Thursday, 19 April 2018

Gulls mobbing Buzzard

From my office I hear several Herring Gulls start calling plaintively, kyeoh! kyeoh! a loud, far carrying call that I associate to buzzards overhead. I looked through the window. The local Carrion Crows had assembled atop a large poplar, watching nervously, calling and displaying wing shuffling and tail fanning.
A dozen gulls soared and called - all the local Herring gulls - slowly assembling and ascending on the thermals. Then I see a Buzzard, soaring higher. The gulls didn't reach the buzzard's height and it eventually drifted away and the gull calls died off.
 Gulls often alert me to raptors. A couple of years back it was a Honey Buzzard, migrating over town. I pay a lot of attention to the gulls alarm call since then!
 Later, at home, the scene appears to repeat itself. Alarm calling gulls. I grab the camera and go out into the garden. Two Lesser Black-backed gulls are mobbing a Buzzard.
 This gull alarm call is persistent and sounds distressed, it is hard to ignore. It seems to attract other gulls too, who soar and chase the potential predator. I wonder if it is how young gulls learn to identify the predators they are likely to come across in their lives. Crowd knowledge of the enemies, initiated by older gulls with previous experience, who in turn learned it in their youth. Immature offspring of the gulls initiating the mobbing are likely to be around. The adults could be 'teaching' young about potential predators and the young are likely to benefit from this at some point in the future. This is a hypothesis called 'cultural transmission of mobbing' which was explored in some experiments by E. Curio and collaborators in 1978. They showed that exposure of a novel object to a 'naive' Blackbird at the same time a 'teacher' blackbird is mobbing results in learning to mob the new object (in one of their experiments a colourful bottle). This teaching could be passed through six rounds of learning in which the learner becomes the teacher of a new bird, and so on. The fact that enemies often have to be recognised culturally was put to a sad test when captive reared endangered Hawaii crows (or Alalā) were released into their natural habitat. The last wild Alalā had died in 2002. Two of six newly released birds were predated by native hawks, to which the captive reared birds were completely naive in the first week after release. The conservationist recaptured the surviving birds and started an intensive 'predator training' program in which the captive crows were exposed to hawks calls, hawks flying overhead and simulated hawk attacks. Hopefully the savvy crows will do better when they are released next.
This time of the year there seem to be a passage of migrating or dispersing Buzzards over the city. The gulls are breeding, probably incubating now, and a buzzard could be a predator likely not for them, but for eggs left unattended or young chicks. It makes sense that the gulls see off the potential predator.
I got this short clip from the garden:

More information
Curio, E., Ernst, U. and Vieth, W. Cultural transmission of enemy recognition: one function of mobbing. Science 202, 899–901 (1978).

Different gull calls: here.

A blog post including some great photos of Herring gulls mobbing a Buzzard

Sunday, 28 January 2018

Mute Swans drying and tucking foot

Mute swans often stick one foot in the air as they swim (top shot) easily steering themselves with the other foot. I had often wondered what the purpose of this habit was.
  The two Mute Swans in my local park have afforded close observation in the last couple of months. Last week I noticed that sometimes they have one of their legs tucked under their flank feathers, virtually invisible, only a bit of the 'knee' showing, while swimming with the other leg. This behaviour probably results in keeping one leg quite warm under the plumage.
Yesterday I put both behaviours together by watching how the young swan took one foot out of the water, shook it and left it out for a while. Then it behaved like it wanted its leg dry before tucking it under its feathers: it tucked his leg under the feathers, but seemed not to be happy about it and it stuck it out again and shook it a bit more before finally tucking it in for good.
 I had noticed that cygnets, even before they have feathers, have this habit of tucking a leg out of the water over their body. I just had never realised the adults would do it too, preceded by the leg-stuck-out while drying.
This behaviour has also been reported in other swan species and although thermoregulation seems to be the underlying reason, both cooling and drying/warming have been proposed as explanations for the behaviour.
 The next series of photos illustrates the sequence of behaviour.

The following photo is from 21 June of 2015, taken in a local fishing lake. A young downy cygnet a few weeks old. You can notice how its right leg is tucked by its body, outside of the water, while it preens. When it grows feathers, the same position results in a leg completely covered with feathers.

More information
Why do some swans only paddle with one leg, with the other leg tucked up under the wing?

The Whooper Swan. Here. p 93-94.

Thursday, 25 January 2018

The first singing chaffinch

The first chaffinch sung in the park today. They often start tentatively, but this one sung three or four times before starting foraging on the tree. Spring must be in the air!

Wednesday, 13 December 2017

Singing starlings

Starlings sing all year round. True that in spring they spend more time atop vantage points near their nest, throat feathers fluffed, wings fluttering, emphasising their phrases, but even in December they find time to sing. They include calls from other birds, often copied to perfection: pied wagtails, sparrows, swift as some of the ones they have misled me when I realised it was a starling singing. I was tidying up the photos of the year when I found this photo from May, which captures the enthusiasm of a starling singing.

Saturday, 18 November 2017

Ringed Common Gull

The Common Gulls at the local park have been back for a few weeks, slowly building up in numbers to about a hundred today. I searched for ringed ones and found JV47, which I first saw on its first winter in January 2015. It is a fully adult gull now and trusting enough to allow me to take a close up.
Another shot from today.
JV47 as a 1st winter immature in typical chick 'hunchback' posture (23/1/2015). He was ringed  the previous October at Bergen, Norway.
Click here to find out about other ringed common gulls at Pearson Park. If you find a ringed gull and you can read the ring, you can report it to Euring, the European Ringing scheme.

Wednesday, 15 November 2017

Allopreening moorhens

I have only once before seen Moorhens allopreening, and I could not photograph the behaviour. This morning I was luckier. I saw the pair of Moorhens on the other side of the lake in my local park next to each other. One of them adopted the a posture reminiscent to the 'invitation to mate posture', although standing, with head tucked under the chest. The other moorhen then started preening its head and neck, while the first moorhen relaxed the posture. The preening moorhen then adopted the invitation position and the second one briefly preened it. The bouts of preening were not very intense, but directly followed the specific head under chest posture.

This clip shows how the moorhens take quick turns soliciting the preening, and how the preening itself appears rushed and rough at times one pulls the other's feathers.

Thursday, 9 November 2017

A story of ringed Mute Swans

Last Wednesday 1st of November I went to Pickering Park. There were six Mute Swans. The resident cob (841 yellow ring), followed by the resident pen (ringed 842, top shot) was busy busking towards a white swan in the lake, who tried to avoid him and ended up preening on the bank at one end. It was a polish variant one, possibly a young of last spring, and when it came out to the shore I could see it was also ringed (red 182Y).
There were also three brown-feathered young swans, starting to moult into adult plumage. Just one of them was ringed (red 537). I assumed they were offspring of the resident pair. One of the brown young kept near the polish one being chased, joining it on the shore.
182Y at Pickering on the 1st of November.
The brown swan accompanying 182Y at Pickering.
The resident pen at Pickering.


On Sunday 5th I went to Pearson Park. I was pleasantly surprised to find a mute swan, brown, not ringed. After a while I realised that there was another mute swan, white, on the other side of the pond. The small lake at Pearson Park has very rarely held swans, and not for too long. The last one I saw there was a juvenile from November 2005 to March 2006, when another two appeared in the park before all departed. I casually checked for rings, as I often do, and after some trying I managed to read it. I was surprised to find that the white one was the same that was being chased at Pickering Park, 182Y! The brown young wasn't ringed, but its plumage development is consistent with the one keeping near 182Y at Pickering, so both birds must have left the lake together, possibly an incipient young couple? 
182Y now at Pearson Park. I was able to read the ring as the swan swam.
The brown unringed young at Pearson park.
Both swans at Pearson Park. The white swan showed some aggressiveness towards the brown one, pecking it when it got close.
The swans are getting a lot of attention at Pearson Park. I think the brown one is a male, as it occasionally fluffs up its neck which looks thick in comparison to the other. Still there today, being fed by locals. There is currently a good empty breeding territory at Oak Road lake, it would be good if these two moved there!