22/03/2011
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Shore Lark – a lark of all trades

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Shore Lark by Steve Young (www.birdsonfilm.com).
Shore Lark by Steve Young (www.birdsonfilm.com).

While many British passerines are sunning themselves in tropical Africa, winter heralds the arrival of several distinctive and sparsely distributed songbirds, among them Shore Lark. However, the presence of small parties of this species on an east coast saltmarsh may be becoming a thing of the past.

Though still present in small numbers most winters, the species’ British decline is mirrored in its Scandinavian home territories, possibly due to changes in farming practices. This loss is made more melancholic by the realisation that the species is actually one of our more intriguing winter migrants, warranting a good deal more attention from birders, ornithologists and conservationists.

Shore Lark by Markus Varesvuo
This Shore Lark might have moved south if the snowy conditions persisted, perhaps joining the small parties seen annually on the east coast of Britain. Photo by Markus Varesvuo (www.birdphoto.nl).

Up with the lark

Shore Lark is possibly the most distinctive European representative of the highly adaptable lark family, Alaudidae. It is found widely across much of the northern hemisphere, even penetrating into South America, with a relict subspecies in Colombia. Large and variably distinct populations are found across the Central Asian steppes and the Himalayas, and at its southern extent it also reaches into Mexico and Morocco. It is the only lark found in the New World, having spread there at least 600,000 years ago, and the only member of its family to colonise alpine, tundra and grassland habitats, from sea level up to 5,400 m.

This breeding plumaged male Temminck’s Lark, photographed in Syria in April 2004, is the only other species in the genus Eremophila. Very much a desert specialist, it is the most divergent member of the Horned Lark ‘superspecies’. Photo by Aurelien Audevard.

There are currently two accepted species in its genus, Eremophila, forming a superspecies: E alpestris, the Holarctic Shore Lark, and the monotypic E bilopha, Temminck’s Lark. The latter replaces the former in the arid and desert regions of North Africa and the Near East.

The American name for Shore Lark, Horned Lark, is actually more appropriate, as only the northern Eurasian subspecies flava regularly winters in coastal habitats, while the species’ most obvious feature is its ‘horns’, formed by two pointed black feathers jutting out backwards on either side of the crown, most prominently in males. Black feathers also form a combined mask and moustachial stripe and a wide bib.

Depending on population, the cheeks, forehead, supercilium and throat range from white to yellow. The entire underparts are white, while the upperparts are more cryptic, being either streaked grey-brown or plain and sandy-brown, depending on habitat. Shore Lark is a touch smaller than Skylark, with a longer tail and shorter bill.

Hatchlings emerge from the egg in an altricial state, that is naked and defenceless. However, they soon develop the long legs of many ground-feeding birds, and are able to start chasing their own prey shortly after. Photo by Markus Varesvuo (www.birdphoto.fi).

When making its gently undulating flight away from the observer, the tail has the distinctive arrangement of white outer feathers bordering two acute black triangles, surrounding a brownish rump. The long white vent and black centre to the undertail may also be apparent, resembling Short-toed Lark.

Vocally, all Shore Lark forms have an undistinguished squeaky call, but two singing styles are used: a short territorial phrase, given from a bush or rock, and a longer mating song given during a display flight. For this, the male silently and steeply ascends from a rock or fence post, singing in steps and briefly pausing with its wings closed, before giving the main chirruping and jangling notes while hovering. Finally, it closes its wings and plummets towards the ground at great speed. The duration and composition of the song flight has been found to differ between some subspecies in North America.

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The lark defending

Breeding territories are defended by the male, and they can be very aggressive toward rivals. Claws are used as weapons in the air and they beat each other with their wings on the ground; at least one such fight has ended in death. Shore Lark normally pairs up for one breeding season, but a female has been observed showing fidelity to a recently dead mate, so the short-term bond is obviously strong. The breeding display involves the male drooping his wings and spreading his tail, fluttering and spreading out his black chest patch.

Individuals of the Moroccan subspecies atlas, photographed here at Oukaimeden in the High Atlas, show plumage features that are somewhat intermediate between Shore and Temminck’s Larks.  Photo by David Elliott-Binns.
British Shore Larks, like this bird at Southport, Cheshire, are of the subspecies flava, and occur annually in small numbers. This form has reached the United States and Japan, while nominate alpestris from North America has strayed to Bermuda, and is believed to have occurred in Iceland in 1981, Northern Ireland in 1998 and most recently on St Agnes and Tresco, Scilly, in October 2001. Photo by Steve Young (www.birdsonfilm.com).

The nest is a hollow in the ground, placed to maximise shade away from the wind, and generally built of dry grass and plant stems, lined with feathers, hair and thistle or cottongrass down. Small pebbles and pieces of tree bark are accumulated around this structure.

Breeding occurs between mid-May and mid-July in the north, but may begin as early as mid-February in southern arid populations. Close approach to a nest site can elicit injury feigning by the female, but the birds generally flush from a distance and then pretend to feed unconcernedly but conspicuously in a more passive distraction display.

Depending on latitude, Shore Lark can have one to three broods with two to seven eggs, generally increasing from north to south. Chicks hatch after 10 to 14 days of incubation, naked and defenceless, and are fed by both parents before fledging after nine to 12 days; they fly after 16 to 18 days. Like many ground-feeding birds, they learn to run before they can fly. Mortality is largely due to predation, but they are also parasitised by Brown-headed Cowbird in North America.

A little-known behavioural quirk is that the more northerly American forms habitually dig roosting tunnels in snow up to 30 cm in depth, with a ‘bed chamber’ at the end. Similar behaviour is exhibited in some desert forms – the subspecies ammophila from the Mojave Desert has been observed digging roost holes in the sand behind vegetation. Such behaviour decreases energy loss and risk of predation at night by reducing the exposed body surface area.

Shore Lark largely consumes seeds in winter and insects in summer, happily chasing the more mobile items by walking, running or hopping. The 19th century spread of cultivation and grazing in North America resulted in a huge range expansion that has not been matched in the Palearctic. The last confirmed British breeding pair was in 2003, after more regular breeding in the north and west Highlands of Scotland ceased in 1977.

Northern Holarctic birds are migratory, but southern forms are largely sedentary, undertaking altitudinal migration or local dispersal at best. Prolonged northern snowfall appears to be the initiating mechanism for migration, and the species will form small casual flocks, as either a response to the clumped distribution of edible seeds or for protection against predators.

Shore Larks are very distinctive in flight, having brighter and more clearly defined plumage than most other lark species. Photo by Markus Varesvuo (www.birdphoto.fi).

North-south divides

A quick look at illustrations of the species in a field guide immediately gives rise to suspicions that variation within the species is not fully explained by its current classification. Eremophila as a whole certainly needs a taxonomic overhaul.

Many of the named subspecies in the Americas are clinal and intergrade to varying degrees, and indeed some may be invalid taxa. There is, however, a general grouping of more streaked and redder birds on the west coast, plainer and more pink-toned Arctic birds, and greyer unstreaked birds in the grasslands of the interior – overall plumage tones become lighter from north to south.

Colombian birds of the subspecies peregrina are the most threatened of all subspecies, being reduced to 80 individuals at the last census. This most southerly population has been drastically reduced in number due the expansion of the introduced Kenyan Kikuyo Grass. Photo by Barry Wright.
Armenian birds like this spring male are part of the distinctive  penicillata group of subspecies found in most of the arid lands of the Near East. They can be identified by the continuous black of the moustachial band and throat patch. Photo by Steve Young (www.birdsonfilm.com).
In North America, Shore Lark is known more descriptively as Horned Lark. This bird was photographed in Aragonite, Utah, and is probably of the subspecies utahensis. Photo by Nigel Forrow.

A similar pattern occurs in the Palearctic, with light grey-brown streaked birds in the north, paler steppe forms, and plainer, sand-coloured arid forms to the south in the penicillata group found from the Balkans to the Near East.

However, plumage tone appears to change to suit habitat throughout the species, blurring the distinction between genuine subspecies and ecological morphs. Variation in face coloration in each form is of little use in distinguishing between anything other than the main subspecies groups. Tentative results from unpublished genetic analyses hint that Eremophila is composed of three to four clades (groups of organisms derived from a common ancestor). There is a weakly supported divergence in the nominate alpestris group between Nearctic and Palearctic birds, perhaps more so when song and call types are taken into account. However, the paler-plumaged Near Eastern penicillata group and Temminck’s Lark appear to be more strongly divergent. The latter has long been split, but a holistic approach suggests that each group may be a ‘split-in-waiting’.

Some subspecies have certainly been found to be discrete and definable; for instance, arcticola from Alaska appears not to intergrade, and strigata from the Pacific north-west is sufficiently genetically unique to have its own conservation strategy. Needless to say, more work with multiple samples from all subspecies and regions is needed before any robust revisions are made.

Much of the variation is ecological: desert forms have longer legs, migratory forms have longer wings with no overlap in measurements with the sedentary subspecies, and arid forms are slighter in structure, with Temminck’s at one extreme. The cautious might note that too many divisions between the populations might make its taxonomy unmanageable, and also that the extent of intergradation is largely unknown, though some taxa have a very narrow hybrid zone.

Both species are classified as ‘Least Concern’ by BirdLife International, Shore Lark having an estimated total population of at least 140 million. However, some subspecies are under threat. The Colombian peregrina is declining rapidly due to the influence of alien grass species, pesticides and intensive farming; a 2001 census found only 80 individuals. Some of the North American subspecies are of restricted range, and strigata is now being protected at regional level.

Britain’s familiar coastal wintering form, flava, has rapidly declined since the 1950s. Though possibly attributable to overgrazing on its breeding territories, this is not proven.

Mysterious, idiosyncratic and a feast for the eyes, Shore Lark is both attractive to anyone interested in wildlife and subtly variable enough to be a real ‘birder’s bird’. It’s scarce enough in Britain to be worth twitching and to be a good self-found bird. Why not go out and see this birding all-rounder before the winter’s out?

Acknowledgement

Thanks to Laurent Raty for analysing published gene sequences and constructive commentary.

References

For a full list of references, please click here.