When to depart from a stopover site? Time since arrival matters more than current weather conditions

Abstract

On the journey to wintering sites, most migratory birds alternate between flights and stopovers, where they rest and refuel. In contrast to the time-minimization strategy commonly assumed to drive the pre-breeding migration, birds are rather expected to follow an energy minimization during post-breeding migration. It is the cumulative duration of flights and stopovers that determines the total energy requirements and duration of the journey. Since migrating birds actually spend most of the time at stopovers sites, selection to minimize the amount of energy or time spent on migration is likely to operate on the effectiveness of stopover rest and refueling. Here, we address the relative contribution of factors acting on departure decisions from a stopover site during the post-breeding migration in a long-distance migratory songbird. When capture probability is low, it is impossible to measure fattening over the entire duration of the stopover. To get around this limitation, we use time since arrival (TSA) as a proxy for the progressive temporal change occurring in the internal state of an individual (i.e. rest, physiological recovery, and fuel loading) during the stopover. We develop a capture–recapture model to address the respective effects of estimated TSA and of weather conditions on departure probability. Using a 20-year dataset for Sedge Warblers (Acrocephalus schoenobaenus), we show that TSA served as a surrogate of the most important information that birds use when deciding to depart from a stopover site, while low humidity and rising atmospheric pressure only slightly increase daily departure probability. Hence, a bird would resume migration mainly according to the time it had to rest and refuel, and then fine-tuning departure decision according to weather conditions. The generality of these results needs to be assessed by applying this modeling framework to other migratory species and at sites or times with greater weather variability.

Elevational differences in migration phenology of Lazuli Buntings do not support selection-based hypotheses for protandry

“…The modeling approach we describe here is well-suited for the high-resolution encounter data provided by our feeders and the observed first/last feeder visits closely corresponded with the estimated arrival/departure dates, suggesting that attracting birds to food resources reduced uncertainty in individual arrivals and departures. We note, however, that the modeling framework we present here can be applied to many other types of encounter data and may be particularly useful in instances where detection probability is lower than in our system, including automated telemetry systems (Taylor et al 2017, Paxton et al 2022) and even traditional band-resighting and recaptures (Roques et al 2022).…”

“…With additional years of data, the modeling framework presented here could be expanded to differentiate between migration departure and permanent loss due to emigration or death and simultaneously model arrivals and departures. If data are available, the model could also be extended to include site-level covariates, such as daily weather conditions, and individual-level covariates including reproductive status or body condition (Roques et al 2022).…”

Carry-Over Effects of Climate Variability at Breeding and Non-Breeding Grounds on Spring Migration in the European Wren Troglodytes troglodytes at the Baltic Coast

“…Conditions at autumn stopover sites are crucial for the rate of migration, as birds spend up to seven times as much time on foraging and resting as they do on flying [ 110 ]. The efficiency of energy accumulation depends indirectly on conditions at stopover sites [ 87 , 111 ]. Warm autumn weather promotes robust vegetation and the availability of insects for migrating birds [ 20 , 82 ].…”

Time trees and clock genes: a systematic review and comparative analysis of contemporary avian migration genetics

“…This event occurs like clockwork, carefully timed to ensure an optimal flight to reach their destination. These annual flight plans are orchestrated to balance day length (Sockman & Hurlbert, 2020), night‐time visibility (Brown & Mewaldt, 1968; Pyle et al ., 1993; Norevik et al ., 2019), and time spent at staging sites (Roques et al ., 2022). The repeated occurrence of this characteristic behaviour on an annual basis with seemingly little deviation has sparked interest in the field of chronobiology, with emphasis on both intrinsic as well as environmental cues contributing to timekeeping in birds (Åkesson et al ., 2017).…”