Individual consistency of long‐distance migration in a songbird: significant repeatability of autumn route, stopovers and wintering sites but not in timing of migration

Abstract

Through new tracking techniques, data on timing and routes of migration in long‐distance migrant birds are accumulating. However, studies of the consistency of migration of the same individuals between years are still rare in small‐sized passerine birds. This type of information is important to understand decisions and migration abilities at the individual level, but also for life history theory, for understanding carry over effects between different annual cycle stages and for conservation. We analysed individual repeatability of migration between years in great reed warblers Acrocephalus arundinaceus; a medium‐sized European songbird migrating to sub‐Saharan Africa. In seven males, with geolocator data from 2–4 yr per bird, we found low to moderate (non significant) repeatability in timing of migration parameters (R ≤ 0.41), but high (and significant) repeatability for most spatial parameters, i.e. autumn route (R = 0.64) and stopover sites (R = 0.59–0.87) in Europe, and wintering sites (R = 0.77–0.99) in sub‐Saharan Africa. This pattern of high spatial but low temporal within‐individual repeatability of migration between years contrasts other tracking studies of migrating birds that generally have found consistency in timing but flexibility in routes. High spatial consistency of migration in the great reed warbler may be due to it being a specialist in wetlands, an unevenly distributed habitat, favouring a strategy of recurrence at previously visited sites. Low temporal repeatability may be caused by large between‐year variation in carry‐over effects from the breeding season, high flexibility in decision rules during migration or high sensitivity to environmental factors (weather, wind) during migration.

Barometer logging reveals new dimensions of individual songbird migration

“…The travel segments were three segments in Europe and Africa for the red-backed shrike and two segments for the great reed warbler (Table 1, Fig. 1; the birds' regional locations were broadly estimated from the autumn migratory routes as demonstrated by earlier geolocator studies in Tøttrup et al 2012, Lemke et al 2013, Hasselquist et al 2017. Both birds completed all travel segments in high pressure conditions and the comparison showed that the SA heights were underestimated for the times and regions of the two individuals in this study.…”

“…In this study we did not use these data since some light level recordings either had failed or were of poor quality. When approximating regions for comparison of standard atmosphere estimates and geopotential heights of altitudes, and when describing the flight segments of the birds, we used earlier published spatiotemporal patterns from individuals of the same populations of red-backed shrikes (Tøttrup et al 2012) and great reed warblers (Lemke et al 2013, Hasselquist et al 2017.…”

“…In this study we use data loggers to monitor pressure, movement and temperature along the whole autumn migratory journey of two individual songbirds, one redbacked shrike Lanius collurio and one great reed warbler Acrocephalus arundinaceus. Both these species breed in Europe and winter in sub-Saharan Africa (Tøttrup et al 2012, Lemke et al 2013, Hasselquist et al 2017. We illustrate four aspects of songbird migration that become available for analysis based on the new combined barometer/accelerometer/temperature information -1) flight altitudes, 2) ground elevations where the birds stay and forage before and after migration as well as during stopover and resting in between the migratory flights, 3) relationships between barometric pressure changes and the birds' probability of departure on migratory flights and 4) relationships between flight altitude or ground elevation (when the bird is on the ground and not in migratory flight) and data logger temperature.…”

“…Flight altitudes, and altitudes of stationary periods, in a great reed warbler (a-b) and a red-backed shrike (c-d). Migratory routes, and breeding, stopover and wintering areas, of the great reed warbler and the red-backed shrike are indicated on the topographic map (e; modified fromTøttrup et al 2012, Lemke et al 2013, Hasselquist et al 2017. Colours indicate the different travel segments: the first segment within Europe for both individuals (yellow), the second segment to western Africa (red) for the great reed warbler, and the second segment (blue) and the last segment from Sahel to southern Africa (dark blue) for the red-backed shrike.…”

Non-random association of MHC-I alleles in favor of high diversity haplotypes in wild songbirds revealed by computer-assisted MHC haplotype inference using the R package MHCtools

“…We used empirical data on 141 adult males, 131 adult females, and 287 chicks from our long term study population of great reed warblers breeding at lake Kvismaren (59°10'N, 15°25'E) in southern Central Sweden Hasselquist, Montras-Janer, Tarka, & Hansson, 2017;Roved et al, 2018). The adult individuals in our data set have been observed, examined, and ringed in the period 1984-2004, and the chicks constitute the 1998 and 1999 cohorts from the same population, with addition of one nest from each of the years 1992 and 1996 (cf.…”