How to recover after sea crossing: the importance of small islands for passerines during spring migration

Abstract

Every year, billions of migratory birds cover thousands of kilometers between their wintering grounds and their breeding areas. Along their migratory route, birds are often forced to break up their journey into several legs, mainly in correspondence with ecological barriers (e.g. seas and deserts), and stopover in areas where they can sleep and rebuild their energy stores. Stopover is a key migratory stage for many songbirds because strategies adopted at this stage may have direct bearing on the success of migration and, consequently, on the fitness of the individual. Although the restoration of energy reserves is likely the main goal for stopover in many cases, our recent studies suggest that there might be other reasons for stopping over, particularly after long non-stop flights. This seems to be the case of millions of songbirds that land on small coastal islands after crossing large waterbodies, although most of these sites do not provide sufficient refueling opportunities. Here, we aim to provide a new perspective on the role of such small islands by reviewing our recent findings on energy management in migratory songbirds. We are convinced that understanding the role of these islands for migratory birds, as well as how birds manage their energy at these sites, represents an important step toward an optimization of conservation strategies, since setting priorities for protection based on food availability alone may miss critical functions of stopover sites.

Modularity in temporal co-occurrence networks at a stopover site reveals strong co-migration fidelity in African-European migratory landbirds over time

“…Overall, stopover areas are important to replenish energetic reserves, where the availability of suitable habitats can influence the subsequent flight range (Bayly et al, 2013; Gómez et al, 2017). However, stopover sites can have different functions not exclusively related to foraging, as their ecological context (e.g., proximity to ecological barriers, spatial isolation) and intrinsic characteristics (e.g., diversity and abundance of resources) may determine the use made by migrants (Mehlman et al, 2005; Maggini et al, 2020; Ferretti et al, 2021).…”

“…Although co-occurrence patterns cannot be used to infer real interspecific interactions, they can reveal the emergence of potential interferences among species, especially when these are forced to share small areas in limited time frames, such as in migratory bottlenecks. This is the case of stopover areas, where birds stop to rest, refuel and seek shelter during their migration activity, and where the decision on where, when and how long to rest is driven by physiological adaptations associated with migratory behaviour and habitat quality (Fusani et al, 2009; Lafleur et al, 2016; Ferretti et al, 2021). For instance, the amount of forest cover and productivity relates to the two-step mechanism determining the spatiotemporal use of stopover areas, by serving as cues to identify high-quality habitat prior to landing and by sustaining refuelling rates of migrants (Buler & Moore, 2011; Lafleur et al, 2016).…”

“…characteristics (e.g., diversity and abundance of resources) may determine the use made by migrants (Mehlman et al, 2005;Maggini et al, 2020;Ferretti et al, 2021).…”

“…This is the case of stopover areas, where birds stop to rest, refuel and seek shelter during their migration activity, and where the decision on where, when and how long to rest is driven by physiological adaptations associated with migratory behaviour and habitat quality [60][61][62]. For instance, the amount of forest cover and productivity relates to the two-step mechanism determining the spatiotemporal use of stopover areas, via identification of high-quality habitat prior to landing and sustained refuelling rates during stopover [61,63]. Overall, stopover areas are important to replenish energetic reserves and can influence subsequent flight ranges [64,65].…”

Moving towards a far-away goal: a foreword

“…In fact the yearlings of passerine birds on their first migratory journey primarily rely on an inherited spatiotemporal programme to reach their winter quarters by a mechanism of vector navigation. To this inborn directional information, learned components are then added with experience, to form the navigational systems that drive their successive migratory courses (see the contributions of Åkesson et al 2021;and of Ferretti et al 2021).…”