More than just refuelling: lengthy stopover and selection of departure weather by sandpipers prior to transoceanic and transcontinental flights

On their journey to wintering or breeding sites, migratory birds usually alternate between migratory flights and stopovers where they rest and refuel. Actually, migrating birds spend most of the time at stopovers. Consequently, selection to minimize total time spent on migration likely operates mainly on the effectiveness of stopover rest and refueling. Departure probability from stopover sites depends both on weather conditions and fuel stores, but their respective role has not been quantified. In the present study, we assess the relative contribution of factors driving the departure decision from a stopover site. As we cannot reliably characterize body condition and restness when capture probability is low, we propose to use the Time Since Arrival (TSA) as a proxy of the changes through days of the internal state of stopovering birds. We developed a specific capture-recapture model to quantify the relative contribution of TSA and climatic conditions on a 20-year capture-recapture dataset of a long-distance migratory songbird (Sedge warbler). The effect of TSA has yet the major contribution to departure probability compared to weather conditions. Here, low humidity and an increase of atmospheric pressure in the days preceding departure are the weather conditions associated with a higher departure probability but remain secondary compared to the time the individual has already spent at the site. The probability to depart from a stopover site is therefore largely determined by the time that a bird has already spent at the site. Whether this Time Since Arrival is rather a proxy of resting, feeding or fattening efficiency remains to be explored.

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Section: Methodsmentioning

confidence: 99%

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

Roques

Henry

Guyot³

et al. 2020

Preprint

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“…We used a formulation of the Jolly-Seber (JS) model (Jolly 1965, Seber 1965) parameterized with entry probability in the sampling area (Crosbie andManly 1985, Schwarz andArnason 1996). This allows modeling the arrival of birds at the stopover site and estimating SOD (Lyons et al 2016, Lok et al 2019, Roques et al 2021. The parameters of the model are as follows: ϕ t is the probability of staying in the sampling area from day t to t + 1; η t is the probability of arriving at the stopover area on day t given that the individual was not present in the site before; and pt is the probability of capturing the individual on day t given that the individual has arrived and has not yet left the site.…”

Section: Modeling and Statistical Analysesmentioning

confidence: 99%

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

Roques

Henry

Guyot³

et al. 2021

Ornithology

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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.

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“…Semipalmated sandpipers launch their long over‐Atlantic flight to South America from these regions, for which a staging period of several weeks is required (Pfister et al 1998). In complete contrast to the historical situation (Roques et al 2021), this now involves prolonged exposure to peregrines.…”

Section: Inherent Risk and Migratory Cautionmentioning

confidence: 89%

“…Southbound semipalmated sandpipers face a very different predator regime. Their southward passage along the Atlantic flyway is virtually complete before the arrival in mid‐ or late September of migrant peregrines from northern breeding areas (Lank et al 2003, Roques et al 2021), so there is little temporal overlap. But, as part of conservation efforts that began in the mid‐1970s, captive‐raised peregrines were released and induced to breed on the major Atlantic coast staging regions, including the Bay of Fundy (Hope et al 2020), Delaware Bay and Chesapeake Bay (Watts et al 2015), where peregrines have historically bred little or not at all.…”

Section: Inherent Risk and Migratory Cautionmentioning

confidence: 99%

Danger, risk and anti‐predator behavior in the life history of long‐distance migratory sandpipers

Ydenberg

Tavera

Lank

2022

Journal of Avian Biology

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Two recent and independent studies both estimate substantially lower survival rates of semipalmated Calidris pusilla than of western C. mauri sandpipers, consistent with the pronounced multi-decade population decline of the former. Migratory danger has climbed steadily for both these long-distance migrants since the mid-1970s as the number of peregrine falcons Falco peregrinus increased. These predators are present on the Pacific flyway as co-migrants and are a natural (though now more abundant) feature of western sandpiper southbound migrations. Adjustments to migratory speed, timing and routing enable them to mitigate the danger. On the Atlantic flyway peregrines were introduced and breeding populations established in the 1980s at key staging areas, creating a novel hazard for southbound semipalmated sandpipers. Adjustments to migratory timing and speed do not aid in eluding such resident predators, and alternative routes are not available. Semipalmated sandpipers as a consequence have few effective defenses to counter this heightened danger, and we hypothesize that migratory mortality has increased, making over-summering (i.e. skipping a breeding season) more advantageous. The risk effects (i.e. the consequent reduction in population growth rate) so generated are substantial, and may be able to account for a large portion of the population decline.

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More than just refuelling: lengthy stopover and selection of departure weather by sandpipers prior to transoceanic and transcontinental flights

Cited by 12 publications

References 54 publications

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

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

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

Danger, risk and anti‐predator behavior in the life history of long‐distance migratory sandpipers

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