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.

Treecreepers and mixed flocks

As 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

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.

Collared dove

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

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 Ornithologica, 46(1), 55-63.

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.