Abstract
Conditions experienced during development can have long-term consequences for individual success. In migratory songbirds, the proximate mechanisms linking early life events and survival are not well understood because tracking individuals across stages of the annual cycle can be extremely challenging. In this paper, we first use a 13 year dataset to demonstrate a positive relationship between 1st year survival and nestling mass in migratory Savannah sparrows (Passerculus sandwichensis). We also use a brood manipulation experiment to show that nestlings from smaller broods have higher mass in the nest relative to individuals from larger broods. Having established these relationships, we then use three years of field data involving multiple captures of individuals throughout the pre-migratory period and a multi-level path model to examine the hypothesis that conditions during development limit survival during migration by affecting an individual's ability to accumulate sufficient lean tissue and fat mass prior to migration. We found a positive relationship between fat mass during the pre-migratory period (Sept–Oct) and nestling mass and a negative indirect relationship between pre-migratory fat mass and fledging date. Our results provide the first evidence that conditions during development limit survival during migration through their effect on fat stores. These results are particularly important given recent evidence showing that body condition of songbirds at fledging is affected by climate change and anthropogenic changes to landscape structure.
Highlights
Conditions experienced during early development, such as poor nutrition, can have long-term consequences for an individual’s phenotype, subsequent performance, and fitness [1,2,3]
Because juveniles move large distances prior to migration [21,22], are difficult to track during migration, and because natal dispersal can be broad in extent [23,24], documenting the proximate mechanisms linking conditions during development with 1st year survival has been challenging
We lack a validated model for both our measures of total body water and our index of fat mass, we suggest both measures of body condition are robust
Summary
Conditions experienced during early development, such as poor nutrition, can have long-term consequences for an individual’s phenotype, subsequent performance, and fitness [1,2,3]. Many of these long-term effects occur over varying time scales and under specific ecological contexts [3]. Survival until the following breeding season (hereafter 1st year survival) tends to be positively correlated with nestling mass (12 of 14 species reviewed; [8], [18,19], see [20]) Together, these studies suggest that conditions during development can affect 1st year survival in migrants. Because juveniles move large distances prior to migration [21,22], are difficult to track during migration, and because natal dispersal can be broad in extent [23,24], documenting the proximate mechanisms linking conditions during development with 1st year survival has been challenging
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