Thursday, 27 February 2014

Honking Carrion Crow territory owners

My working morning has been enlivened by a pair of Carrion Crows advertising their territory ownership repeatedly from atop the building opposite my office. They use a peculiar call for this, which has a a honking horn quality, drawn out and without the 'r' sound present in many crow calls. It carries far, and is made while the bird carries out a self-advertising display, by bending forward exaggeratedly, with the tail fanned and, as they make the call they stretch forward and back on a graceful curve. I photographed the pair yesterday nearby (above), with one of them doing the advertising call. This is the call from a Xenocanto recording by Matthias Feuersenger.
More Carrion Crow calls from the blog 'Echoes from Nature" here.

Monday, 24 February 2014

The bill of the blackbird

ResearchBlogging.orgThis morning I spotted this male blackbird sitting in a bush. It had the brightest orange-pink bill I have ever seen in a blackbird, and it prompted me to finish writing this post that had been for a little while in my drafts folder.
Carotenoids are pigments obtained from the diet in animals that give yellow to red hues to many sexually selected ornaments. Carotenoids are antioxidants and have a role in the immune system and if they are supplemented in the diet they often increase the condition, growth and survivals of organisms, therefore, their use as honest signals of body condition in a sexually selected context is one of their most studied roles: Females may assess male quality by using signals, if they are good indicators of the male body condition.
 Blackbirds are sexually dimorphic: males have a black plumage and orange bill and eye ring, while females are brown and their bills are brown or have a pale yellow base. There is intrapopulation variation in bill colour. Young males often have black streaks or a black bill in their first winter and adult bills range from yellow to bright orange. Several studies have investigated the role of sexual selection in bill colour variation. Results show that male blackbirds with orange bills are heavier and larger, have less blood parasites and pair with females in better condition than males with yellow bills. Females in good condition start breeding earlier and make more breeding attempts during the breeding season, which correlates with the number of fledglings produced per year. The correlation between female condition and her partners bill colour appears not to be due to direct female mate choice, that is, as no preference in females for more orange bills has been found in two studies. It is possible that this correlation is due to males with brighter bills being able to secure better territories during male-male conflict, and the female choice happens on territory quality. Although blackbirds are socially monogamous and form long-term pair bonds, there is a certain amount of extra-pair copulations and it is not known if polymorphism in bill colour determines how many extra-pair copulations can males achieve.
 It is surprising how much there is to learn from such a common bird.
Here are some photographic examples of bill colour polymorphism in male blackbirds.
A young male subsinging (31/Jan/2010)
Another young male with brighter bill but streaks of black (18/Jan/2014)
An adult with bright orange bill
An adult male with yellow bill.
More information
  B. Faivre, M. Preuault, M. Theury, J. Secondi, B. Patris & F. Ceuzilly (2001). Breeding strategy and morphological characters in an urban population of blackbirds, Turdus merula Animal Behaviour, 61, 969-974 DOI: 10.1006/anbe.2000.1669

Bright A, Waas JR, King CM, & Cuming PD (2004). Bill colour and correlates of male quality in blackbirds: an analysis using canonical ordination. Behavioural processes, 65 (2), 123-32 PMID: 15222961

Monday, 17 February 2014

Swinging goldfinch

A trio of goldfinches came to the feeders today. One of them, while it waited on nearby branch to feed, carried out a curious 'dance', repeatedly swinging its body from one side to the other while it called. I looked into this and found out the dance it's got a name: 'pivoting display'. In a courtship context, the display is carried out by the male and he swivels towards and away the female as he swings. The wings are somewhat lowered - which makes the golden bars more visible - and the tail spread, showing the white patches. Female also pivots, and when both sexes carry out the display it may end in copulation.
 The pivoting display is also used in aggressive contexts, and maybe the goldfinch was becoming impatient waiting by the feeder. I shall keep an eye on my visiting goldfinches and see if I can record this behaviour. I found a little video showing the behaviour in a charm of goldfinches. Check the individual at the bottom of the image from s 36.

And a great video of a pair of captive goldfinches courting.

Sunday, 16 February 2014

Singing Great Tit

This Great Tit was singing enthusiastically from a tree today. I whistled its 'tea-cher' song and, curious, it came out more in the open, showing its black chest band, head high.

House Sparrow chirping

Male House Sparrows still have greyish fringes on the the feathers of their their bibs and heads, so they are still not looking their best. They are starting to become more active though, chirping from the inside of bushes. This one was right inside a rose bush, but somehow I manage to get a clear field of view and take some close ups while it chirped.

Displaying goosanders

There were three pairs of Goosanders in the park today and I spent some time watching them, as they were much more active than a few weeks back. The males displayed in front of the females, stretching their necks with their head feathers erect, and fast-forwarding on the water, at the same time making a string of water droplets that fell in front of the females (above). The females would stretch out of the water and flap their wings or lunge at other pairs.
Note how flat the top of the head of the male is compared to the top photo.
Stretch and flap.
Nicely paired up.
This female threatened another one.

Thursday, 13 February 2014

Stock dove

In the calm after the storm, Stock Doves resumed their activities in the park. This morning there is a lot of chasing and singing going on around the trees where they nest. This individual sat sunbathing and preening itself.

Sunday, 9 February 2014

Male Blackbird courtship display

The Blackbird must be one of the birds I am most familiar with. Yet, I have only watched it courting once previously, and have never witnessed a copulation. Today I watched a male apparently subsinging inside a bush, but, upon approach, I realised it was an adult male adopting a strange, stretched-neck posture. I watched the bird and realised that there was a female low inside the bush. I couldn't include her in the photos, but I managed to get a few of the male. The one above is my favourite, there are a few more below.
 This is David Snow's description of the blackbird's courtship display:
The fully developed courtship behaviour of the male is the blackbird's most striking display. The head, with the crown feathers partially erected and the beak open, is stretched forward; the neck-feathers are compressed, and the body feathers fluffed out, especially the feathers of the rump, which form a conspicuous hump; and the tail is fanned and depressed. The displying bird has a curiously wild, staring appearence.[...] The whole time, with his beak held open, he usually utters a low 'strangled' song, made up of chattering alarm notes, rough warbles and subdued snatches of what sounds like true song.  If the display is performed in a tree, the male remains stationary or at most occasionally shifts to another perch near by, while the bowing part of the display is more prominent, developing into a rhythmic up and down movement of the whole head and neck.  
This display takes its full form during pair formation, unpaired males - young males or widowers - court females most often in February-March. Paired females attack displaying males, unpaired females appeared indifferent, although they might later mate with the male.
A brief form of the display occurs just after females solicit copulation in the days prior egg laying. According to David Snow, copulation is always interfered with by other males, who jump at the copulating male, often knocking him off the female.
This is the first photo I managed of the blackbird singing

More information
Snow, D.W. 1958. A study of blackbirds. George Allen and Unwin Ltd.

Friday, 7 February 2014

The scary bright eyes of the Jackdaw

ResearchBlogging.orgJackdaws breed in loose colonies, and unusually for corvids, in cavities in trees, cliffs or buildings. There is often very strong competition for nest sites, and the pair will defend their nest fiercely against conspecifics. Jackdaws are also unusual for having very contrasting, almost white irides. In a recent paper, Gabrielle Davidson and her colleagues from Cambridge and Exeter Universities tested the hypothesis that the bright, contrasting eyes of the Jackdaw serve as a strong warning signal when adults are occupying a nest, warning intruders not to come in.
 They set up 80 identical nest boxes in woodland areas in Madingley (Cambridgeshire) during the pre-breeding season (February-April), when Jackdaws prospect potential breeding sites. The nest boxes had two perches, one at the base and the other just by the entrance. They fitted the inside of the entrances of the nest boxes with a circular printout, visible from the outside. Each nest box was randomly assigned one of four types of printout: a dark circle (control) a dark circle with white 'eyes'  of the same dimensions of a Jackdaw (eyes only), a printout of a face-on photo of a Jackdaw with eyes retouched to increase the brightness (bright eyes), and the same printout but with dark eyes (dark eyes). They used remote video cameras to record Jackdaw visits to the nests, and the time they spent sitting on the nest itself and the perches.
 The results were striking. Jackdaws alighted on the nest box significantly less when the bright eye print was in the nest entrance. In addition, they spent very little proportion of their visit time on the perch closest to the entrance both in the eye only and bright eye treatments. The visiting Jackdaws actually entered the nest box in two occasions, one in the control and another one in the dark eye treatment.

This experiment shows that eye colour can be important in communication with conspeficics. The pale eyes are a warning signal to prospecting Jackdaws that a nest is occupied, and they avoid approaching the nest entrance once they are on the nest box. This reaction to an occupied nest reduces intraspecific conflict, as it might save them from a fight and potential injury. Davidson et al speculate that the 'eye fear' response of Jackdaws might be more general, and they might react in the same way to sparrowhawk eyes, for example, as it is known that they are sensitive even to eye gaze in humans - they will delay their approach to food if a human is looking at them.

More information
Davidson GL, Clayton NS, & Thornton A (2014). Salient eyes deter conspecific nest intruders in wild jackdaws (Corvus monedula). Biology letters, 10 (2) PMID: 24501271

Tuesday, 4 February 2014

Jackdaws inspecting potential nest site

A bright blue sky greeted us today. Days are getting longer and there is a certain spring feeling in the air. Jackdaws are not common birds in my local area, but there are a few, loyal to their territories, and usually nesting inside chimney pots. Today, I spotted a pair sunbathing on a tree, next to each other. After a while, they flew to a chimney and one of them - likely the male - inspected each of the chimney pots carefully, while the female sat around. Then he called and fluffed up its plumage and both flew to the other side of the street, meeting another pair. A Carrion Crow then landed on a aerial close to the chimney, came down and checked inside the chimney pots the Jackdaws had been inspecting. It looks like crows watch carefully what other animals are doing and like to check just in case there might be something in for them. In the case of nesting Jackdaws, the adults will rarely leave the nest unattended once there are eggs or chicks in it, as predation is the main cause of nesting failure.
 It is early for Jackdaws to start nest building, but their instincts are definitely stirring.
Hole number one, check
Hole number two, check
Hole number three, check

The individual on the left (prob the male), makes some soft calls with plumage fluffed up
The curious Carrion Crow watching the Jackdaws

More information
Coombs, F. (1978). The Crows: a study of the Corvids of Europe 255 p. London: Batsford.