Sunday, 24 February 2013

Territorial Great Crested Grebes

ResearchBlogging.orgThe breeding season of the Great Crested Grebes is approaching. I have never seen their spectacular courtship so I thought I would pay them a visit in a local park where they breed regularly. I had almost given up on finding them when, from the bridge, I located a winter plumage individual at the far end of the lake. When I got there, I saw that there were two winter plumage individuals, and then an individual with full breeding plumage emerged from the water quite close to me (above). Breeding plumage individuals have a long dark crest and orange and black 'tippets' on the sides on the head, while these are lacking in the winter plumage. I sat down and watched the interactions between the breeding plumage and one of the winter plumage ones. The breeding plumage individual watched the other one, and approached slowly, nonchalantly, occasionally preening its back, or shaking its head, but the winter plumage one appeared to take offence, and swam in the aggressive posture of this species, with head low and stretched forward over the water, and then started to fly, while paddling on the water, towards the breeding plumage one and kept it away. Occasionally it would try to approach diving (see video below). This behaviour went on for quite a while. Both winter plumage individuals appreared tolerant to each other and at some point they stayed close together, so I wonder if I they were displaying early territorial behaviour, and the breeding plumage individual was trying to find a new mate.
 Great Crested Grebes show some variability in their head moult and in February a range of plumages from full winter to full breeding can be seen, so the three individuals were likely adults in different stages of their moult.
Changes in the plumage of the head. The plumage types of individual grebes in relation to date are
given (males = filled and females = open symbols). Dots refer to scores based on examining photographs of grebe-heads, whereas the triangles indicate the results of examining museum-skins. (from Piersma, 1988)

Winter plumage individual on agressive posture,  a few crest feathers and the dark tips of the tippets have already emerged.
 Breeding plumage individual preening its back feathers
It appeared to try and grab the attention from the winter plumage individual, and... very close. 
But it got the wrong sort of attention, as the winter plumage individual threatened it
the summer plumage individual flies away. 
The two winter plumaged individuals close to each other, watched by the breeding plumage one

A couple of short videos on the interactions between the two individuals.

More information
Theunis Piersma (1988). The annual molt cycle of Great Crested Grebes. Ardea, 76, 82-95

Thursday, 21 February 2013

The beak of a grazer

This male Greylag approached me nervously in the park today. It hissed regularly while walking towards me, probably expecting handouts. I crouched down and tried to get a close shot of its beak as it hissed. Geese - and the duck family, Anatidae, in general - have very distinctive beaks with a rounded, 'nail' at the top tip (young Greylags have a black nail) and serrated edges alongside both sides of the upper and lower bill. In the case of the geese, these are quite hard and sharp, remarkably teeth-like (they can draw blood if they get to bite your finger). When looking at the photo I noticed even the tongue has serrated projections. In geese, these help cut grass and plant material when they are grazing. In some ducks these edges have wafer-thin lamellar forming something akin to a whale's baleens, helping them filter out small planktonic organisms from the water.

Wednesday, 20 February 2013

Crow roost at the large poplar

For over 15 years, there has been a Carrion Crow roost at University. In winter, I used to leave work when the crows started to gather on a large poplar tree to spend the night. Each arrival being greeted with raucous calls. I found the atmosphere amazing as their vocal repertoire is so diverse: gurgling, croaking, trumpeting, beak drumming, almost quacking, compounded by the often different tone of voice of different individuals. Tonight, I happened to be by the roost at the right time again. At least 50 crows were already assembled on the top branches, leaving respectful spaces between them, members of pairs closer to each other, and, as I was approaching, pairs and bands of crows flew over me to settle on the tree.
 Crows can fly long distances to roost in their traditional trees (I have read up to 50 miles for American Crow). It can be well past sunset when they settle and they leave first light in the morning. When the nesting season starts, around March, territory holders stop roosting communally, while non breeding birds might carry on sleeping on the traditional roost.
I took this little video of tonights' crow night-time assembly.

Thursday, 7 February 2013

City scavengers

We humans can make a mess. Bins left open or toppled over, the remains of takeaways eaten on the street thrown to the pavement. It is not a pretty sight, but it means extra feeding opportunities for some. Birds take advantage of their surroundings: they eat the berries, buds, and flowers of the trees we plant in our gardens, they do reward our love for them feeding on delicacies on the bird table, but they will also eat our rubbish. Today, a Carrion Crow (top shot) searched for tidbits under a rubbish bag using that lovely crow technique of delicately picking 'things' and moving them aside. They do the same when feeding on leaf litter,  and it is quite different to the energetic, almost full body technique for the same effect used by Blackbirds. The Carrion Crows and Blackbirds often feed at the back of a row of flats, where bins are often left open and bin bags on the ground. My favourite sighting of a scavenging crow was one strutting on a pavement with a large sausage held across its bill, a pity I was driving at the time! Seagulls are supreme city scavengers too, with their bouncy, manoeuvrable flight, Black-headed Gulls are able to avoid the passing traffic - as they will avoid waves out at sea - to deftly dip in the middle of the road to pick items from in between cars.

Snow bonanza for a male blackbird...
...and a female too
Even Robins enjoy takeaway pizza
Black-Headed Gull on the lookout for feeding opportunities

Sunday, 3 February 2013

Sparrowhawk aerobatic displays

Since the start of the year, specially on sunny days, I have had the chance of watching Sparrowhawks displaying. Surprisingly, it is the larger female who takes the lead in these open air flight manoeuvres. They fly high over their territory, flapping their wings in a slow, deliberate way as they climb up, only to dive down, stooping with wings folded back, and repeating the procedure again. Their partner can follow them in their flight path, but often only one individual is visible. This way they advertise ownership of their nesting territory in preparation for the breeding season, although aerial displays are also part of courtship.
This flying in the open behaviour is much unlike the skulking, darting hunting flights of this species, which often just offer a glimpse of the bird. It is when they are displaying that Sparrowhawks - being more visible - are likely to be spotted by Carrion Crows (below) and seagulls and have then to endure being mobbed.

Saturday, 2 February 2013

Mistle thrushes sharing the turf

There is a resident pair of Mistle Thrushes in my local park. The resident male has been singing occasionally since the end of November from a high post on the tallest trees. Mistle Thrushes' song is reminiscent of the Blackbird's but with shorter, more repetitive, mournful phrases that carry quite far. Up to five birds gathered on the grass before Christmas, and when the snow arrived the locals birds had to share the few clear patches of turf under the trees with a flock of immigrant Redwings and a lone Fieldfare in search of earthworms and other invertebrates. Mistle Thrushes are large and bossy, and if the other thrushes get too close, they are chased away without trouble. Resident birds have a head start in the breeding season. They know their patch and as soon as conditions are right they can start nesting right away.
 The male was singing again in the last few days without snow, while the female fed on the grass.
Mistle Thrush and Fieldfare
Mistle Thrush, Redwing (back) and Fieldfare (foreground)
The pair feeding on the snow
Male singing yesterday

Friday, 1 February 2013

Enjoying the sun

After a gloomy, wet winter, the sun made an appearance this morning. This female blackbird did seem to enjoy it as much as me. Sat on a branch, she preened her feathers, fluffed them up and just took the sun in. Blackbirds can display a much more dramatic sunbathing behavior when on the ground. They will spread their tails and wings, fluff their feathers up, open their beaks and flatten their bodies against the ground. They appear to be entranced by the sun warmth, although to the casual observed they might look sick or injured. I have seen Starlings and House Sparrows 'copying' a blackbird doing this on a secluded corner in the local park, like the behaviour was contagious. Pigeons will regularly sunbathe as well.
 Why do birds do it? Hypothesis abound, from synthesizing vitamin D from their oil gland secretions, to antiparasite behaviour. Sunbathing does not necessarily happen on cold or winter days (see example below). For a good article about sunbathing in birds see this post in TetZoo.

Today's blackbird doing some feather maintenance
Another female Blackbird sunbathing in the summer (26/06/2011)...
...and a male in the winter (03/02/2009)