Wetenschap - 1 mei 2013

Efforts to save skylark miss the mark

Field margins not always in right places.
Larks prefer to forage less than 100 metres from nest.

8-veldleeuwerik.jpg
8-veldleeuwerik.jpg

Foto: .

Skylarks love field margins. But many of them are in the wrong place for the birds. The skylark is not thriving in the Netherlands. There are estimated to be only 50,000 breeding pairs left: just four percent of the population 50 years ago. The reason is intensive agriculture. Nests are mown into the ground and the food supply is scarce in monoculture fields. For years now, nature managers and farmers have been trying to address this by creating diverse field margins.
But does it help? In other words, what do the larks think of these strips of undisturbed foraging ground? Marije Kuiper investigated this question in the Oldambt area of Groningen province, which full of large-scale arable farms. The lark is one of the few field birds still to be found here. Working with the local working group Grauwe Kiekendief (named after a harrier) Kuiper observed breeding pairs in 73 nests over a period of three years. She carefully documented what they ate, where they got their food from and how far they flew for it.
Wrong crops
 The larks of the Oldambt area have a pronounced preference for field margins. As long as they are not too far from home, that is. If they have to fly more than 100 metres, they make much less use of the field margin. 'But that is not consistent; it depends on the landscape,' explains Kuiper. 'In nature areas, the foraging distance is much smaller.' But on the basis of those 100 metres, Kuiper draws the conclusion that many field margins are not at optimal locations.
Kuiper sees three reasons for this. Some of the field margins are too close together, with the result that possible breeding areas overlap. The fields they run alongside are sometimes full of the wrong crops for skylarks, such as maize or oilseed rape. A further reason is that many of the field margins are too close to roads, forest and water - not territory that is suitable for breeding grounds. Kuiper estimates that the same amount of field margin could potentially serve birds in breeding grounds at least twice as large.

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