Population decline is linked to migration route in the Common Cuckoo

Abstract

Migratory species are in rapid decline globally. Although most mortality in long-distance migrant birds is thought to occur during migration, evidence of conditions on migration affecting breeding population sizes has been completely lacking. We addressed this by tracking 42 male Common Cuckoos from the rapidly declining UK population during 56 autumn migrations in 2011–14. Uniquely, the birds use two distinct routes to reach the same wintering grounds, allowing assessment of survival during migration independently of origin and destination. Mortality up to completion of the Sahara crossing (the major ecological barrier encountered in both routes) is higher for birds using the shorter route. The proportion of birds using this route strongly correlates with population decline across nine local breeding populations. Knowledge of variability in migratory behaviour and performance linked to robust population change data may therefore be necessary to understand population declines of migratory species and efficiently target conservation resources.

Conditions at autumn stopover sites affect survival of a migratory passerine

“…Future studies estimating survival values for Reed Warblers wintering in Africa would enable a more accurate estimation of mortality rates during migration. Intriguingly, our results and conclusions are in agreement with a recent study of satellite-tracked Common Cuckoos Cuculus canorus that showed precisely where bird mortality occurred (Hewson et al 2016). The authors found that most of the mortality of Common Cuckoos on the Western migratory route occurred in Europe, prior to completion of the Sahara crossing, leading them to suggest that deteriorating conditions at stopover sites in Spain and Morocco were responsible for the decreased survival.…”

“…low food availability), it seems likely that a large proportion of the mortality which occurs in avian species is associated with this stage of the annual cycle. Several studies have provided evidence for this hypothesis (Newton 2006;Bayly et al 2011;Klaassen et al 2014, Hewson et al 2016. For example, Sillett and Holmes (2002) estimated that mortality rates of Blackthroated Blue Warblers Dendroica caerulescens were at least 15-fold higher during migration than during stationary periods.…”

“…Baker et al (2004) found that foraging conditions in Delaware Bay, an important stopover site for Red Knots Calidris canutus before their departure to their Arctic breeding grounds, deteriorated considerably due to the overharvesting of crabs whose eggs are the main food of the species there, resulting in a decreased survival of adults and, consequently, a population decline. Hewson et al (2016) noted that the migratory Common Cuckoos Cuculus canorus, which breeds in the UK, experienced its highest mortality at stopover sites in Spain where climatic and environmental conditions have changed considerably in recent years, having become more arid as a result of climate change.…”

“…Any adverse environmental changes occurring at these crucial stopover sites may have severe consequences for the survival of such species. To our knowledge, only a few studies to date have investigated and found some effect of conditions at stopover sites on the survival of migratory birds (Baker et al 2004;Hewson et al 2016). Baker et al (2004) found that foraging conditions in Delaware Bay, an important stopover site for Red Knots Calidris canutus before their departure to their Arctic breeding grounds, deteriorated considerably due to the overharvesting of crabs whose eggs are the main food of the species there, resulting in a decreased survival of adults and, consequently, a population decline.…”

Achteruitgang insectenpopulaties in Nederland: trends, oorzaken en kennislacunes

“…Het aantal locaties met herhaalde waarnemingen in (Halupka et al 2008;Hewson et al 2016;Zwarts et al 2009). Een achteruitgang van insectenpopulaties kan bijdragen aan een neerwaartse populatietrend, maar het is onwaarschijnlijk dat deze zich hierin een-op-een vertaalt.…”