Geology topics

Keith C. Hamer

Publications and source records attributed to Keith C. Hamer.

3 recordsLinked to original sources

USGS2009

Flexibility in the parental effort of an Arctic-breeding seabird

Parental investment strategies are considered to represent a trade-off between the benefits of investment in current offspring and costs to future reproduction. Due to their high residual reproductive value, long-lived organisms are predicted to be more reluctant to increase parental effort. 2. We tested the hypothesis that breeding little auks (Alle alle) have a fixed level of reproductive investment, and thus reduce parental effort when costs associated with reproduction increase. 3. To test this hypothesis we experimentally increased the flight costs of breeding little auks via feather clipping. In 2005 we examined changes in the condition of manipulated parents, of the mates of manipulated parents, and of their chick as direct measures of change in parental resource allocation between self-maintenance and current reproduction. In 2007 we increased sample sizes to determine whether there was a physiological cost (elevated corticosterone, CORT) associated with the manipulation. 4. We found that: (i) clipped birds and their mates lost more body mass than controls, but there was no difference in mass loss between members of a pair; (ii) clipped birds had higher CORT levels than control birds; (iii) there were no inter-annual differences in body mass and CORT levels between clipped individuals and their mates at recapture, and (iv) chicks with a clipped parent had lower peak and fledging mass, and higher CORT levels than control chicks in both years. 5. Contrary to our hypothesis, the reduction in body mass of partners to clipped birds suggests that little auks can increase parental effort to some extent. Nonetheless, the lower fledging mass and higher CORT of chicks with a clipped parent indicates provisioning rates may not have been fully maintained. 6. As predicted by life-history theory, there may be a threshold to the additional reproductive costs breeders will accept, with parents prioritizing self-maintenance over increased provisioning effort when foraging costs become too high. ?? 2008 British Ecological Society.

Functional Ecology↗

USGS2009

Impacts of experimentally increased foraging effort on the family: offspring sex matters

We examined how short-term impacts of experimentally increased foraging effort by one parent reverberate around the family in a monomorphic seabird (little auk, Alle alle), and whether these effects depend on offspring sex. In many species, more effort is required to rear sons successfully than daughters. However, undernourishment may have stronger adverse consequences for male offspring, which could result in a lower fitness benefit of additional parental effort when rearing a son. We tested two alternative hypotheses concerning the responses of partners to handicapping parents via feather clipping: partners rearing a son are (1) more willing or able to compensate for the reduced contribution of their mate, or (2) less willing or able to compensate, compared to those rearing a daughter. Hypothesis 1 predicts that sons will be no more adversely affected than daughters, and the impact on parents will be greater when rearing a son. Hypothesis 2 predicts that sons will be more adversely affected than daughters, and parents raising a son less affected. Although experimental chicks of both sexes fledged in poorer condition than controls, sons attained higher mass and more rapid growth than daughters in both groups. Clipped parents lost a similar proportion of their initial mass regardless of chick sex, whereas partners of clipped birds lost more mass when rearing a son. These results support hypothesis 1: impacts of increased foraging effort by one parent were felt by offspring, regardless of their sex, and by the partners of manipulated birds, particularly when the offspring was male. ?? 2009 The Association for the Study of Animal Behaviour.

Animal Behaviour↗

USGS2003

Breeding ecology of Horned Puffins ( Fratercula corniculata ) in Alaska: annual variation and effects of El Niño

Both within and among seabird species, different aspects of breeding biology may respond to changes in prey availability in distinct ways, and the identification of species-specific breeding parameters that are sensitive to food availability is useful for monitoring purposes. We present data from a 5-year study (19951999) of the breeding ecology of Horned Puffins ( Fratercula corniculata ) in Alaska. The El Niño Southern Oscillation event of 19971998 provided an opportunity to examine the sensitivity of various breeding parameters to a reduction in prey availability caused by the anomalous oceanographic conditions of 1998. Horned Puffins were able to maintain high fledging success (8397%) over the 5 years of the study, despite the poor local feeding conditions in 1998. The rate of increase in chick mass was lowest in 1998, and evidence suggests that chicks also fledged at the youngest ages in that year. The impacts of reduced food availability on growth varied among body structures, suggesting differential allocation of energy and nutrients. There was no variation among years in either chick diet or the mass of food loads delivered by adults. We suggest that rates of chick growth, specifically mass increase, may be a good parameter to measure for use in monitoring Horned Puffins.

Canadian Journal of Zoology↗