Breeding biology of Skylarks Alauda arvensis in maize and other crop fields

The Skylark populations are declining in most European agricultural landscapes. Changing crop compositions and seasonal vegetation dynamics have been suggested to influence the breeding success of Skylarks in arable fields. We quantified the breeding performance of Skylarks by means of continuous video surveillance in maize fields (n = 83 nests) and in a pooled sample of other crops, mostly sugar beet, opium poppy and cereals (n = 89 nests), in the Czech Republic, from 2009 to 2011. Skylarks colonized the bare ground of maize fields immediately after sowing and continued to breed there until the end of the breeding season in late July. The vegetation height at the time of laying did not exceed 100 cm, but late broods left nests under maize reaching up to 210 cm. In spite of similar clutch sizes, a lower number of chicks fledged per successful nest in maize fields compared to other crops, as a consequence of the lower hatchability and higher partial nestling mortality. Nest success (based on daily survival rates) was very low ranging from 8% (raw estimate) to 12% (model estimate), while the difference between crops was less than 1%. The nest productivity was less than 0.4 chicks produced per nesting attempt in both crops. At least 84% (maize) and 65% (other crops) of primary nest losses were caused by predation. After controlling for vegetation height, there was little difference in nest survival between crops during the egg stage, but nest survival was marginally lower in maize during the nestling stage. Results of the study suggest that the recent increasing area of energy cropping fields represented mainly by maize provide an attractive, yet risky, nesting habitat for Skylarks, especially late in the season when autumn-sown crops are too dense. The main factor responsible for the low nesting success is the high rate of nest predation, regardless of vegetation height, as a consequence of shift from mainly avian to mammalian predation towards the end of breeding season.