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Data from: Winter food limits timing of pre-alternate molt in a short-distance migratory bird

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Danner, Raymond M.; Greenberg, Russell S.; Danner, Julie E.; Walters, Jeffrey R. (2015). Data from: Winter food limits timing of pre-alternate molt in a short-distance migratory bird [Dataset]. Dryad.


1. Molt is critical for fitness for many organisms for several reasons: it allows growth and maintains the function of the integument for protection, thermoregulation and communication. 2. Feather molt in birds is costly and therefore typically does not overlap with migration or reproduction. In spring, the rapid succession of pre-alternate molt, migration (if a migrant), and breeding suggests that timing of molt could constrain the initiation of breeding. A tradeoff between time spent molting and breeding might also limit molt quality. 3. The proximate basis for the timing of pre-alternate molt initiation is not well known, though it typically occurs during a resource poor time of year. Food limitation combined with fitness consequences of molting earlier suggests that plasticity in timing of pre-alternate molt in response to food abundance should be advantageous. 4. We experimentally tested, for the first time, if food abundance influences the timing of molt in the wild. We conducted a controlled food supplementation experiment on free-living swamp sparrows (Melospiza georgiana) preceding and during the time of natural pre-alternate molt (January–March 2009, 2010). 5. Supplemented birds began molting the body, face, and crown earlier than control birds (11, 14, and 8 days earlier, respectively) indicating that food abundance limits the initiation of molt. Along with interannual variation, these results indicate that photoperiod is not the sole cue for initiation of molt. 6. Both control and supplemented birds molted in sequence, starting with the body, followed by the crown 9 days later, and the face 11 days after the body. The presence of a sequence further suggests energetic limitation of molt or possibly a strategy to molt specific regions first to ensure completion or at an optimal time. 7. This study provides novel experimental evidence that food abundance can: i) limit pre-alternate molt timing and ii) limit molt timing in the wild. Food limitation of molt timing could allow earlier breeding or production of higher quality feathers, and thus cascade through other life history stages and affect reproductive success. These results indicate that food availability is a cue for molt initiation, possibly acting secondarily to photostimulation.

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Hyde County
Coastal North Carolina