Are Dutch Skylarks Partial Migrants? Ring Recovery Data and Radio-Telemetry Suggest Local Coexistence of Contrasting Migration Strategies

Abstract

In western Europe, farmland birds have declined in recent decades by almost 50% (BirdLife International 2004, EBCC 2009, PECBMS 2009. While declines are frequently associated with changed or changing conditions during the breeding season and deterioration of the breeding habitat (Newton 2004, Donald et al. 2006, the importance of factors operating outside the breeding season is less clear. However, the general change in agricultural practise from summer to winter cereal and the subsequent loss of overwintering stubble fields is thought to reduce food supply in winter and could reduce survival rates (Donald et al. 2001, Newton 2004, Siriwardena et al. 2007, 2008.In The Netherlands, the Skylark Alauda arvensis is one of the farmland species with the steepest decline: numbers dropped by almost 95% from around 700,000Are Dutch Skylarks partial migrants? Ring recovery data and radio-telemetry suggest local coexistence of contrasting migration strategies In recent years, Skylarks Alauda arvensis have undergone dramatic population declines in many European countries. Evidence exists for deteriorating conditions during the breeding season, but little is known about the situation during the rest of the annual cycle. Here we use two approaches to test if the Dutch breeding population of Skylarks consists of resident and/or migratory individuals. First, we present an analysis of ring recoveries from the Dutch Ringing Centre "Vogeltrekstation". Out of 25 recoveries, 12 Skylarks were resident in winter, 10 migrated and three were classified as probable migrants. Resident birds were accompanied during winter by birds from northern and eastern Europe. Very limited natal and breeding dispersal recorded in the same dataset suggests that our results were not influenced by long dispersal distances. Next, we compared these results to a local radio-telemetry study in the northern Netherlands. During two different years we equipped a total of 27 Skylarks from a breeding population with radio-transmitters and followed them during the subsequent winter. Four birds were found to winter locally. Out of 23 individuals that we did not find in winter, 14 returned in the following breeding season to the study area, all with a working transmitter, suggesting that they wintered outside our study area. Two ring recoveries of birds from the same study population indeed showed migration to south-west Europe. Based on these two lines of evidence, we conclude local coexistence of a resident and a migrant strategy in Dutch Skylarks. The findings of our study are important for the planning of conservation efforts, as we can only protect this rapidly declining species when we know their behaviour and whereabouts throughout the entire annual cycle. (Teixeira 1979, SOVON 2002, van Dijk et al. 2008. In The Netherlands, Skylarks are also common during migration (LWVT/SOVON 2002), and in winter (e.g. Vergeer & van Zuylen 1994, Poelmans & van Diemen 1997, Venema 2001, Bijlsma et al. 2001, Hustings et al. 2006. From the patterns of passage and from ringing...

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“…First, skylarks in our study population are partial migrants: some birds migrate; others winter locally and are accompanied by birds from more northern and eastern breeding populations (Hegemann et al, 2010). With our year-round study focused on the breeding location, we potentially caught a mixture of birds from different populations during wintering and migration.…”

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

“…Outside the breeding season, birds with wing lengths 106-109 mm would have been impossible to sex without molecular methods, while birds from our breeding population with a wing length of 106 mm were certainly females and birds with wings of 108 mm or longer certainly males. This indicates that, during migration and winter periods, we caught populations with at least partly different origin (see also Hegemann et al 2010). It further highlights the difficulties in reliably sexing Skylarks caught during migration or winter.…”

“…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. For example, Dutch Skylarks are partial migrants, with the non-sedentary individuals migrating to or through France (Hegemann et al 2010). Given that French ringers classify birds with a wing shorter than 110 mm as females (Demongin 2006), about 14% of Skylark males originating from the Netherlands are likely to be misclassified as females.…”

Partial migration and decreasing migration distance in the Hungarian population of the Common Blackbird (Turdus merula Linnaeus, 1758): Analysis of 85 years of ring recovery data

“…A remarkably high percentage of these (84%) are reported from Italy. Similarly, hunting in Mediterranean countries contributes a significant number of ring recoveries for migratory bird species breeding in Germany (Fiedler et al 2004) and in the Netherlands (Visser et al 2009, Hegemann et al 2010. It is well known that hunting and illegal trapping of migratory birds can drastically reduce population size (Kamp et al 2015), and alter migratory behavior and routes (Béchet et al 2003).…”

“…However, to objectively decide what could be considered a breeding ground is difficult. One solution to this problem is to plot the distances between the locations of ringing and recovery sites and visually determine the largest gap, a divide between birds recovered relatively close to the ringing site and further away (see Helm et al 2006, Hegemann et al 2010. I considered Blackbirds that fall below this divide as residents and the ones with longer recovery distances as migrants for the purpose of this study (Figure 1).…”