Monday, 8 February 2016

The Mute Swan

I recently purchased The Mute Swan, by Mike Birkhead and Christopher Perrins, after a visit to a local fishing lake where a pair of swans holds territory year round. It has been an interesting, informative read, especially the historical aspects, although I would have liked to read a little bit more on behaviour. Some aspects are dated, for example, lead weights have been banned since 1987, and the mute swans populations have recovered, probably also helped by milder winters (BirdTrends). Mute Swans are the heaviest British birds, with males over 10 kg in weight and 2.20 m wingspan.

There is an unusual colour variety called immutabilis or 'Polish swans' in which the young are white when downy and moult into white feathers, instead of the usual brownish feathers of the juvenile. The feet of the immutabilis form are pinkish grey instead of dark grey or blackish. Read more here.
A normal juvenile with its parents
An immutabilis juvenile (pink bill) with parents.
An immutabilis cygnet (left) with its normal sibling.

Mute Swans get their name from their relative lack of calls, especially in flight, and in stark contrast to their vocal relatives the Trumpeter, Whooper and Bewick. Although relatively quiet, Mute Swans are not mute. They have a repertoire of vocalisations, which, although weak and not carrying long, are quite obvious when at close quarters: they snort, a pig-like call; they hiss loudly like geese, a threat call to predators or people approaching too much, especially when young are about, and they have a short, quiet two note call reminding of rooks'.
A hissing swan
Their wingbeats, however, are loud and make a whistling noise that is audible, it is said, from over a mile. This sound might have replace the flight contact calls of the other swan species.
A pair of Mute Swans in flight.

Non-breeders migrate to safe waters to moult in the summer, often congregating in large numbers. Moulting in breeding pairs is different. They moult when they are breeding: the female moults first, and then the male, once the female's feathers are fully grown. This way, there is always an adult with grown wings, which play an important role in the cygnets defence.
A moulting flock of non-breeding swans at Hornsea Mere

A semi-domestic bird?
At some point in history most if not all adult British swans, and most likely those from other European countries, were pinioned, and therefore, unable to fly. They were a heavily managed species, as it was regularly eaten, and it is likely that this management saved it from extinction from overhunting. The spectacle that is the sight of flying swans would have been much rarer, and restricted to movements involving young birds. In the early XX century, the custom of eating swans disappeared, and, management in most areas was much reduced. In a way, we can see swans as a once domestic, now feral species.

Food and the swan's neck
Swans have a record number of bones (vertebrae) in their necks for a bird: 25. Their long necks allow them to exploit aquatic plants and tubers much deep than other water birds. They use several feeding techniques, shallow feeding in which they keep their neck folded to up-ending, when they use their body and neck to reach deep levels, about a meter deep. They also use their feet in a paddling movement to disturb the bottom sediments and being able to filter out small particles or loosen roots and tubers. Swans might migrate some distances if their territories ice up in the winter.
These feeding swans attracted numbers of coots and various ducks, most likely benefiting of the swans disturbing and pulling deep aquatic plants.
A swan uses its long neck to feed from a hole in the ice

I have never seen the courtship of the mute swan, which appears to have nothing to envy to the Great Crested Grebe's (watch a video here). It involves the pair facing each other with smoothed, dipped wings, and engaging in synchronised, repetitive head dipping and flank rubbing, swimming in circles and, after copulation, both partners paddle and raise their bodies together, with their necks arched and bills pointing down.

Territorial defence
A pair of breeding swans defend their territory, in a lake or river, fiercely: sometimes over the winter if enough food is available and there is no ice. They will chase other swans, with flapping wings being used as a threat, and use a threat display, busking, which I have covered at The Rattling Crow before, in which they swim with strong pushes of both feet together towards intruders, their secondary wing feathers kept high up, neck arched and neck feathers ruffled.
an approaching busking swan.
high intensity busking just before wing flapping and chasing of an intruding juvenile.
Both males and females participate in territory guarding and defence. This pair approached a juvenile busking, chased it away and then swam around the perimeter of their lake.

Nests are often very visible as they are built from surrounding plants, creating a gap in reed beds or river margins. Swans lay 4-7 eggs that only the female incubates while the male keeps guard nearby.
Incubating female swan.
Parental behaviour
Like geese, which are the closest relatives of swans, both parents are involved in caring and defending the young. Adults will carry the young downy cygnets on their backs, often only the cygnet's heads showing over the parents wings, to suitable feeding areas. The male is more involved in territorial and brood defence, often chasing other birds like mallards or coots away. When little, the cygnets are unable to reach aquatic plants at the bottom of the lake, but parents will often disturb the water with their legs, or pull vegetation for the young.
Male swan (cob) chasing a mallard away.
Female with cygnets
Mute swans often swim with one leg, keeping the other dry out of water (cygnet on the left). The cygnet on the right is feeding by up-ending.
Up-ending adult pulling food for cygnet
Normally young disperse in September, once they have grown their first year plumage. Then they leave their parents territory and join a flock of non-breeding birds. However, some young stay with their parents until the spring. The local lake couple seem very tolerant of their young, and they often let them stay until the spring.
Last years first year swan moulting into adult plumage (23/1/15) still in its parents territory.
Non-breeding flocks
Mute Swans do not normally breed until they are 3-4 years old. Young swans unable to secure a breeding territory are more sociable and form non-breeding flocks.

Tuesday, 12 January 2016

Ten cool Northern Fulmar facts

In mid December I visited South Landing, at Flamborough Head. I was pleasantly surprised to find a pair of Fulmars displaying on a chalk cliff ledge, and, when I later mentioned this to a couple of local birdwatchers they replied, 'Yes, they are back', as if it was an expected event for them. This made me realise how little I knew about Fulmars. Back home I started reading about them. I also obtained a copy of 'The Fulmar' by James Fisher, which, aided by an injury that has left me temporarily house-bound, I've been reading and just finished today. This post is a compilation of facts on this fascinating bird.

1. The Fulmar is a superb glider of the open Northern ocean. They brave storms and rough weather when other sea birds might seek refuge in the coast. They use the wind to range over large distances, almost effortlessly. Their flight is quite different to gulls, with stiffer wings. Using the updrafts generated by cliffs, they often wheel tirelessly round and round their breeding sites in a characteristic aerial flight display.
2. The Fulmar is one of just three bird species recorded several times on or near the North Pole. The others being the Snow Bunting and the Black-Legged Kittiwake. In summer, they regularly patrol the Arctic pack ice in the Arctic Ocean pack in search of food. Watch this short clip of a Fulmar sighting near the North Pole.

3. The word fulmar appears first in written language in an Icelandic Saga written about 1200 AD. It has a Norse origin meaning 'foul gull', presumably referring to the oil that they spit out when alarmed and superficial resemblance to gulls. The inhabitants of St Kilda, who spoke Gaelic, also used the word fulmar, while the word was eventually lost in Iceland and replaced by the now used filingur. The fact that the same name was shared between Iceland and the Hebridean island is thought to originate from a time when commerce between Iceland and Scotland was well developed, possibly around the year 1000, in the time of the Vikings, who spoke Old Norse.
Fulmar pair displaying, South Landing 14/12/16.
4. Fulmars return every year to the same nest sites to meet their long-term parter, well ahead of the breeding season, often in December. They greet and bond with each other billing and head bobbing, with much loud cackling calls while keeping their bills open and throat distended. They visit their nest sites on the cliffs on calm days increasingly all through winter until the breeding season. Despite the long-term pair bonds, there is much 'visiting' of neighbours and extra-pair copulation both by males and the females. However, genetic studies show no extra-pair paternity. After mating, Fulmar return to sea before egg laying (the pre-laying 'exodus'), where they presumably store up on reserves for their long incubating period (up to six weeks). Unlike other birds, female fulmars store sperm and the last copulations might take place three weeks before egg laying. They lay a single egg in May, with no replacement if lost, on a bare cliff ledge, or a scrape or rabbit burrow on steep soil slopes. Both parents incubate for about of about six weeks, with changeovers every 4 days. Their superb gliding abilities allow them to range hundreds of miles from the nest site itself in search of food.

5. The oil spitting habit of the fulmar is the defence mechanism of the chick. Fulmar chicks are left on their own from about 2 weeks of age, when they no longer need brooding, while parents travel to get food.  The rapidly fattening chick can by this time defend itself by oil spitting, something that ornithologists trying to ring them have repeatedly experienced. The apparently badly smelling oil, which is a stomach secretion, matts feathers and can cause the death of attackers (large gulls, skuas, falcons) by preventing adequate thermoregulation. The fully grown young, weighing at that time more than its parents (chicks over 1 kg in weight are not rare), eventually fledge in late August or early September and both adults and fledglings move into the ocean. The cliffs become then devoid of fulmars for a couple of months, until their return in the winter.

6. Fulmars are long lived. Adult mortality is low. The longevity record is almost 44 years old, but they are likely to regularly live longer. They mature slowly and breed for the first time at 6-12 years old.  The young birds prospect potential nest sites, often ranging far from their natal sites, and may settle on the cliffs regularly for several years before actual breeding happens. Prospecting birds have been often seen hundreds of miles from the sea in inland crags and cliffs. There are some breeding colonies in quarries miles from the sea.
Northern Giant Petrel in South Georgia photographed by Liam Quinn, CC BY-SA 2.0 via Flickr.

7. The Northern Fulmar's closest relatives are the very similar Antarctic Fulmar and the Giant Petrels, awesome predators and scavengers from the Antarctic. There are two subspecies of the Northern Fulmar, Atlantic and Pacific which some recommend elevating to species status. More distant relatives are other 'tubenoses' like the Storm Petrels and Albatrosses.

8. There are a gradation of colour forms in the Fulmar. One of the extreme forms, the Blue fulmar, which is all slate grey, breeds in the High Arctic and is an occasional visitor of British coasts. The British and Icelandic Fulmar are of the light form, where the body, neck and head are pure white, and the wings and mantle grey.

9. In the last century the Fulmar has colonised large areas of the North Atlantic.  Before 1878, when it first bred in Shetland, the only other breeding colonies were in the small archipelago of St Kilda, off the outer Hebrides (where it has been known to breed at least since much earlier than 1697), Iceland and High Arctic islands. Since then, it has undergone a astonishingly swift range expansion, most likely from an original north Icelandic population, and in the twentieth century colonised most of the cliffs around the UK, Norway, Denmark, and Northern France. The first English Fulmars in recorded history bred in the RSPB Bempton Cliffs nature reserve in 1922.

10. Fulmar feed on small fish, squid, crabs, pelagic molluscs and krill that they hunt from the water surface or in shallow dives, but they are also scavengers. They are rapidly attracted and will feed in numbers on dead, beached or floating whales, and used to come to whales being processed by whaling ships. They will also follow trawlers and feed on offal and fish discards. They will also feed on migrant birds, presumably after then fall into the sea exhausted.  Their scavenging behaviour is most likely aided by their highly developed sense of smell. The fulmars use of whaling and trawling discards, a plentiful food resource was hypothesized by James Fisher to have spurred their range expansion - but recent diet analysis suggest that their reliance on these sources of food might be less than it was thought.

Bonus fact: The inhabitants of St Kilda relied to a large extent in fulmars. They used Fulmars, Gannets and other sea nesting birds for their feathers, eggs, skins, oil and meat. Even fulmar bones were used to fasten their jackets together. The young about to fledge were highly appreciated, and they were were collected the cliffs in mid August, just before they fledged, and when they were at their heaviest. The oil, which solidified when cold into a waxy substance, was collected from the young, poured into Gannet stomachs and stored in small stone buildings with turfed roofs called cletts. Whatever they couldn't use of the birds, they recycled, together with ashes and their own urine to fertilise their fields. Fowling wasn't restricted to St Kilda, it was a traditional way of life in Iceland, Greenland and the Faeroes, but it almost completely stopped when it was made illegal in the late 1930s after an outbreak of psittacosis that affected people processing the birds.

More information

Lockwood, W. B. (1954) Linguistic notes on Fulmar. British Birds 47, 336-339.

Fisher, James (1952) The Fulmar. Collins New Naturalist series, London. 496 pp.

Phillips, R. A. et al. (1999) Diet of the northern fulmar Fulmarus glacialis: reliance on commercial fisheries? Mar. Biol. 135, 159–170.

Kerr, K. C. R. & Dove, C. J. (2013) Delimiting shades of gray: phylogeography of the Northern Fulmar, Fulmarus glacialis. Ecol. Evol. 3, 1915–1930.

van Meurs, R. & Splettstoesser, J. F. (2003) Farthest north polar bear (Ursus maritimus). Arctic 56, 309.

Martin M. (1698) Voyage to St Kilda. London.

Hunter, F. M., Burke, T. & Watts, S. E. (1992) Frequent copulation as a method of paternity assurance in the northern fulmar. Anim. Behav. 44, 149–156.

Friday, 1 January 2016

The variable Redpoll

Redpolls are small finches with a tiny bill, a crimson spot on the forehead and a little black bib and mask giving them slanted-looking eyes. Their plumage is so dense that on their faces it can partially hide their bill, giving them a flat face. They are found from the Arctic (where they are resident), to subarctic and temperate open forest and scrub and specialise on small seeds, mainly from birch, but also alder, willow, spruce, larch (above) and pine cones. They will also feed on various wildflower seeds near the ground.
 Redpolls are very entertaining to watch as they feed, as they reach catkins and cones using acrobatic, agile movements, reminiscent of tits. In addition, they can use one foot to hold onto a stem, a bunch of seeds or catkin to reach the seeds more easily, like goldfinches. They can apparently store up to 2 g of seeds in a expandable pouch in their throat, to eat later in less exposed conditions. Redpolls have been seen 'bathing' and burrowing tunnels in the snow. These tunnels have unclear function, as they don't appear to use them to shelter from low temperatures, rather, they appear to fulfill a social role, or just be a form of play.
  Redpoll flocks have erratic, nomadic, movements in winter in search of seeds, often travelling in the company of Siskins. They also have 'irruption years', following failures on the seed crops on which they rely, or high population densities after a good crop year, often spurred by cold weather. One of the largest irruption years were in the winter of 1995-96, where Arctic and Common Redpolls arrived in the UK in good numbers.
 The taxonomy of Redpolls has been very fluid, with three species, Arctic, Common and Lesser -each with various described geographic subspecies- recognised, but at some point six were described. The browner, small and very streaked 'Lesser Redpoll' breeds in the UK. Diagnosis was based on the lightness and amount of streaking in the plumage and also bill shape and size and overall size. However identification is often difficult, as there is a lot of variation, and many individuals would fall in between the 'classic' species descriptions, resulting 'in much collective head-scratching' in the words of Riddington and colleagues.
  A recent study by Nicholas Mason and Scott Taylor from Cornell University, sampled 77 Redpolls from around their distribution range and looked at the diversity across their genomes, niche differentiation, morphological diversity and gene expression patterns. Surprisingly, all Redpolls were extremely similar genetically, with barely any genomic differentiation between 'species'. The different colour patterns and bill shape can be explained by different gene expression patterns (e.g in response to temperature), but the authors did not find a clear-cut morphological differentiation between species, as many individuals were intermediate. Although recent adaptation to particular local conditions, for example the dominant available seeds) might have happened, it is likely that the nomadic migratory movements of Redpolls result in a lot of dispersal and gene flow between populations and incipient regional varieties, preventing differentiation and subsequent speciation. Perhaps we should just enjoy Redpolls as a delightful bird on its own, and worry less about tidying individuals away into imaginary boxes.

More information
The Cornell Lab of Ornithology Cool Redpoll Facts.

Riddington, R., Votier, S. C., & Steele, J. (2000). The influx of redpolls into Western Europe, 1995/96. British Birds, 93: 59-67. Pdf here.

Gustave Axelson (2015) From Many, One: How Many Species Of Redpolls Are There? Commentary on Mason and Taylor paper on the The Cornell Lab of Ornithology blog.

Mason, N.A. and Taylor, S.A., 2015. Differentially expressed genes match bill morphology and plumage despite largely undifferentiated genomes in a Holarctic songbird. Molecular ecology, 24: 3009–3025. Here.

Collins, J. E., & Peterson, J. M. (2003). Snow burrowing by Common Redpolls (Carduelis flammea). The Kingbird, 53, 13-22. Here.

A male Redpoll feeding on Alder catkins
A Redpoll feeding on Rosebay Willowherb.

A male Redpoll on Alder
An individual on Alder, illustrating their ability to hang upside down from thin branches.

Monday, 21 December 2015

Goldfinch Chorus

This morning, while I walked around the park I heard a distant loud cheerful chatter. As I approached I realised there was a flock of Goldfinches up a large horse chestnut and many of them were singing. It is the second time this week that I witness this behaviour, the first time it also happened in the morning, the flock of Goldfinches singing together from a bare sycamore. Some seemed to amuse themselves pecking the branches, but in general they were just calling and singing. Goldfinches are very social birds, they often nest in loose colonies, and, although individuals might squabble for a particular food source, they often feed together in flocks. Whereas in the summer they like the seeds of teasels, thistles and other herbaceous plants (even lavender seeds!), in the winter, they can often be seen feeding on trees, like Alder, Plane, Ash and Birch. I haven't managed to find much information about chorus singing in Goldfinches, but the behaviour has been described in the closely related American Goldfinch and Siskin, where the males in the flock joining in chorus song in winter and spring.
Goldfinch flock singing (two bulkier Greenfinches are amongst them)

Sunday, 13 December 2015

Pair of Moorhens

There are now two Moorhen pairs in the park. They own each one end of the pond, a pair owns the island and the other the 'rock' with a couple of clumps of marginal plants. Today the island pair was very cosy, both individuals together, the one on the left preening around the neck of its partner. Moorhen males are slightly larger and heavier than females, so the larger individual on the left is likely to be the male. The Coot pair abandoned the park after their two failed breeding attempts on the stolen Moorhen nest.

Thursday, 3 December 2015

December songsters

It is not unusual to hear bird song in December. Robins and Goldfinches sing year round, Wrens will burst into song at any time. Do Starlings ever stop singing? I don't think they do.  Collared Doves and Stock Doves, after a short rest at the end of their breeding season, can now be heard calling again.
 In sunny winter days, Song Thrushes will start singing, maybe more towards January.
Wren in full song in October
Collared dove singing a couple of days ago.
Starling singing yesterday
 Today I heard two bird species singing, however, which I've never heard singing at this time of year. This morning I heard distant fluting phrases that sounded like a Mistle Thrush. I went to investigate and there it was, a Mistle Thrust atop a tree, singing contentedly.

 Blackbirds, normally will sub-sing in the winter. This is an eery, very quiet song, that usually subadult individuals carry out, as if 'practising' singing, well hidden in bushes. But as I was leaving work today, as it happened last week, I heard the surreal full song of a blackbird, its beautiful notes raising over the cacophony of the Carrion Crow roost at campus, and transporting me into spring. I had to check this out. There it was a full adult male Blackbird was singing from a wall. Given that it was quite dark at 16:15, the photo on top was the best I could manage without using the flash, but I recorded a short video of it. A very very unusual thing to happen in early December. I wonder if the unseasonally mild weather we are having is confusing this normally spring songster.

Tuesday, 9 June 2015

Fledgling crow

As I took the kids to school this morning, I noticed a couple of crows on the grass on the school grounds. One of them was hunched up and I thought it looked like a young one. As I was leaving I went to check. Still looking like it would be more comfortable sitting in its cosy nest, it looked curious as I approached, and it didn't flee. It's first encounter with a camera, taking things in. As human babies, Carrion Crows young ones have dark blue eyes, which will darken to rich brown as adults. The blue eyes, pink mouth and brownish feathers help tell young from adults, but the general attitude is different too, as young crows tend to be much tamer than the adults.