Survival rates, causes of failure and productivity of Skylark Alauda arvensis nests on lowland farmland

Abstract

This paper analyses data from 995 Skylark Alauda arvensis nests found on lowland farms in southern England from 1996 to 1998. The majority of recorded nest failures were caused by predation except in agricultural grass, where trampling and agricultural operations were equally important. Nest survival rates varied between crop types, nests in cereals being around twice as likely to succeed as nests in grass or set‐aside. In cereals, nest survival rates increased with increasing distance from the nearest tramline and declined over the course of the breeding season. Predator control also had a significant independent effect on nest survival rates. On one farm where many other factors were held constant, a highly significant increase in nest survival rates from 12.3% to 40.7% coincided with the introduction of intensive predator control, which also appeared to bring forward mean laying dates. Most environmental factors explaining significant variation in nest survival rates did so only at the chick stage. The mean number of chicks produced per nesting attempt was 1.26 in cereals, 0.78 in set‐aside and 0.63 in grass, the differences being due primarily to variation in nest survival rates. Low densities of Skylark territories in cereal crops are not therefore the consequence of low breeding success at the scale of the individual nest and probably reflect limitations on the number of attempts made in a season. Measures taken to improve the attractiveness of cereal crops as a nesting habitat for Skylarks, and beneficial changes in grassland management, are likely to increase overall productivity.

Summer utilization of Oilseed Rape by Reed BuntingsEmberiza schoeniclusand other farmland birds

“…After April, most autumn-sown rape becomes tall and dense and most tramlines are obscured. Skylark nests close to tramlines in cereal crops have higher predation rates, presumably due to increased accessibility to predators (Donald et al 2002). Survival rates of Reed Bunting nests in the Trent Valley were positively related to the amount of cover over and around nests, which tended to be greatest in rank or emergent vegetation, intermediate in rape and lowest in cereals and set-aside (Brickle & Peach 2004).…”

Effects of breeding habitat and field margins on the reproductive performance of Skylarks (Alauda arvensis) on intensive farmland

“…Grassland was one of the most commonly used breeding habitats, but, in line with earlier work, nest survival rates in grassland were very low (Jenny 1990;Wilson et al 1997;Donald et al 2002). The studied fields were cut in their entirety to collect silage every 33 days on average, a time interval that is generally too short for Skylarks to complete their nesting cycle.…”

“…Based on our findings, we see two main possibilities for increasing the availability of safe nesting habitat for Skylarks in the study area and in similar agricultural landscapes. First, the safety of grassland as a breeding habitat could be improved by reducing the number of silage cuts, preferentially in combination with lowered inputs of fertilizer to reduce grass growth, thereby lengthening the cutting interval and allowing the birds more time to raise their brood (Wilson et al 1997;Vickery et al 2001;Donald et al 2002;Stein-Bachinger and Fuchs 2012). This is particularly important because Skylarks greatly prefer grassland as a breeding habitat, especially in June and July when winter wheat becomes too tall and other suitable crops are only scarcely available.…”

“…The overall survival S (the chance that an egg survived through fledging) was estimated as S = H(L 8 ) (F 22 ), where H is the proportion of the eggs that hatch, L is the daily nestling survival rate, F is the daily nest survival rate, 8 is the duration of the nestling phase in days, and 22 is the duration of the nesting period in days (Mayfield 1975). The productivity P (the mean number of fledglings per nesting attempt) was estimated as P = CH(L 8 ) (F 22 ), where C is the mean clutch size and the other variables are as described above (adapted from Donald et al 2002). Standard errors for survival and productivity were obtained by bootstrapping, resampling 10,000 times from the probability distributions for hatching success (beta distribution), nest survival (beta distribution), nestling survival (beta distribution) and clutch size (normal distribution).…”

“…It is known that the breeding performance of Skylarks differs between crops due to differences in food availability and agricultural management (Jenny 1990;Poulsen et al 1998;Donald et al 2002). To increase the effectiveness of field margins, it is therefore important that they are placed alongside crops in which Skylarks have good breeding prospects.…”