What makes the skylark such a special bird?
The fine song is the obvious place to start, delivered with such huge expenditure of energy as the bird soars up to 200 metres into the sky. Each song flight lasts an average of 4 minutes and is subtly different in the ascent, hover and descent so that an experienced listener can tell which phase the bird is in. Longer song flights are more attractive to potential mates in a form of sexual selection that is a plain little brown bird’s equivalent to a peacock’s extravagant plumes.
The nesting season is long and between April and late July, sometimes into early August, pairs will build three or even four different nests in attempts to raise as many broods. Skylarks are unable to sustain populations without three or so breeding attempts. Two to six eggs are laid, usually 4. Adults return to the same territory and their young return to within 20 km of where they were fledged. Territories are about 2-4 hectares depending on habitat and are defended against rival males with a no-man’s land between territories that is not defended.
Vegetation height is important – about 20-40 cms (8” 16”) is optimal but it needs not to be too dense so that the birds can move among it in search of invertebrate prey. Rough grassland 40cms tall is ideal holding 30-40 pairs per square kilometre. Grazed pasture holds only about a fifth of the number. Skylarks will nest in arable crops too and in the UK about 40% of skylarks nest in wheat and barley. However winter-sown cereals are not ideal for skylarks is because after May they become too dense (as well as tall) for skylarks to find their insect food readily. More time finding insects means lower nesting success. This is why skylark plots within winter cereals work so well – they’re foraging areas that help skylarks find chick food easily over the latter part of the summer. Traditional spring sown crops have much greater breeding success. Skylarks do not like trees and avoid nesting within 200 metres of them – it is believed that they offer unwelcome lookout perches for predators.
So why are our skylarks declining? Firstly skylarks are declining nationally and more widely in most parts of Europe and elsewhere across their Eurasian range which extends all the way from Ireland across Europe and Asia to the pacific coast. We know that a big factor is the switch from spring to winter cereals – with the loss of breeding food described above, and the loss of overwintered stubbles that precede spring sowing. Skylarks in grassland systems are struggling too – you only have to look at their UK distribution to see how sparse they are in pastoral areas such as the south-west. Here it’s likely that the cause is mostly the more efficient use of grass forage – either through grazing regimes or silaging. In both cases there is often insufficient vegetation cover for nesting, as well as too little vegetation to support the foliar insects that skylarks depend on during the breeding season.
This impact of more efficient farming is illustrated by the fact that in 2009 populations were reported as stable in Eastern Europe but declining in western and northern Europe. A population map drawn at the time of the fall of the Berlin Wall shows much denser populations in the old East Germany than in the much more intensively farmed West Germany – the contrast follows precisely the line of the former east/west border.
In the UK the decline was 24% in the ten years to 2013. In the Malverns we are faced with a much steeper decline than that, especially on the high hills: the decline in the Northern Hills, historically the skylark’s stronghold was three times higher at 75% over the same period – and now there are none.