Migratory routes, breeding locations and multiple non-breeding sites of Common Whitethroats Curruca communis revealed by geolocators

Abstract

Understanding general migration characteristics and how breeding and non-breeding sites are connected is crucial for predicting the response of long-distance migratory bird populations to environmental changes. We use data collected from six geolocators to describe migratory routes and identify breeding and non-breeding locations, migratory behaviour and differences between spring and autumn migration of Common Whitethroats Curruca communis, an Afro-Palearctic migrant, wintering in Nigeria. Most individuals departed on spring migration in April, following a north-easterly direction, arriving at their breeding grounds across central-eastern Europe (~425,000 km2) in May. Departures from breeding grounds took place between July and August in a south-westerly direction. During spring migration individuals travelled longer distances at faster rates making its overall duration shorter than autumn migration. We suggest that, while Whitethroats can cross the Sahara Desert and Mediterranean Sea in a single flight, they are likely to refuel before and after crossing. Results indicate that Whitethroats undertook loop migration and visited two wintering sites: first in the Sahel, then in Nigeria, where they remained until spring migration. Geolocator results and data from the European Union for Bird Migration’s (EURING) ringing database suggest that Whitethroats have a relatively high migratory spread—individuals from a single non-breeding site breed across a wide area of Europe. Our research is the first to track and describe the complete annual cycle of Whitethroats and one of the few studies to do so for any Afro-Palearctic migrant from non-breeding grounds. We identified the Sahel as an important refuelling and first wintering site indicating its conservation, alongside other stopover sites, is crucial for the species. We believe that changes in this region will have severe effects on a subset of individuals of specific European breeding populations, but these effects will greatly depend on the severity of the changes and at what spatial scale they occur.

Seasonal Shifts in Habitat Choice of Birds in the Sahel and the Importance of ‘Refuge Trees’ for Surviving the Dry Season

“…Birds in eastern and southern Africa have been shown to use consecutive sites that sometimes are thousands of km apart (Lack 1986b, Pearson & Lack 1992, Herremans 1998, Jones 1999). However, in the western Sahel birds may remain in the transition zone between desert and the forest, moving a few hundred km southwards in the course of their wintering period, as shown by GPS-equipped European Turtle Doves (Lormée et al 2016, Schumm et al 2021), Montagu's Harriers (Schlaich et al 2016, Schlaich 2019; see also Buij & Croes 2014, for supportive evidence from field observations on a raptor guild in Cameroon) and also by geolocator-equipped birds, such as Common Whitethroat (Tapia-Harris et al 2022), Northern Wheatears (Arlt et al 2015), Tawny Pipits (Briedis et al 2016) and European Turtle Doves (Eraud et al 2013). Bird counts in Nigeria in November, repeated in February, revealed that out of nine migratory species, three had moved southwards and two had moved northwards (Cresswell et al 2009).…”

Common Whitethroats Curruca communis show a continuum of residency duration but a high degree of between‐years site fidelity at nonbreeding grounds in Nigeria

“…We cannot, however, provide evidence for this, as we do not know whether individuals categorized as “passage” or “unknown” at our study site remained itinerant throughout the season, if they were in fact en route to a stationary nonbreeding site elsewhere, or if they died during the period. These genetic differences could also reflect individuals from different breeding populations, but this seems highly unlikely because individuals switched strategies across years, and Whitethroats seem to have a somewhat low migratory connectivity (Tapia‐Harris et al, 2022 ).…”

“…Short‐term residencies, during both autumn and spring, may indicate the use of multiple important nonbreeding sites. Nigerian Whitethroats deployed with geolocators remained at the first stationary nonbreeding site in the Sahel before arriving at our study site in November (Tapia‐Harris et al, 2022 ). If some of these birds were then to be short‐term residents, individuals could have more than two important stationary nonbreeding sites.…”

“…Departure from the nonbreeding grounds has been seen to correlate with arrival at breeding sites (Kristensen et al, 2013 ; Ouwehand & Both, 2017 ), though later departing individuals can migrate faster to compensate for lost time (Yohannes et al, 2009 ). As our study site is located in the southern part of the distribution and individuals have different breeding sites, the first individuals to depart are not necessarily the first to arrive at their respective breeding grounds (Tapia‐Harris et al, 2022 ).…”

The Gap of Chad, a Dearth of Migratory Birds in the Central Sahel

“…There are six predictions. (1) The Gap of Chad really exists, with lower densities of Eurasian migrants compared to West and East Africa, especially in species which make a detour (Western Bonelli's Warbler; Cramp 1992, Cramp & Perrins 1993, Pilastro et al 1998, Gargallo et al 2011), but (2) the Gap of Chad will be less striking for species which cross the Mediterranean in broad front, such as Common Whitethroat (Tapia-Harris et al 2022), Common Redstart and Woodchat Shrike, if existing at all.…”