Sunday, 15 December 2013

A sand bath

A group of sparrows sat by a hedge on a local wildlife reserve. A male came to the ground and started dust bathing on a hollow in the sandy soil, using the same movements bird display when water bathing. Sparrows are known for bathing in water and also in dust. Both are ways to keep plumage in top condition and might help with keeping parasite load reduced. Other birds known to sand bath include wrens, larks, bee eaters, some raptors, hoopoes and chickens, most of them live in habitats where standing water is scarce.
 As bathing, or preening, individuals of a group will join in a communal dust bath as shown in this photo.

Wednesday, 4 December 2013

Treecreepers and mixed flocks

ResearchBlogging.orgAs winter sets in, small, resident insectivorous birds including Long-tailed tits, Great Tits and Blue Tits, Coal Tits, Goldcrests and Treecreepers join in loose, vocal mixed-species flocks that travel and forage together. Why do they eschew from following the saying 'birds of a feather flock together'? Well, first, their small bodies lose heat easily and the days are short, so they need to obtain as much food as possible. On the other hand, the leafless trees makes them more exposed to predation, so, as they feed, they need to be vigilant, keeping an eye on predators and an eye on food, so to speak. Does flocking together help with this challenge: increasing foraging efficiency and reducing predation risk?
 Birds of different species can learn from each other while foraging together: where to find food and how to obtain it. Many of the birds in the mixed species flocks are young of the year, with much to learn. Also, birds spend less time watching for predators while in flocks than when solitary, which allows them to increase the time they can spend looking for food. Despite being 'in a crowd', Individuals in a flock made up of different species may be able to compete less amongst themselves than if they were in a single species flock, as different species often search for food in different microhabitats in trees and bushes. In these mixed flocks, there is a pecking order, with some species dominant, and others subordinate. In Wytham Wood, Oxford, the pecking order was from the more dominant, larger Great Tit, Blue Tit, Marsh Tit, Coal Tit, Long-tailed Tit, and finally the Goldcrest.
  Importantly, the more individuals in a flock, the more eyes and ears available to detect predators. There are similarities in the alarm calls of different species which can allow them to respond appropriately to each others calls.
 Treecreepers are specialists, exploiting the invertebrates found in the little nooks and crannies of tree trunks and thick branches, which they probe with their thin, curved bill while creeping up the trunk aided by their phenomenally curved nails and stiff tail, woodpecker style. This niche overlaps little with other members of the species flocks, and so, they are not expected to benefit from learning from other species or finding new food sources. What do they have to gain from joining mixed species flocks? Arevalo and Gosler investigated the behaviour of Treecreepers joining species flocks in Wytham Wood during two winters. When they found a treecreeper, they noted if if was part of a flock, and if it was, the size of the flock. They also recorded the number of hops and pecks to calculate the percentage of time the bird was looking for food.
 Treecrepers joined mixed flocks more often when the temperatures were lower, so all Treecreepers were found in mixed flocks in the coldest winter months, when flocks were also larger. When part of a flock, Treecreepers were most often found in the main trunk, where competition with other species was minimal, while when solitary, they used internal branches more, so they reduced their niche when in the flock.
Their key result is that the pecking rate was positively correlated with flock size, - indicating that treecreepers could devote more time to searching for food the larger the flock it was in. The pecking rate was not affected by temperature or by the species of tree. This suggests that treecreeper in mixed flocks reduced vigilance, concentrating their effort in foraging.
Overall, this research showed that Treecreepers make a decision to join a mixed flock based on the benefits and costs they are going to obtain. The colder the temperature, the more effort they need to make searching for food, and joining a flock allows them to use a larger proportion of their time feeding, as opposed to being vigilant. At higher temperatures the treecreeper could afford to spend more time keeping an eye on predators, and use a wider niche. The treecreeper, being very cryptic compared to the other species in the flock, might benefit directly from joining the noisy, more visible tits, if they are also less likely to be noticed by a potential predator finding the flock. Arevalo and Gosler also noted:
Treecreepers in flocks were seen to respond to the alarm calls of Long-tailed Tit and Coal Tit during Sparrowhawk attacks by 'freezing' and only resuming foraging after the other species had done so. Play-back experiments with Treecreepers have also shown that they can use information from other species within the flocks in which they usually participate.
You can see this short clip I took a couple of days ago of a Treecreeper showing this 'freezing' behaviour, when a Magpie was nearby. The treecreeper was not part of a flock.




More information

Morse, D. H. (1978). Structure and foraging patterns of flocks of tits and associated species in an English woodland during the winter. Ibis, 120(3), 298-312.

Morse, D. H. (1970). Ecological aspects of some mixed-species foraging flocks of birds. Ecological Monographs, 119-168.

J. E. Arévalo and A. G. Gosler (1994). The behaviour of Treecreepers Certhia familiaris in mixed-species flocks in winter. Bird Study, 41 (1), 1-6 : 10.1080/00063659409477190

Sunday, 1 December 2013

Singing mistle thrush

The local Mistle Thrushes have started to sing in the last few days. This one surprised us on our way home, on a tree in a front garden, quietly warbling, in a tentative way reminiscent of the blackbird's subsong.

A pause in the sun

I watched a Goldcrest busily foraging amongst the golden leaves of a birch tree earlier today. I had not considered taking a photo until I noticed the bird had stopped. It fluffed up its feathers and sat for a rare spot of sunbathing. It has been a lovely sunny mild day today and I is the first time I see this bird sitting still.

Saturday, 30 November 2013

Collared dove

Just a quick portrait post, with this collared dove portrait taken this summer in Pearson Park Wildlife Garden.

Thursday, 28 November 2013

Blackbird alarm calls

For a long time, I have been fascinated with the rich vocal repertoire of Blackbirds. I have recorded their alarm calls and what do they appear to react to, and did some research to find out what was known about them. Here I have compiled what I have found so far in my attempt to understand 'blackbirdese'. I have excluded male song and chick and fledgling begging calls from the post. Given how difficult is to transcribe bird sounds, I have illustrated each call with embedded sonograms and clips from the website Xeno-canto, which contains a fantastic collection of bird calls from around the world, published under Creative Commons licences.
Chink, chink, chink, chink, chink!'
A mobbing call given to owls, kestrel, magpie, carrion crow (and ornithologists checking nests!) which may be followed by attacks. The blackbird is exposed, agitated, flicks tail and wings - which are kept dangling -, from an obvious post (top shot and above) facing the potential predator, very nervous sounding and calling repeatedly and monotonously for a long time. It indicates a moderately aggressive tendency with a low escape tendency, although somewhat inhibited from attacking. Mobbing might be a way of cultural transmission of enemy recognition. Inexperience birds exposed to conspecifics mobbing a predator will join in the mobbing and mob the predator themselves in the future.

Alarm call before roosting or 'chinking'
Territory holding males give a persistent 'chink-chink' calls in the evening, possibly to deter other Blackbirds from roosting in its territory. Other territory holders might join in 'chinking'. This is interesting as it is very similar if not identical to the mobbing call. Is this a dishonest signal 'don't roost here, there are predators around'? or it is an assertion of territorial ownership with a general meaning 'move on'?




Seeee!
The bird sits tense, still, with feathers flat on the body and head. In response to crow and sparrowhawk, whether they are flying or just nearby. Slow, well spaced and high-pitched with open beak (above). Many other birds have a similar thin, high pitched alarm call for threats from aerial predators since the features of this sound makes the calling bird harder to locate, therefore the bird calling does not endangering itself. It has also been called 'hawk alarm', but it is also uttered in response to crows flying overhead or when the nest is threatened. Nestlings react to this call by becoming quiet and still. In experiments using magpie dummies, the parents uttered this call when the dummy was 6-7 m from the nest, while they used the mobbing call when the dummy was very close to the nest. Interestingly, there appear to be differences between urban and rural blackbirds use of this call, as D.W. Snow reported that woodland birds use this call also to humans (the one in the photo above is a woodland bird, so maybe was reacting to our presence), and then it indicates that the nest is very close.



Alarm rattle
A loud, sudden and accelerating outburst, ending on a noisy scream, with the bird flying away. Alarm call when the bird is suddenly startled, also during fights. May starts when the bird is perched but finished in flight. If this call has the same effect on a predator as if an observer disturbs a blackbird at close quarters - it has made me jump more than once - it might give the calling bird a few moments advantage to flee from danger.


Sriii
Also called 'trill' call. A flight or fight intention call. Perched and in flight. It can serve as an appeasement call by a subordinate bird indicating its intention to flee.



Soft call
Also known as 'pok' or 'pook' call, sounds like a soft bark, to me more like 'wow'. Usually from a tree, still or in flight. It is an alarm call to indicate the presence of ground predators, which in gardens usually means the presence of a cat, or a human approaching young or the nest. Fledglings respond to this call immediately by keeping silent and still and looking around, and especially below them. D.W. Snow used a playback of this call to a few day old nestlings reared by him and they acted in the same way.


Chooking
Low pitched, uttered with the beak closed. Anxiety call, mild alarm. Sometimes on its own, sometimes accelerating to the full-swing alarm call in flight. Flicks tail, horizontal body. To people, dogs, cats, etc.  Females use it when disturbed while looking for nest site or nest building. Also used when the bird is foraging in an unfamiliar situation where the bird feels insecure.



Chook, chook, chink, chink, chink
A variant in which the chook combines with chinking as the bird becomes more aggressive or excited.




More information

Snow, D. W. (1988). A study of blackbirds. British Museum, Natural History.

Kryštofková, M., Haas, M., & Exnerová, A. (2011). Nest defense in blackbirds Turdus merula: effect of predator distance and parental sex. Acta Ornithologica46(1), 55-63.

Tuesday, 26 November 2013

Having a very berry time

A few photos from my garden blackbirds taken yesterday, through two layers of glass. The rowan is still loaded with bright, fat berries, which seem to be keeping well. A female, above, about to swallow one. A male, below, had a quiet time after feeding.
This other male (below) has started visiting my garden recently. A quite distinctive individual due to the large white patches on his head. White feathers, often on the head, are quite common in my local blackbirds, but the extent of this individual white markings is the most extreme I've seen around here.


Monday, 25 November 2013

Urban Goosanders

A small group of Goosanders, Mergus merganser, are regular wintering birds in East Park. Not your typical urban bird, you might say, but they can be found in some parks with large lakes during winter, where they may occasionally come for bread (!) (see some great images here). They are stunning ducks indeed, males have black, glossy green heads, with thick, streaked plumage at the back of the head forming a 'bun', and white underside, with a tinge of pink/orange. The tinge in their plumage is caused by carotenoids pigments likely obtained from their diet. Females are grey, with creamy bellies and brown heads with a large fluffy crest at the back. The bill is long and thin, red with a dark hook. They are slim birds and float low on the water, and despite their long necks, they often keep them folded, giving the impression of having large heads.
 Yesterday, we visited the park and initially thought the birds were gone, possibly disturbed by some rowers training in the lake. Finally, we found a pair a the far end of the lake. The male was initially loafing in the shelter of low hanging willow branches near a male Pochard, but then joined the female and started foraging. Despite the urban habitat, they are shy birds, that take shelter near the islands in the lake, and tend to move away from people.
  Goosanders belong to a group called 'sawbills' due to the serrated edge of their bills that help them grip slippery prey, a good feature for a fishing duck. They eat fish, amphibians and aquatic invertebrates, including crustaceans, snails and worms. They rely on transparent water to fish, as they do it by sight, 'snorkelling' like grebes and cormorants do, with their forehead under water before diving propelling themselves only with their large webbed feet. They often probe with their bills on the bottom, to disturb hidden prey. They are also known to engage in communal fishing, where cordons of Goosander will corral fish towards the shallows and dive at unison to catch them.
 This species underwent an expansion during the last century from their Scandinavian range. They only started breeding in the UK at the end of the 19th century and in England since 1941. Now, they breed in upland rivers of Scotland, Wales and Northern England and winter more widely, with the wintering numbers boosted by birds also immigrating from the continent. In the early 1990's, coinciding with population growth in the UK, they started to winter in East Park, often in single figure numbers, with a maximum of about 30. Icy conditions might push them to last remaining open water in lakes, estuaries and sheltered sea shores, although they prefer freshwater.
  Goosanders - in a way similarly to other ducks - are unusual for birds, as males and females have different migration patterns. Most of the Western European drakes, including the British population, migrates to two fjords in northern Norway to moult their flight feathers between June and September, and then return to their wintering grounds in the UK. This male fidelity to their northern moulting grounds might be a cost of the expansion of the Goosander into southern Europe. Females, in contrast, moult later and more locally, late breeding females might moult on their local rivers before their offspring fledges, others congregate in local estuaries with an abundance of fish prey and presence of safe resting areas such as sandbars. It is not known how young birds find the moulting grounds, but association of young birds with more experienced ones in post-breeding roosting sites is a possibility. Pair formation takes place in the wintering grounds, from November-December, in their communal courtship.




The pair of goosanders with Black-headed gulls
Male Goosander 'snorkelling' and showing its 'bun'.
Female about to flap her wings, showing her creamy belly and shaggy 'hair style'.

More information
Hatton, P. L., & Marquiss, M. (2004). The origins of moulting Goosanders on the Eden Estuary. Ringing & Migration, 22, 70-74.

Little, B., & Furness, R. W. (1985). Long‐distance moult migration by British Goosanders Mergus merganser. Ringing & Migration, 6, 77-82.

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.

References
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

Wednesday, 13 November 2013

Watching Tufted ducks

Three Tufted ducks, either female or immature, have settled in the pond of my local park these last days. They have allowed me an unusual opportunity to watch them at close range - as the pond is quite small. They spend much of their time snoozing, preening, and diving. Although the light was a bit poor, the rich colours of the reflected trees on the water made up for it.
 They preen their bellies quite a bit, turning almost on their backs while floating in the water to do so. When they dive, they often do it together, diving one after the other. I had never seen a Tufted duck on land, but today, two of them spent a little time out of water, just by the pond edge, and then it became obvious how different their leg position and body shape is to dabbling ducks.


A good wing flapping after a grooming session

Showing its white belly while preening
Showing the heavy body and legs placed wide apart in the side of their body.

and an edited video of the Tufties

Three black birds turning leaves

The layer of fallen leaves under trees hides treasure for many birds this time of year: earthworms, woodlice, springtails, sprouting seedlings and more. I have filmed three bird species turning leaves in the park, each showing a different style: the Carrion Crow, slowly turning and tasting tidbits; the Blackbird energetically using its whole body, almost jumping, relying on an element of surprise, the moorhens looking like they are removing a nuisance from their way. Here you can watch the three clips.

Blackbird leaf turning




Moorhens leaf turning



Carrion Crow leaf turning

Monday, 11 November 2013

Gobbling up acorns

In the last few weeks it has become apparent that this is an acorns mast year, a bumper year for these seeds - and also for many berries. The evergreen oaks in my local park have not been an exception: Grey Squirrels and Woodpigeons are enjoying this bonanza and feeding on fallen acorns on the ground and the remaining ones in the tree. Today a large flock of Woodpigeons, including many juveniles, feasted on acorns in the park. I managed to record some videos of the feeding activities of the Woodpigeons in the trees and the ground underneath. I find it amazing that the Woodpigeons swallow the acorns whole, presumably their digestive system dissolving the tough shells.
At some point in the sequence, something scared the woodpigeons and most of the flock took to the air. The one I was filming stayed put in the tree, looking up nervously.

Friday, 8 November 2013

Birds and sycamore aphids

Sycamore aphids, Drepanosiphum platanoidis, are Sycamore specialists - and cover your car with honeydew if you happen to park underneath. All adults are winged and sit evenly spaced under leaves. In the spring, sycamores come alive with the calls of hungry Blue Tit fledglings demanding food. It is an easy job for the adults to pick the aphids from under the leaves to feed the chicks (above). Although many leaves have fallen now, there are still some in the sycamores, peppered with the black spots of, Rhytisma acerinum, the tar spot fungus, and some aphids are still in them. In the last few weeks I have seen Great Tits and Chaffinches feeding on them. Today, I watched a chaffinch hovering under the leaves picking the aphids, a most beautiful sight, which unfortunately couldn't catch on my camera.

Thursday, 7 November 2013

Autumn songs

Despite the days becoming shorter and darker, a few birds are still singing. Robins, both males and females claim their winter territories with their heartfelt, melancholic song, Wrens can be prompted to go on their outburst of song all year round, often by other bird calls and Starlings, donning their brightly spotty winter plumage call enthusiastically from chimneys and aerials.

Wednesday, 6 November 2013

Woodpigeons showing off


Woodpigeons come regularly to my bird table. These two arrived within a couple of minutes. I am not sure if they were a pair, but I doubt it, as they were not happy to be feeding so close. They alternated between feeding peacefully, and facing each other standing high on their tiptoes, chests up, measuring each other up. A bit of wing flapping occasionally - that is how woodpigeons fight, slapping each other with their powerful wings - but mostly just posturing. The photo was capture with my remote control camera.

Saturday, 19 October 2013

Thrushes and whitebeam berries



Whitebeams, a tree related to the rowan, is fruiting now. They have contrasting good and bad years in fruiting (masting trees), and the fruits do not last long, becoming brown and shriveled in about a month from ripening, but berries are large fruits with a lot of pulp compared to the seed content, so they are very rewarding food when available.
Woodpigeons and Crows like the fruit, and so do all thrushes, but they are too large for Robins, Blackcaps and Starlings. They are also eaten (pecked as opposed to eaten whole) or their seeds predated by Blue Tits, Chaffinches and Greenfinches.
 In my local park yesterday, there was a strong contrast between the colour of the fruits of a line of whitebeams. One of them had the brightest red berries, and Woodpigeons and Blackbirds were feeding on it. Note the bulging crop of the Blackbird in the photo above.
 Two trees at the other end of the line had still many unripe berries and as a flock of mixed finches and tits, including goldfinches, chaffinches and great and blue tits descended on it. Suddenly, it became apparent this tree had an owner. A Mistle Thrush started churring vigorously from its centre, while flicking its wings and tail. It seems to make little impact on the little birds, although it kept going for quite a while.
Woodpigeon feeding amongst the berries
Mistle thrush on guard.

And the very nervous one in this short clip.


More information
Snow, B. K., & Snow, D. (2011). Birds and berries. A&C Black. In Google Books.

Tuesday, 15 October 2013

The Crow and the Squirrel

At this time of the year, Grey Squirrels are very busy burying seeds for the long winter. Crows also cache food, and there is an interesting dynamics between both species. Crows are known for eavesdropping on each other, and they avoid caching food if they see other crows around that might steal their food if they know where is stored. But Carrion Crows are good at stealing squirrel food as well. They walk nonchalantly nearby, while the squirrel buries some food, and later they retrieve it and either they eat it or store it somewhere else. Well, the squirrel seems to realise it is just not working for her, and I have often watched how the squirrel goes nuts and starts chasing the crows all over the place (top shot).
Carrion Crow storing food
Crow having a good look at where the squirrel is hiding its food.
These photos are today's, but I managed to get a video of a squirrel chasing the crows last winter.

Goldfinches pecking for grit

I found this flock of Goldfinches pecking the mortar between bricks to get grit. Most bird species that feed on plant materials contain grit in their gizzards. Seed-feeding birds aid digestion by incorporating insoluble grit (silica) into their diets, so that itscours the seed shell and exposed the nutritive inside to digestive enzymes or just helps with grinding the seeds. Soluble grit, containing calcium carbonate (limestone or grit of organic origin) is also actively sought for in preparation for egg laying, as it is a component of egg shells. I guess the mortar has the right type/size of grit for goldfinches, as I have found several photos showing similar behaviour (see here and here). As mortar contains both soluble (lime) and unsoluble (sand) grit, it is unclear which one the goldfinches are obtaining from it.

Wednesday, 2 October 2013

Canada Geese taking off decisions

ResearchBlogging.orgThis morning, the 60 strong flock of Canada Geese that seemed to have roosted in the park were restless. There were continuous loud grunts and honks and, after a crescendo in which more and more individuals joined in the calling, part of the flock took off in a coordinated way. The vocalising geese were making a decision, with individuals deciding to join or not a party leading the departure, maybe to quieter feeding grounds. It is unclear if the individuals felt hungry or if the several dog walkers had made then nervous (or both!).
  Flocking birds have to travel together to stay in a group to search for new feeding or roosting patches, to avoid predation or to migrate. When the individuals differ in their motivations to move away (some might be hungrier than others, for example), there might be a period in which an a consensus is reached about leaving or staying involving communication of the individuals intentions. An individual that is not hungry might change its mind and join in if most of the flock appear willing to move, so as not to become isolated.
  Dennis Raveling, in a paper in 1969, reported on the behaviour before flock taking off in Canada Geese. He observed a large flock in their natural range, in which 77 geese had been marked and radio tracked, including 10 families. Flock departure was preceded by a ceremony, with the neck stretched, there are quick head tossing movements with the bill pointing up and repeatedly, and the white head patch conspicuously displayed - communicating an intention to fly. Geese often spread and flap their wings and start to walk in the intended direction of flight for a few steps (this video illustrate this behavior). Ganders (adult male geese) were more successful at recruiting his family than any other family members, as a shorted time elapsed from his initiation of head-tossing until the family took flight, although all family members initiated head tossing at some point. In a couple of occasions when an excited immature took flight but the rest of the family did not follow, it flew in a circle and returned with the family shortly.
 Other than the cohesive function of the head-toss ceremony for family members, group vocalisations and wing flapping serves to synchronise the whole flock. The coordination of the flock during take off included the presence of an invisible 'starting line': individuals run until they arrived at the same position at which the individual before them had just taken off (instead of taking off where they were). Raveling hypothesized that the contrast between the white tail coverts and the black tail served as a signal to optimise the position of individuals during flight, quite important in such large birds. Families tended to keep together during flight and their vocalisations then changed from grunting to a more trumpet-like honking.

More information

Dennis G. Raveling (1969). Preflight and Flight Behavior of Canada Geese The Auk, 86, 671-681 DOI: 10.2307/4083454

Sunday, 29 September 2013

House Sparrow

House sparrows have now finished moulting and males are donning their more subdued winter attire. The new feathers have buff fringes that tone down their deep chestnut head and black bib. The bill is also yellowish. This one posed for a few seconds on top of a wire fence before flying away.