Habitat use and diet of skylarks Alauda arvensis wintering on lowland farmland in southern Britain

Abstract

Summary 1.The habitat use and diet of skylarks wintering on lowland farms were studied to assess whether changes in agricultural practice could have reduced their most favoured wintering habitats or foods. Faecal samples were collected and soil seed densities were estimated. Skylarks in 122 cereal stubble fields in Oxfordshire were counted monthly to examine habitat use. 2. Cereal stubble fields were more likely to be occupied than other crops, and densities of birds in occupied fields were high. Barley stubbles were significantly more likely to be occupied than wheat stubbles. Growing cereals were weakly selected. Sugar beet stubbles held high densities of birds. Rotational set-aside was occupied more frequently and held higher densities than non-rotational set-aside. 3. Field size affected field occupancy independently of crop type, with larger fields more likely to be occupied. Fields enclosed by hedges or trees tended to be avoided. Cereal and set-aside fields that were occupied by skylarks in at least 1 month held significantly higher soil seed densities than fields that were not occupied. 4. Differences in occupancy between crops could be explained by diet. Birds in cereal stubbles fed largely on cereal grain, whereas those in winter cereals fed largely on cereal leaves. Broad-leaved weed leaves were strongly selected as food in cereal crops and farmland grass fields. In grass fields, the proportion of the diet made up by broad-leaved weeds was positively correlated with their availability. Broad-leaved weed seeds did not make up a significant dietary component in any crop. 5. Our results show that the shift from spring to autumn sowing of cereals has led to a loss of the skylark's most strongly selected wintering habitat and best food source. In winter cereals and in grass there was a high selectivity for relatively scarce, and probably declining, food resources. Our results suggest that the retention of weed-rich cereal (particularly barley) and sugar beet stubbles through the winter, particularly in large open blocks, will improve conditions for skylarks in winter. Whole-field rotational setaside, particularly as naturally regenerating cereal stubbles, provides good winter food resources for skylarks.

Habitat selection by SkylarksAlauda arvensiswintering in Britain in 1997/98

“…In this study, cereal crops were used in proportion to availability and previous studies have ranged from reporting limited selection (Donald et al 2001) to avoidance (Wilson et al 1996, Buckingham et al 1999, Robinson & Sutherland 1999. Contrary to Wilson et al (1996), this study found positive selection of oilseed rape crops and stubbles and root crop stubbles.…”

“…Cereal stubble fields, especially those with abundant weeds, were the most positively selected farmland habitat type as found by Wilson et al (1996), Chaney et al (1997), Wakeham-Dawson & Aebischer (1998), Buckingham et al (1999), Robinson & Sutherland (1999), and Donald et al (2001). No difference was found between barley and wheat stubbles despite the fact that barley stubbles support greater cover of crop volunteers and broadleaved weeds (Robinson & Norris 2001).…”

“…In winter, Skylarks have a broad diet consisting of a variety of small seeds, fresh vegetation and germinating seedlings. However, when feeding in cereal crops they consume mostly cereal leaves, whereas on stubble fields they consume mostly seeds, especially grain (Green 1978, Robinson 1997, Donald et al 2001. This difference presumably reflects the fact that spilt cereal grain and weed seeds occur at lower densities in germinated cereal crops compared with stubble fields (Robinson & Sutherland 1999).…”

“…No difference was found between barley and wheat stubbles despite the fact that barley stubbles support greater cover of crop volunteers and broadleaved weeds (Robinson & Norris 2001). Furthermore, two studies found greater selection of barley stubbles than wheat stubbles (Buckingham et al 1999, Donald et al 2001.…”

“…We set out to quantify the availability and use of habitat by Skylarks across lowland Britain and to complement intensive winter studies carried out on individual farms (e.g. Wilson et al 1996, Buckingham et al 1999, Robinson & Sutherland 1999, Donald et al 2001.…”