongst the experts. Mallards are dabbling ducks, they obtain most of their food from near the surface. Upending allows them to reach just a little bit deeper and feed at depths not used by smaller dabbling ducks but too shallow for diving ducks. In contrast to smaller dabbling ducks, mallards and other large dabbling ducks can afford to upend as their large size allows them to reach deeper and to remain submerged for longer.
Proportion of Mallards feeding using different feeding methods (from Green, 1998).

In a comparative study of duck feeding behaviour, Andy Green found out that neck dipping and upending were the predominant feeding methods in Mallards. Ferruginous ducks, a species of diving duck, did not upend and barely used the neck dip, diving was overwhelmingly the most commonly used method. 
 You can watch Mallards upending in this short video:

More information
Andy J. Green (1998). Comparative feeding behaviour and niche organisation in a Mediterranean duck community Canadian Journal of Zoology, 76, 500-507 : 10.1139/z97-221

Tuesday, 20 November 2012

Greylag portrait

I took this photo last monday in a local park. I can't stop myself photographing Greylags, definitely a top bird for me, and I feel lucky that these geese are so approachable, most if not all of them of feral origin. The flock was watchful for dogs, and took off shortly after, but this handsome individual looked straight to the camera while posing nicely.

Saturday, 17 November 2012

The Common Pochard

Common Pochards, Aythya ferina, are common wintering ducks in the UK. I find intriguing that most of the birds in my local park are males. However, this is the case for the whole UK winter population, with males outnumbering females in a 2:1 ratio. In sites where supplementary food is given this biased sex ratio can be much more extreme (5:1). Females appear to migrate further south than males, and the reason for this could be that males are much more aggressive towards females than they are to other males. Confronted with this intraspecific competition, females move on to areas where there are fewer males. Males might benefit from shorter migration distances by coming back earlier than females to establish breeding territories.

  Pochards, unlike other birds, seem to have the same pattern of activity between day and night, they are cathemeral. Bouts of feeding are followed by bouts of sleeping day and night, and they are often found resting in flocks during the day (they still sleep about 50% of the time).

  In the winter, these diving ducks feed mostly on seeds and fuiting bodies of aquatic plants (Chara, Nitella, and Potamogeton being a large fraction of their diet). Their distribution is limited by their diet, as they require large bodies of water with good population of aquatic plants. They feed by diving and up-ending, and, they probably rely on the sense of touch to feed, which may explain they do not need light to feed.
One of the few photos I have got of a female Pochard, in the company of Tufted ducks.

Thursday, 15 November 2012

Carrion crows dunk their toast

ResearchBlogging.orgI had the chance of watching a Carrion Crow dipping bread in a puddle this morning. The crow deliberately walked towards me holding a piece of bread in its bill as it approached the water. It was obviously so preoccupied with the task that took no notice of me taking the camera clumsily from inside my backpack. I stayed still and avoided eye contact while the crow carefully placed the bread on the edge of the puddle and nibbled a few bits. Immediately after, it decided to walk around the puddle turning a few leaves and stones over - even a leaf that was, literally, almost touching my feet. After this, the crow run to the bread across the puddle and ate it. You can see its gular pouch filling and there is little bread left on the photo above taken at the end of the following video.

I had previously seen just once this bread-dipping behaviour. While feeding the birds in the park with my daughter, the pigeons kept stuffing themselves on the bread. The whole chunks of bread inside the pigeons crops made their necks stick out funnily. A crow turned up, fetched some bread and then walked towards the pond edge, dipping the bread and eating it while wet and soft. Today's crow was more interesting, as it waited for a while before returning to the bread, as if allowing it to soften.

  Crows are amongst the few animals able to learn to wait to receive a reward. Dunking bread is equivalent to cooking: there is some food preparation involving costs: time, effort and potential food loss (another crow might come while you wait and steal your food) before you can enjoy an easier to eat food. Overcoming the impulse to eat the raw food straight away is a prerequisite for cooking. Young children are incapable of the self-control involved in having to wait for a reward - they are naturally impatient - and the ability develops slowly, but great apes are also able to control an impulse to eat a reward in exchange of delayed rewards of higher quantity or quality. Crows join humans and great apes in being able to delay gratification. Crows might be predisposed to waiting for a reward as they do routinely hoard food for later - leaner - times. Valerie Dufour and colleagues carried out experiments on captive Carrion Crows and Ravens that demonstrated delayed gratification. They showed the crow a desirable item (grapes, cheese or sausage) but gave them a less desirable food (bread). Then, if the crow waited for a length of time and returned the bread, they were given the tasty reward. The crows - at least some of them - were able to wait up to five minutes to exchange the bread to obtain the desirable reward. They were also more willing to wait longer for their favourite item (usually sausage).

Figure 1. General capacity to wait: percentage of successful exchanges according to the length of waiting period for individual Carrion Crows (from Dufour et al 2011).

  In the video sequence above, the crow carries out a series of activities before eating it (drink water, lift a few leaves and turn stones). This is reminiscent of displacement activities to alleviate a frustration. The experimental Carrion Crows, especially those waiting for longer, also carried out such displacement activities while waiting for the desirable reward (placing the bread on the ground, pacing up and down their cages, or hiding it repeatedly)(you can watch some videos of the experiments here).

More information

Dufour, V., Wascher, C., Braun, A., Miller, R., & Bugnyar, T. (2011). Corvids can decide if a future exchange is worth waiting for Biology Letters, 8 (2), 201-204 DOI: 10.1098/rsbl.2011.0726

Sunday, 11 November 2012

Wandering Waxwings

ResearchBlogging.orgI have litte interest in watching birds swept away from their native grounds by a tropical storm, or inexplicably lost and found far away from their usual migratory routes. Waxwings are different, and I have been wanting to see them for years. They might be rare, or not present in great numbers every year, but the UK is part of their distribution range. The last couple of days, I have been popping in a local supermarket carpark to watch a large flock of these amazing birds. Bohemian Waxwings, Bombycilla garrulus, as other boreal bird species - like Crosbills, Siskins and Redpolls - do not fit into a regular migratory pattern, they are instead irruptive migrants. It is thought that the species common name, Bohemian, comes from these wandering habits. In irruption years, many thousands of individuals flock and wander well south of their summer grounds in the the Russian and northern Scandinavian taiga making it to the UK. Flocks then move nomadically in search of food, as it is not cold winters what prompts their movement, but unpredictable food resources. Irruption years in Waxwings correlate with poor crops on fruit and berries in their northern grounds following a good fruiting year. Waxwings are highly frugivorous birds, their exclusive diet in the winter consists of berries and fruits: Rowan, Hawthorn, Cotoneaster, Mistletoe, Rose Hips and many others both wild and cultivated. The main resource, Rowan berries, fluctuates erratically across years in their summer grounds, as Rowan is a masting species, as fruit production is synchronised in the population and totally fails some years. During these poor fruit years, Waxwings initiate their movements earlier in the year, and therefore earlier arrivals of waxwings indicate that it will be an irruption year.
 During irruptions, waxwings carry on moving through the winter as they deplete their food resources locally, and they are wanderers all year round, with little chance that they will return to the same areas where they were born in the following summer. This winter is going to be one of those irruption years, and the Waxwing invasion is well underway.
 Waxwings are surprisingly small birds, similar in size to Starlings, to which they also resemble in flight, as they flock and have pointy, triangular wings. At close range there is no mistaking them, with their soft plumage, characteristic crest and 'zorro' mask. At even closer range, you might get to see the striking bright scarlet waxy drops and yellow streaks adorning their wings. They do look smart.
 As most fruit eaters, Waxwings need to eat a large number of berries to survive - an estimation was double their body weight in berries. A flock can quickly strip down a tree. When not feeding, they like to sit atop trees, preening and just looking around, while constantly chattering, a pleasing cricket-like and jingly call.

A large flock of Waxwings resting and preening.
The top of this Rowan has already been stripped, but there are still plenty of berries at the bottom of the tree, which are harder to reach 
A circling flock of Waxwings deciding where to stop
 These three were looking up nervously, might well have been keeping an eye on the Sparrowhawk soaring above them.
The flock I was watching was resting on a Rowan tree and the birds were not quite daring to do to the bottom of the tree to start eating. They increased the rhythm of they calls like they were agreeing on something, and took to the wing. I am so pleased I finally managed to catch up with them. Bon voyage!

More information

Barbara and David Snow (1988) Birds and Berries. T & AD Poyser. 268 pp.

Ian Newton (2006) Advances in the study of irruptive migration. Ardea 94, 433-460.

Koenig, W., & Knops, J. (2001). Seed-crop size and eruptions of North American boreal seed-eating birds Journal of Animal Ecology, 70 (4), 609-620 DOI: 10.1046/j.1365-2656.2001.00516.x

Saturday, 3 November 2012

Food hoarding Coal Tits

ResearchBlogging.orgOne of the things I enjoy the most about watching birds is that even familiar species often surprise me with behaviour I have not seen before. I watched birds feeding on seed and peanut feeders a few days ago. A pair of Coal Tits, Periparus ater, showed their usual energetic prowess: a constant back and forth between the feeders, quickly snatching a seed and then flying away, to return within a few seconds later for another one. This time though, I could see where the Coal Tits were going and they were not flying away from the feeder to eat their seed in solitude, without the hassle of the larger birds, instead, they were storing the seeds: on the ground, pushing the seed into the soil, in the cracks in the pavement, on branches, in a conifer bush or in pots.
 Although corvids are more widely known to store food, food storing is common in Tits (parids). Marsh, Willow and Crested Tits are regular food storers, (although Great and Blue Tits are not). Parids store insects and other invertebrates (after decapitating them), seeds and nuts. They might store hundreds to thousands of items per day, using a different hiding place per item and even covering the hidden item with a piece of bark or stone. They might store the items a short distance away from where they were found, or up to 100 m away. They may often retrieve the food after a few days, but possibly much longer as not readily available food items (such as caterpillars) are often seen consumed by tits in the winter. A Japanese species, the Varied Tit, can feed its nestlings up to 5% of stored seeds from the previous summer-autumn. Parids display good memory not only spatial, to go to the exact place where the food was stored, but also to remember which caches have already been retrieved. Food storing in such small birds might contribute to survival when food is strongly seasonal or unpredictable and it can be retrieved when its consumption will make the largest contribution to survival.
 I managed a very short clip of a Coal Tit storing a seed.

But I wasn't the only one watching. This blue tit was also very interested in the Coal Tits.
After watching it, the Blue Tit came right up to a Coal Tit about to hide a seed - it is just visible in its beak in the photo below. After a brief hesitation, the Coal Tit decided to go somewhere else and left just after I took the following shot. Sorry about picture quality today, but all the shots were taken through glass.
More information
David F Sherry (1989). Food storing in the Paridae Wilson Bulletin, 101 (2), 289-304