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When evaluating avian reproduction, life history theory examines the trade‐offs between parental effort, the number and size of offspring, and the rate of nestling development. The growth rates and body sizes of developing birds vary geographically and can diverge with both latitude and migratory strategy. In terms of offspring size, growth rate can deviate in nestlings of the same or similar species due to the correlated influences of weather events, predation pressure, food availability, number of nestmates and parental provisioning. Furthermore, a longer photoperiod for species nesting at higher latitudes increases the duration over which a nestling can be fed each day, and increased nestling provisioning has been positively correlated with growth rate. Whether the amount of time a bird is fed during development drives this variation in growth rate and morphology is unknown. By removing supplemental environmental stressors (e.g. weather, predation) and standardizing feeding rate and environment, we explored the influence of daily duration of nestling provisioning on dark‐eyed junco Junco hyemalis nestlings. We hand‐reared 65 chicks of a sedentary junco subspecies J. h. carolinensis under both their natural photoperiod and the longer photoperiod of a closely related migratory subspecies J. h. hyemalis and compared growth rate, mass, morphology and the amount of food consumed. Average growth rate, fasted mass, wing length and total daily food consumption were all greater in birds hand‐reared under the longer, more northern photoperiod treatment. These findings suggest that increased daily photoperiod at higher latitudes may allow for greater total food provisioning and thus may play a role in the ability of parents in compressed breeding seasons to produce high quality offspring. This points to a trade‐off between provisioning effort and nestling growth rate in lower latitude (shorter photoperiod) populations and points to an important role of developmental plasticity on growth rate and morphology.
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Plan ahead, or wing it? How storm-petrel parents adjust food delivery to young chicks
Abstract Parents must decide how to allocate energy gained from foraging between self and offspring. Storm-petrels (Procellariiformes: Hydrobatidae) are pelagic seabirds that travel hundreds of kilometers across multiple days before returning to the nesting burrow to feed a dependent chick. Parents return to the nest with food stored in the proventriculus, a portion of which is regurgitated to their offspring. As the chick grows, provisioning demands increase. However, it is unknown whether parents meet this increasing demand by (1) altering their foraging strategies to acquire more food or (2) allocating a greater proportion of their intake to the chick. We designed, validated, and implemented a new technology—the Burrow Scale Monitor—to measure Leach's storm-petrels (Hydrobates leucorhous) as they entered and exited the nesting burrow. We monitored breeding adults over the first 30 d of chick rearing to determine whether storm-petrel parents adjust their foraging intake to the age of the chick or simply adjust energy allocation at the nest. Food delivery increased with chick age, but this increase was driven to a much greater extent by parents delivering a greater proportion of their body mass as food (ie, a shift in parental allocation) rather than by adults adjusting their foraging strategy to match chick age. Only by measuring adult body mass on arrival and exit at the nesting burrow could we understand how parents adapt their provisioning strategy to the increasing demands of the growing chick.
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- PAR ID:
- 10648688
- Publisher / Repository:
- Oxford University Press
- Date Published:
- Journal Name:
- Behavioral Ecology
- Volume:
- 36
- Issue:
- 6
- ISSN:
- 1045-2249
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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