Wednesday, 18 January 2017

A wintering Chiffchaff

Warblers are generally migrant birds and we tend to associate them with warm weather and their songs heralding spring as males settle territories. One of the exceptions is the Blackcap, which I have covered before in the blog, which in the last half a century, has become a regular winter warbler in the UK, with some birds breeding in Germany migrating west to the UK, where they enjoy the food provided in garden feeders and milder temperatures. The other is the Chiffchaff is also a wintering warbler. Although not common, it winters around the coast and estuaries, especially in the South, and also industrial or sewage treatment sites where warm water encourages insects. In contrast to the Blackcap, The Chiffchaff is fully insectivorous through the winter so it doesn't benefit from berries or garden feeders. In the first day of the year I spotted a small bird in the garden and thought it would be a Goldcrest. Its relatively sedated moves (for a Goldcrest!) prompted me to look harder and I saw it was a Chiffchaff. A couple of days ago the bird, presumably the same one, was back I managed the top shot through glass, as it fed on the apple tree, where I've seen it several times. Some of the apple tree branches have an infestation of Woolly Apple Aphids, and this appears to be what the Chiffchaff is eating (you can see some fluffy colonies under the branch that the bird is sitting, to the left).

Friday, 13 January 2017

A lucky front shot of a male Mute Swan on a local park. He was with his polish variety partner, and ringed and approached me as I walked around the lake.

Sunday, 11 December 2016

Standing pretty

In the low winter sun, this magpie was tree-topping, displaying her contrasting black and white plumage, a typical territory-owner behaviour. They will 'tree-top' on aerials and buildings alike in towns. This one also regularly 'tail-flirted': a quick bow and tail flick, which is very noticeable and draws attention. Magpie's apparently black plumage has structural iridescent colours, blue sheen in the wings and green and purple in the tail tip - as shown in this tail feather - which are shown during displays and aggressive encounters. Breeding, territory-owner magpies have the brighter and greener iridescent hues than non-breeders. Plumage brightness in birds especially in body parts that are displayed during territory defence or during fights, reflects the owner's health and attractiveness, so their display advertises not only territory ownership, but its good body condition, so that potential challengers can assess it, and potentially avoid fights that they might be likely to lose.

Wednesday, 7 December 2016

On Magpie marriages

As in other corvids, like Ravens and Carrion Crows, non-breeding magpies flock together. The non-breeders tend to be young birds, while territory holders, which breed, are more likely to be older. There is a hierarchy in the flock, and the dominant birds are more likely to be the next in line in obtaining a territory. Magpies form pairs in the non-breeding flock.
This morning, I witnessed my second ever 'great Magpie marriage', one or the most puzzling Magpie behaviours. A group of seven magpies (top shot) were high on a tree, calling, a short call, 'chak!' and bowing with wings half spread, displaying, pecking the branches, or chasing around the tree, but mostly watching each other.
This is a short clip of the gathering.

This behaviour, which usually takes place in the winter, in sunny mornings (although it was quite dark and cloudy today) was traditionally interpreted as the way Magpies form pairs before nest building starts. Tim Birkhead, in an article for British Birds, quotes this passage from Darwin's book 'The Descent of Man':

The common magpie (Corvus pica, Linn,), as I have been informed by the Rev. W. Darwin Fox, used to assemble from all parts of Delamere Forest, in order to celebrate the "great magpie marriage." [...] They then had the habit of assembling very early in the spring at particular spots, where they could be seen in flocks, chattering, sometimes fighting, bustling and flying about the trees. The whole affair was evidently considered by the birds as one of the highest importance. Shortly after the meeting they all separated, and were then observed by Mr. Fox and others to be paired for the season.

Birkhead's research with the Magpie population of Rivelin's Valley in Sheffield showed that instead of a pair formation congregation, this behaviour, is instead a territorial challenge by the dominant non-breeding pair. The rest of the flock attend to witness the event and, although the territory owners often keep their territory, in some cases they are ousted by the dominant non-breeders.

My first Magpie marriage, on a sunny morning a few years back (9/11/09). Individuals fluffed their white feathers in their displays.

More information
Birkhead, T. R. Studies of West Palearctic birds: Magpie 189. British Birds (1989). 82:583-600. Here.

Birkhead, T.R. 1991. The Magpies. The ecology and behaviour of Black-billed and Yellow-billed Magpies. T&AD Poyser, 270 pp.

Thursday, 17 November 2016

Playing herring gulls

This morning at a local park, I noticed a young Herring Gull picking an object, flying off and being chased by another. Then the gull landed on the water and dropped the object and pretended to dive to pick it up repeatedly, as in a lazy drop-catch game. When I saw the object at a better angle I realised it was an empty freshwater mussel shell, which happened to float. Funnily enough, a couple of hours later when I walked past either another or the same young Herring Gull was still playing with it.

The young gull flies off with the freshwater mussel shell.

Later on, with cloudy weather, two gulls handling the shell.

Wednesday, 16 November 2016

The bristle head crows

Carrion Crows have a complex social structure. Territory-owning Carrion Crows remain paired year round, often flying and feeding together or not far from one another. They remain near their nest during the breeding season, although they may range wider outside this period. Birds that don't hold a territory form part of a loose flock that roosts communally, usually in large trees. Both male and female of a pair participate in territory defence, keeping other crows (or potential predators) away from the nest. Males have a more prominent role: if a male loses his mate he is able to defend the territory until he remates, but a female losing his mate will also lose her territory, as she would rapidly be evicted by other pair.
In one of my local parks there is a very high density of Crows. There are several territories, but the park is also the main ranging area of the non-breeding flock (where there is also a winter roost). There are a lot of interactions going on, but without ringed birds, it is hard to make sense of what is actually happening. Yesterday, I observed several interesting interactions. First, a Black-headed gull appeared most annoyed with a Carrion Crow and mobbed it repeatedly, dive-bombing on it when the crow tried to stop on an aerial. The crow did not vocalise and deftly avoided the gull attacks. Later, I heard the rattling call of a crow and watched a chase between two crows, one of them calling with the call I usually associate to mobbing a raptor. Crows, it appears, can use this vocalisation to fend off conspecifics.
 Finally, I watched a Crow it an amazing display: its head feathers raised, bill pointing down, looking really at its best. After taking a few photos, I realised it's partner was walking nearby using the same posture. Today I learned about this display in 'The Crows' by Franklin Coombs. It is called the 'Bristle head' display. It is a territory-owner display, used in territory boundaries to signal their occupancy, and also aimed at intruders within the territory. Both members of the pair display while they walk about. There is no vocalisation. Territory intrusions mostly occur during the spring, but there is also a peak in October-November.
 I can only presume that this pair of crows are a pair ot territory owning breeders. They do look in great shape!
This is a still from a video, which shows both members of the pair with their 'bristle heads'.
A side view of the displaying crow. 
This photo is a bit overexposed, but it shows the details and metallic iridescence of the crow really well.

Wednesday, 9 November 2016

Chok, chock, chock!

I've been wanting to take a photo of a Blackbird in this posture for a long time. Blackbirds do often cock their tails. When they alight they do that tail-cocking so as to keep their balance - in a similar way to Woodpigeons - they often do a jerky tail-cocking action when they do one of their various alarm calls 'chok, chok, chok' at the same time than they flap their wings. On Sunday, a windy day, this Blackbird perched on the side of a drinking trough, the wind made it lose its balance a bit and it stayed, tail cocked, for that second longer for me to press the shutter. Got you!