Wing-spreading in Cormorants

The spread-wing posture of cormorants, like the individual above in a local park earlier this month, is one of their most distinctive behaviours. Multiple reasons have been offered to explain this wing-spreading behaviour, is it to dry their plumage? or is it thermoregulation (basking)? Even aiding their balance, signalling successful captures, or help swallowing fish have been put forward as possible explanations for this behaviour. The evidence in the Cormorant overwhelmingly supports the plumage drying hypothesis.
A study by Robin Sellers on wintering cormorants in the river Severn provided strong evidence for wing-drying as the function of this behaviour. Cormorants engage in the open-wing posture almost exclusively after having been diving, when their plumage is wet. After a bout of diving, the cormorant will do some bathing movements in the water, flap its wings and shake its plumage before flying to a perch, where the wing-spreading takes place. Not only the wings, the tail is also spread at the same time. The longer they've been immersed, the longer they will stay open-winged.
Wing-spreading was almost exclusively observed in individuals that had been in water the previous 30 min, and most of the cormorants that had been in the water did engage in wing-spreading shortly afterwards.
Wing-spreading is often followed or preceded by preening the plumage. The duration of the behaviour is also inversely correlated to temperature and wind-speed, supporting the drying hypothesis. Rain tends to inhibit the behaviour.
Wing-spreading in Cormorants is not associated to a successful fishing event, rejecting the 'digestion-aiding' hypothesis.
 Sunny conditions did not trigger wing-spreading, but at low wind speeds cormorants tended to orientate away from the sun.

Super-wettability
So, why don't other diving birds, such as grebes, auks or goosanders engage in this behaviour? The mechanistic, proximate reason is that cormorant feathers are not very water-proof, unlike other diving birds, in fact, they are very become waterlogged after a few minutes in the water. This is not due to a deficiency of their oil glands, but to a different microstructure of their feathers, which is thought to help reduce their buoyancy, and therefore energy requirements, during diving.

Different birds different functions?
Evidence also supports wing drying as the primary reason behind wing-spreading in other studied cormorant species (Shag, Double-crested Cormorant, Galapagos Cormorant, Bank Cormorant and Little Cormorant). However, in the tropical Anhingas, a group related to the cormorant family, wing-spreading takes a much larger proportion of their time than in cormorants, and the behaviour tends to happen for longer in sunny, cool weather, with their back oriented to the sun, and doesn't require wet plumage. Anhingas have a very low metabolic rate, which might favour efficient basking behaviour, and in captive, controlled conditions, oxygen consumption decreased as they engaged in wing-spreading. Therefore, the primary function of the behaviour in anhingas appears to be thermoregulatory ('sunning') rather than drying (although this may also have a secondary role). It is a cautionary tale that apparently identical behaviour in related species can have different functions.

More information
Sellers, R. M. Wing-spreading behaviour of the cormorant Phalacrocorax carbo. Ardea-Wageningen, 83, 27–27 (1995).

Hennemann, W.W. Energetics and Spread-Winged Behavior in Anhingas and Double-Crested Cormorants: The Risks of Generalization. Am. Zool. 28, 845–851 (1988).

Loafing gulls

 Gulls spend a good portion of their days doing what is known as 'loafing', in open areas of good visibility: playing fields, beaches, but also on water and on ice in frozen lakes, the same sites are chosen year on year. These loafing areas are different from night roosting sites. At loafing sites gulls appear relaxed: some sleep - head under wing - others sit or stand watching around, others preen. Immatures may play with objects such as sticks or leaves. Loafing areas are common areas, and tend to be quiet, with little or no squabbling or aggressive behaviour, often with several species mixing in the same area. Individuals come and go, commuting to their feeding areas, unless a disturbance provokes a sudden communal flight. On the coast, the number of individuals in a loafing area follows a tidal cycle - as low tides expose food resources the gulls move away the loafing area to feed- and also time of the year. Tidal influence in sleeping is highly prevalent in wading birds, which strongly depend on exposed shores for feeding. A study in Herring Gulls suggest that they have a dual sleeping pattern, with the proportion of sleeping gulls peaking at midnight and at midday. This may be a common pattern with urban gulls or away from the coast, where food is less related to tidal fluctuations.

A mixed flock of Black-headed gulls, Common Gulls and Herring gulls loafing on a rise on a local park.

Loafing gulls allow good opportunities to check individuals for plastic rings, as shown by this preening Common Gull.

A group of Common Gulls loafing on ice on a frozen pond of (16/1/2013)

More information
Shandelle M. Henson, James L. Hayward, Christina M. Burden, Clara J. Logan and Joseph G. Galusha. 2004. Predicting Dynamics of Aggregate Loafing Behavior in Glaucous-Winged Gulls (Larus glaucescens) at a Washington Colony. Auk 121, 380–390.

Cooke, F. and Ross, R. K. 1972. Diurnal and Seasonal Activities of a Post-Breeding Population of Gulls in Southeastern Ontario. Wilson Bull. 84, 164–172.

Galusha, J. G., JR and Amlaner, C. J., JR. 2008. The effects of diurnal and tidal periodicities in the numbers and activities of Herring Gulls, Larus argentatus, in a colony. Ibis 120, 322–328.

Grey Wagtail feeding

Grey Wagtails breed in upland streams and rivers, but they are common passage and wintering birds in urban waterbodies, from small ponds to lakes. I watched one today in a local park,. Despite their name, they are surprisingly yellow, in the low winter sun this one shone very bright.

Grey Wagtails don't move much away from water, and often feed right at the water's edge picking tiny flies, beetles and other invertebrates, while wagging their long tails up and down. Today I was surprised by the behaviour of this wagtail when feeding on leaf litter by a puddle, as it was energetically lifting leaves and looking under them like a blackbird does.
This clip shows the behaviour:

Greylag nursery

 Many Greylag geese pairs in our large local park have now young goslings. Although geese can be quite intolerant of each other at the start of the breeding season, now the families join together in an area of grass by the lake forming a large nursery. These behaviour might allow them to better detect and defend young from predators. Goslings are precocial and once dry after hatching they can feed by themselves straight away. In the few hours that the goslings spend on their own with their parents they imprint on them and will follow them everywhere. Both parents tend their young by fiercely protecting them from potential predators, hissing or chasing them away, while the goslings feed or rest quite oblivious to their parent's nervousness.
Goslings seek warmth under their mother's wing. Only females are in charge of brooding the goslings in their first few weeks, when they are still unable to regulate their body temperature.
 Despite geese being quite accustomed to people in the park, they still fiercely hiss even as they are being fed. We noticed that pairs differed on how nervous they were. In one of the pairs, the female, instead of hissing, uttered contented calls while she fed and the male didn't hiss at all, despite their goslings being very close to us.

Two families with females brooding young (on the left) and males stand guard.

A group of five goslings follows parents.

Two very nervous parents defending their only young.

Pinkfeet together

At East Park this morning we came across a Greylag flock by the cafe lawns. I spotted the Pinkfoot, and then another, which surprised me. There has been a resident Pink-footed goose in East Park for a year now, a young bird flocking with Greylags. In November, I had spotted a different bird (and blogged about it, see here), also with Greylags at Pearson Park. Could these be these two birds that had got together?
 I looked carefully at my photos and saw that they have distinct bill markings, one with a very small mark close to the nail, the other with a larger U shape mark. The older bird, with the U shape mark (I'll call her Stripe) appears to the the East Park resident. The younger bird, still with tiny body feathers has a small bill patch and matches the bill marks - and tiny white feathers around its bill - of the one that was at Pearson Park. Despite being younger, this bird was bigger and has a larger head, with a Roman profile and a thicker neck and a heavier head, so it might be well a male. Since last saw both birds I was impressed how much more grown up they look. Their neck stripes are better delineated, their head shapes less gentle, and they have a more silvery backs as they have moulted their juvenile feathers. The Pinkfeet stayed near each other in the flock, but one lunged at the other when it got too close. At some point the flock got wary of a radio controlled car, and after a crescendo of cackles, they flew off.

'Dot' Pearson Park 20/11/2014

East Park, today. A male?

'Stripe' East Park 14/2/2014

East Park, today, a female?

Dot's juvenile feathers very noticeable in the flanks, with some adult feathers, darker and silvery just over his legs.

Stripe seems to have a full adult plumage now.

Urban Goosanders

A small group of Goosanders, Mergus merganser, are regular wintering birds in East Park. Not your typical urban bird, you might say, but they can be found in some parks with large lakes during winter, where they may occasionally come for bread (!) (see some great images here). They are stunning ducks indeed, males have black, glossy green heads, with thick, streaked plumage at the back of the head forming a 'bun', and white underside, with a tinge of pink/orange. The tinge in their plumage is caused by carotenoids pigments likely obtained from their diet. Females are grey, with creamy bellies and brown heads with a large fluffy crest at the back. The bill is long and thin, red with a dark hook. They are slim birds and float low on the water, and despite their long necks, they often keep them folded, giving the impression of having large heads.
 Yesterday, we visited the park and initially thought the birds were gone, possibly disturbed by some rowers training in the lake. Finally, we found a pair at the far end of the lake. The male was initially loafing in the shelter of low hanging willow branches near a male Pochard, but then joined the female and started foraging. Despite the urban habitat, they are shy birds, that take shelter near the islands in the lake, and tend to move away from people.
  Goosanders belong to a group called 'sawbills' due to the serrated edge of their bills that help them grip slippery prey, a good feature for a fishing duck. They eat fish, amphibians and aquatic invertebrates, including crustaceans, snails and worms. They rely on transparent water to fish, as they do it by sight, 'snorkelling' like grebes and cormorants do, with their forehead under water before diving propelling themselves only with their large webbed feet. They often probe with their bills on the bottom, to disturb hidden prey. They are also known to engage in communal fishing, where cordons of Goosander will corral fish towards the shallows and dive at unison to catch them.
 This species underwent an expansion during the last century from their Scandinavian range. They only started breeding in the UK at the end of the 19th century and in England since 1941. Now, they breed in upland rivers of Scotland, Wales and Northern England and winter more widely, with the wintering numbers boosted by birds also immigrating from the continent. In the early 1990's, coinciding with population growth in the UK, they started to winter in East Park, often in single figure numbers, with a maximum of about 30. Icy conditions might push them to last remaining open water in lakes, estuaries and sheltered sea shores, although they prefer freshwater.
  Goosanders - in a way similarly to other ducks - are unusual for birds, as males and females have different migration patterns. Most of the Western European drakes, including the British population, migrates to two fjords in northern Norway to moult their flight feathers between June and September, and then return to their wintering grounds in the UK. This male fidelity to their northern moulting grounds might be a cost of the expansion of the Goosander into southern Europe. Females, in contrast, moult later and more locally, late breeding females might moult on their local rivers before their offspring fledges, others congregate in local estuaries with an abundance of fish prey and presence of safe resting areas such as sandbars. It is not known how young birds find the moulting grounds, but association of young birds with more experienced ones in post-breeding roosting sites is a possibility. Pair formation takes place in the wintering grounds, from November-December, in their communal courtship.

The pair of goosanders with Black-headed gulls

Male Goosander 'snorkelling' and showing its 'bun'.

Female about to flap her wings, showing her creamy belly and shaggy 'hair style'.

More information
Hatton, P. L., and Marquiss, M. (2004). The origins of moulting Goosanders on the Eden Estuary. Ringing & Migration, 22, 70-74.

Little, B., and Furness, R. W. (1985). Long‐distance moult migration by British Goosanders Mergus merganser. Ringing and Migration, 6, 77-82.

Coot portrait

This coot called my attention due to the large size of the frontal shield. She came quite close to the shore in a local park and I was able to take her portrait.