Year-Round Tracking of Small Trans-Saharan Migrants Using Light-Level Geolocators

Abstract

Since 1899 ringing (or banding) remained the most important source of information about migration routes, stopover sites and wintering grounds for birds that are too small to carry satellite-based tracking systems. Despite the large quantity of migrating birds ringed in their breeding areas in Europe, the number of ring recoveries from sub-Saharan Africa is very low and therefore the whereabouts of most small bird species outside the breeding season remain a mystery. With new miniaturized light-level geolocators it is now possible to look beyond the limits of ring recovery data. Here we show for the first time year round tracks of a near passerine trans-Saharan migrant, the European Hoopoe (Upupa epops epops). Three birds wintered in the Sahel zone of Western Africa where they remained stationary for most of the time. One bird chose a south-easterly route following the Italian peninsula. Birds from the same breeding population used different migration routes and wintering sites, suggesting a low level of migratory connectivity between breeding and wintering areas. Our tracking of a near passerine bird, the European Hoopoe, with light-level geolocators opens a new chapter in the research of Palaearctic-African bird migration as this new tool revolutionizes our ability to discover migration routes, stopover sites and wintering grounds of small birds.

Estimating Migratory Connectivity of Gray Catbirds (Dumetella carolinensis) using Geolocator and Mark–recapture Data

“…15,16,17 Specifically, geolocators use light sensors, data loggers, and time stamping to quantify light-transition events (sunrise and sunset) and to calculate daily latitude and longitude. 18 Although ).…”

“…For example, recent applications of geolocators to small land birds that utilize dense vegetation suggest that increased error in latitudinal estimates was likely associated with greater shading in understory environments. 16,17 Despite their deficiencies, 19 geolocators represent a significant advance toward understanding the large-scale movement dynamics of birds.…”

“…Following Bächler et al, 17 we set the search radius at 200 km and the grid size at 2 km. We selected the 200-km search radius to encompass point estimates at the upper bound of our observed error (see Table 1).…”

Long-distance bird migration within South America revealed by light-level geolocators

“…We set the search radius at 200 km and grid cell size at 2 km (Bächler et al 2010, Ryder et al 2011) and required ≥24 coordinates to estimate the winter distribution of each bird. For each individual, we present kernel densities encompassing >50%, 50-70%, and 70-95% of the maximum density.…”

Is it possible to acoustically identify individuals within a population?

“…To acquire this knowledge, the locations and movements of animals should be tracked across reproductive seasons or even across many years (Doucette 2010;Lopes et al 2013;Hays et al 2014). In biological studies, individuals are usually physically marked and tracked using radio transmitters (Doucette 2010), satellite loggers (Kennedy et al 2014), geolocators (Bächler et al 2010), colored and numbered bands (Lopes et al 2013;Neubauer et al 2012), tags (Ale et al 2011), medical cautery units (Ekner et al 2011), tattoos or dyes (Nietfeld et al 1994). Physically marking animals requires time, effort, and resources, and researchers have to catch an individual at least once.…”