Early Life Events Carry Over to Influence Pre-Migratory Condition in a Free-Living Songbird

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

Hematology and Blood Chemistry of Wintering Common Cranes

5 paginas y 2 tablesWe studied the hematology and blood chemistry of wintering Common Cranes (Grus grus). Red cell numbers (2.460 × 106 mm-3), hemoglobin content (14.8 g/100 ml), and hematocrit (42.9%) were similar in adult and young birds. Young birds have significantly higher leukocyte numbers (28 × 103 mm-3) than adults (22 × 103 mm-3). Heterophils are the most abundant white blood cells in adults (55%) whereas young have the same proportion of heterophils and lymphocytes (47%). Plasma protein levels are similar in young and adult birds (4.9 g/100 ml), as is the plasma cholesterol level (200 mg/100 ml). However, adults have higher plasma urea levels and lower uric acid and plasma triglyceride levels than young birds (7.1 vs. 5.5 mg/100 ml, 2.9 vs. 4.4 mg/100 ml, and 81 vs. 110 mg/100 ml, respectively).Fieldwork was supported by the DGICYT Project No. PB0389Peer reviewe

Coping with the worst of both worlds: Phenotypic adjustments for cold acclimatization benefit northward migration and arrival in the cold in an Arctic-breeding songbird

Cold acclimatization (phenotypic adjustments to cope with cold conditions) is an imperative requirement for birds living at high latitudes during the cold depths of winter. Despite the significant remodelling of key phenotypic traits and energetic costs associated with elevating cold endurance, winter cold acclimatization can also provide further carryover benefits to subsequent stages in species wintering, migrating and breeding in cold environments (e.g. the Arctic). We tested this beneficial carryover hypothesis using outdoor captive Arctic-breeding snow buntings Plectrophenax nivalis, a cold specialist known for its impressive wintering thermogenic capabilities. We compared changes in phenotypic traits supporting cold acclimatization—body composition (body, fat, lean mass, pectoral muscle thickness), oxygen carrying capacity (haematocrit), thermogenic capacity and endurance (Msum, time to Msum), cold tolerance (Ta at Msum) and maintenance energy expenditure (BMR)—between the wintering, migratory and arrival/summer stages. Body mass (+31%), fat mass (+226%) and BMR (+13%) increased relative to the winter phenotype, likely to support the added costs of migration—that is the migratory upregulation hypothesis. In contrast, lean mass, pectoral muscle thickness, haematocrit and thermogenic capacity remained high and stable at winter level across stages in support of the thermal carryover hypothesis. The maintenance of these traits likely offers spare capacity for unpredictable cold environments expected during migration and breeding in the Arctic. Our results thus suggest that birds can extend the long-term advantages of winter phenotypic adjustments through additional benefits to thermogenic capacity during subsequent life-history stages. These benefits likely make it possible for Arctic-breeding birds to maximize success across diverse life-history stages in the face of extreme cold conditions