Saturday, 27 February 2010

On Sparrow Bibs

Male sparrows are now beginning to show the urge of starting their breeding territories. I have seen several males chirping constantly from house eaves, a common nest site. When chirping, sparrows show off their fluffed up black chest bib. Sparrow bibs vary considerably in size between individual sparrows.

Figure showing variation in badge size in Male House Sparrows (from Moller 1987). See also the photos below.

Research has shown that bib size functions as a 'badge of status' and individuals with large badges enjoy a dominant status in the flock. Large badge individuals also obtain earlier mates as females prefer them and enjoy more reproductive success. Males with large badges seemed also better at defending their females from sexual harassment in multi-male chases. Large badges carried a cost though. Sparrowhawks, the main predators in the study took males with large bibs more often than males with small bibs during the autumn. The explanation was than high reproductive success had a cost in the condition of the bird at the end of the season. The study showed that sexual selection - female choice - and natural selection through predation acted in opposite directions in determining bib size.
A large bib male in my garden flock
A small bib male
Moller, A.P. 1987. Variation in badge size in male sparrows Passer domesticus: evidence for status signalling. Animal Behaviour, 35:1637-1644. here.

Moller, A.P. 1989. Natural and sexual selection on a plumage signal status and on morphology in house sparrows, Passer domesticus. Journal of evolutionary Biology, 2:125-140. here.

Thursday, 25 February 2010

On zebra mussels and tufted ducks

One of the most common diving ducks around here is the handsome Tufted Duck (Aythya fuligula). The male striking black and white plumage, long tuft of feathers at the back of their heads and yellow eyes makes them quite distinctive. Females are all brown and have only a tiny, but clear tuft. Reading about tufted ducks I came across some research suggesting that the spread of a non-native invasive species, the Zebra Mussel (Dreissena polymorpha) in the UK in the last couple of centuries could be linked to the increase in Tufted Duck numbers.
 Tufted ducks dive up to 5 m of depth to feed. They eat mostly zebra mussels where they are available, whereas in places where zebra mussels are not widespread, their diet is more varied, with crustaceans, insects, seeds and some molluscs. The mussels, which are of small size are swallowed whole and crushed in the muscular gizzard. The small mussels are sucked and filtered, while the larger ones require more manipulation.
and down it goes!
More information
Olney, P. J. S. (1963). The food and feeding habits of tufted duck Aythya fuligulaIbis105(1), 55-62. here.

Joep J. De Leeuw and Mennobart R. van Eeerden 1992. Size selection in diving tufted ducks Aythya fuligula explained by differential handling of small and large mussels Dreissena polymorpha. Ardea 80:353-362. here

Tuesday, 23 February 2010

Changing Heads

The first Black-headed gulls honouring their names have now appeared. The dark head is their summer attire and this makes them much easier to tell apart from the white headed, and very common, Common Gulls. This winter I have been testing my ID skills on flying city gulls. Black-Headed gulls are much more keen to pick scraps from the ground in busy streets and their flight is quite bouncy. The white front of their wing primaries can also be very obvious. I found the almost completely molted individual above in a local park on Valentine's day, and later, in a flock, only a couple of individuals have completed the molt, while most are on their winter plumage.

Saturday, 20 February 2010

Take a bow

There is a lot of Woodpigeon activity these days. I can hear the slow, five-syllable song continuously repeated from the aerials and trees in the street in the morning. The clapping of the territorial display, an exhibition flight, in which the Woodpigeon rises high noisily clapping its wings and then glides down in a circle with wings outstretched and kept horizontal. On a roof yesterday, a male and female were engaged in more active courtship. The pair makes these little jumps as they get closer to each other and they engaged in feeding, usually the male feeding the female.
This couple sat together for a while, but if courtship proceeds the male engages in a 'bowing display, with exaggerated, ritualised slow bowing until its beak touches the ground while lifting its tail and opening and closing it like a fan facing the female. The male calls at the same time. While singing the male ruffles his neck feathers showing off its side white and iridescent patches. If the female is ready she crouches opening its wings and the male quickly mounts her, otherwise, she will move away or try and peck the male or even fight him off with wing strokes.
 The following YouTube video shows a male courting a reluctant female.

Saturday, 13 February 2010

Greylag Geese watching

 In the last couple of weeks, a small flock of a dozen greylag geese has started to come to the local Park. Greylags are one of the most interesting local birds to watch. Once they land, the orderly formation breaks and pairs separate and noisily settle scores before starting their feeding with ritualized neck posturing. Despite being in a flock, pairs are usually quite easy to spot, they follow each other and the gander is slightly larger than the goose. When showing aggressiveness, one of the pair members lowers its neck and shows the beak to its opponent, with the partner following close. On quiet times, where no people are feeding the ducks, greylags head up to the large grass spaces of the park to feed. These are no wild geese, if you show some interest in them, they are likely to come closer to check if you have scraps, or even come right to you to demand some depending on their personalities. To watch them doing what if comes naturally to them you need to feign indifference. Today I watch six of them grazing.
Konrad Lorenz, the Nobel prize, carried out long term behavioural studies on hand-reared greylag geese to allow close approximation. His geese - which were individually named - lived free but did not migrate, so he could study them year round. Lorenz describes geese behaviour in detail in his book 'Here I am - where are you?' Lorenz first discovered the phenomenon of imprinting on geese, by which newborn birds attach themselves to the first moving object they see after hatching. The description of his first, serendipitous, realisation of imprinting is quite moving: 
'After the first gosling had hatched and dried, I was unable to resist the temptation of removing the delightful creature from under the foster mother and taking a closer look. As I did so, it gazed at me and soon began to utter its single syllable lost calls [...] I answered with a few comforting sounds. [...] Eventually, however, I had enough of this babysitting and placed the gosling back under the wings of the brooding domestic goose and started to leave. I should have known better.' 
The gosling started making distress calls and when Lorenz starts moving away, it follows him. Lorenz did a lot of babysitting from then on! 

The Greylag goose triumph ceremony (from one of Lorenz's papers on the behaviour of the Greylag geese).

Wednesday, 10 February 2010

The timid dove

You can consider yourself lucky if you have watched Stock Doves (Columba oenas) around. Compared with the obvious Woodpigeons and Collared Doves, and the tame ever present feral pigeons, Stock Doves are shy and unobstrusive. Their general dove-like appearance makes them almost invisible despite being relatively frequent in towns and villages. Although dull-grey from a distance, this dove is quite delicate at close range. It is shorter tailed and smaller than the Woodpigeon, being similar in size to the feral pigeon, but its dark wing bars are thinner and shorter and its eyes are dark, giving it a gentle expression. It has got an iridescent neck patch, shining green or violet, and an orange and pink beak. Unlike its relatives, it breeds on holes and therefore tends to occur linked to mature trees in parks and tree lined avenues with large gardens, although it also uses nest boxes (a couple used the owl box in the tree outside our house a few years back).
 Today, a rapid, persistent almost hiccupy cooing (uh, cu-uc! uh, cu-uc!) of a Stock Dove came from the large cypresses next to the park conservatory and a bird alighted on top of a nest box, giving me a rare photo opportunity.

A bill clattering crow

A few days ago I was walking past a wooded area in University when I heard a drumming noise. I though it was a woodpecker, and I stopped and watched. Not at all! A Carrion Crow sitting on a branch made this mute, bill clattering noise - in the most pure Stork style. The mobbing rattle is vocal, but similar in tempo. I managed to take a short video on it, must get round to upload it to YouTube and post it here. When clattering, the crow stood up and fanned its tail. It kept repeating the noise every few seconds. I could see no obvious context - no predators to be seen or even other crows.
More reading on Crow vocalisations here.