A POPULATION STUDY OF SKYLARKS ALAUDA ARVENSIS

Abstract

SUMMARY A population of colour‐ringed Skylarks Alauda arvensis was studied intensely over two and less thoroughly over another five breeding seasons in Kavenglass, Cumberland. The breeding season extends from mid‐April to early July, but the onset, which is well synchronized, varies from year to year, probably depending on the spring temperature. One‐year‐olds lay the first clutch about a week later than older birds. Within a group of females there is a constancy in the laying order of first clutches from year to year. The rank of any given female seems to depend on an individual temperature threshold, which is reached four to seven days before laying, but other factors must play a role. The interval between the disappearance of a clutch or brood and the laying of the next clutch varies from four to six days depending on the stage at which the previous brood was lost. Beyond the 17th or 18th day of life the chicks of one brood no longer prevent the laying of a new clutch. No factors influencing the end of the season could be found. On average, Skylarks lay 2.7 clutches per year (range 1–5). Three successful broods seems to be the maximum. Average c/size is 3.69 eggs (range 3–5). The c/size varies with successive clutches, from 3.3 for first, to 4.0 for third clutches. Individual females tend to lay clutches of a characteristic size. No difference could be found between the clutches of one‐year and older birds, Females which retain the same territory from year to year show more consistency in clutch size than those which change territories. Data from different geographical locations in Europe suggest a cline from northwest to southeast of increasing clutch size. Clutch size does not seem to be affected by temperature. The variability of egg size and shape is discussed. 68% of the eggs laid hatched (incubation period 11 days) and 67% of the young hatched left the nest on the 8th day. About 90% of the eggs and young lost were taken by predators. No consistent seasonal differences in nest mortality could be found, nor between c/3 and c/4. An incidental experiment suggests that predation of Skylark nests is density dependent. The success of one‐year‐old females in rearing nest‐leaving young is lower than that of older birds (15% compared with 51%). From observations of the feeding behaviour of the parents it is estimated that about 25% of the young survived to flying age (16th day of life), and about 10% reached independence (30th day). Skylarks, males more than females, exhibit a strong site‐tenacity. One‐year‐old birds tend to return to the birthplace area. Associated with site‐tenacity the Skylarks show mate‐faithfulness. Of 36 pairs 17 remained faithful from one year to the next. During a breeding season mate‐faithfulness is practically absolute. There is a correlation between the breeding success of a pair and the likelihood of the pair remaining together the following year. Mean annual adult mortality was 33.5%, with little variation except in 1962/63 (47%‐the result of a hard winter). After reaching independenc...

The use of tongue spots for ageing and wing length for sexing SkylarksAlauda arvensis– a critical evaluation

“…Wing lengths of Skylarks from our breeding population are very similar to those described by Delius (1964Delius ( , 1965) for a population in northwest England. He found female wing length to range from 95-108 mm and male wing length from 105-118 mm.…”

“…Also, for other species, problems and pitfalls of relying on biometric data for sexing have been described, with sexual dimorphism varying in time and space (Van de Pol et al 2009). To the best of our knowledge only Delius (1964Delius ( , 1965 showed the existence of males with short wings on live birds in the field, even though other studies have revealed their existence on skins (Svensson 1992, Dougall 1998. Given the criteria many ringers across Europe use for sex determination (eg Svensson 1992, Speek 1994, Demongin 2006, Winkler & Jenni 2007, small males in particular are likely to be misclassified.…”

How to identify dear enemies: the group signature in the complex song of the skylarkAlauda arvensis

“…Skylarks display strong site fidelity within and between breeding seasons. Thus, both male and female have a strong tendency to return to the same breeding location from year to year (Jenny, 1990), and 1-year-old males show regional philopatry (Delius, 1965). Males display strong territorial behaviour, and intense fights are elicited by newcomers that seem to be harassed, not only by nearby territory owners but also by skylarks from further afield (Delius, 1965).…”

“…Thus, both male and female have a strong tendency to return to the same breeding location from year to year (Jenny, 1990), and 1-year-old males show regional philopatry (Delius, 1965). Males display strong territorial behaviour, and intense fights are elicited by newcomers that seem to be harassed, not only by nearby territory owners but also by skylarks from further afield (Delius, 1965). As part of this territorial behaviour, males produce a flight song to deter intruders (Delius, 1963;Hedenström, 1995), in which species identity is encoded by temporal parameters (Aubin and Brémond, 1983).…”

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

“…Assuming that the same return rates apply to our study population, it would require on average three fledglings per pair per year in order to maintain the population size. With 2.5-3 breeding attempts per year (Delius 1965), the minimum number of fledglings required per breeding attempt is 1.0-1.2. In our study area, the mean number of fledglings produced per breeding attempt-averaged over all study years and all breeding habitats-was only 0.5, and this is probably an underestimate because nests that fail during the early nesting stages are often missed (Jenny 1990).…”