Acta Univ Latv (2004) 676: 119–126

Use of biometrical data to study Corncrake Crex crex population in Latvia

Abstract

The Corncrake Crex crex population in Latvia was monitored by capturing 509 individuals in the time period between 1995 and 2003. During the breeding season Corncrakes attracted by playback of the territorial call of the male were captured at night, and during the migration birds were captured by cage traps. Only birds, which were identified as males (n = 498) and captured during the breeding season (May - July) were analyzed, except for variation in size by age, when all birds (including those captured on migration) with known age were used. Wing length of Corncrake males in Latvia varied between 130 mm and 152 mm (mean = 142.1; SD = 4.22; n = 455), tarsometatarsus length between 35.6 mm and 50.0 mm (mean = 40.5; SD = 2.94; n = 181), and weight between 134 g and 182 g (mean = 162.8; SD = 11.1; n = 120). Significant differences (p < 0.01) in wing length were observed in males from Latvia and other European countries, and comparing other countries with each other, but the expected tendency for northern animals of the species being larger than their con-specifics in the south was not clearly observed. The mean value of the wing maximum length in Corncrakes captured in different habitats, increased as follows: crops < pastures < cultivated meadows < uncultivated meadows < abandoned arable land < abandoned grasslands. The differences were statistically significant (p < 0.05), and might reflect the hierarchy of Corncrake males in habitat selection: larger males living in optimal habitats (e.g. abandoned grasslands), smaller – in suboptimal habitats (e.g. crops). Corncrake males captured in different months (May, June, July) had significantly different wing lengths (p < 0.05). This might be explained by immigration of birds from other populations later in season (June and July), when massive hay harvest begins to the south from Latvia (e.g. Poland), causing destruction of Corncrake nests and prohibiting successful re-nesting in the affected territories there.