Experimental Reduction of Hematocrit Affects Reproductive Performance in European Starlings, Sturnus Vulgaris

Given the function of hemoglobin and observed increases in hematocrit during periods of increased energetic demands, hematocrit and hemoglobin are assumed to be related to aerobic capacity. Reductions in hematocrit and hemoglobin during reproduction are similar in magnitude to increases associated with aerobically demanding activities and therefore we sought to investigate whether these reductions in hematology have consequences for reproductive performance. We analyzed associations between natural variation in hematology in free-living European starlings (Sturnus vulgaris) and reproductive performance. To test whether transient reductions in hematology during different stages of reproduction (egg production and late incubation/early chick rearing) affected measures of reproductive performance, we also manipulated hematology using phenylhydrazine (PHZ), which lyses red blood cells. To investigate effects of reductions of hematology during egg-laying, we treated females with PHZ or saline (control) upon completion of their unmanipulated first clutch and removed eggs to induce the production and rearing of a replacement clutch. To investigate effects of reductions of hematology during chick rearing, we treated females during incubation of the unmanipulated first clutch and then monitored the subsequent hatching and rearing of the clutch. Individuals with higher hematocrit and hemoglobin initiated nesting earlier.  Furthermore, higher hemoglobin levels during incubation were associated with a greater number of chicks fledged.  PHZ treatment prior to egg production resulted in a significant delay in the laying of replacement clutches, but had no effect on provisioning rate or the size or number of chicks fledged. PHZ treatment during incubation and early chick rearing resulted in decreased hatchling mass in all years and a decrease in the size and number of fledglings in one of two years. The year that the effect of PHZ was observed appeared to be a particularly difficult year, since hatchling mass, brood size at hatching and at fledging were low among control females compared to other years. Our results suggest that a reduction in hematology during reproduction can be functionally significant, but that these costs are context-dependent. &nbsp

Prolactin, body condition and the cost of good parenting: an interyear study in a long-lived seabird, Gould\u27s Petrel (Pterodroma leucoptera)

1. The pituitary hormone prolactin is thought to play an important role in the promotion of parental care in birds and mammals. The level of care parents provide is, however, likely to be influenced by additional factors, such as their physiological condition at the time of breeding.2. We examined relationships between parental body condition, plasma prolactin levels and reproductive performance in Gould\u27s Petrels (Pterodroma leucoptera), a long-lived seabird. We predicted that parental body condition would correlate positively with both prolactin level and parenting intensity, as measured by the quality of the chick they produced. We also examined the effects of parenting intensity on parental body condition and reproductive success in the subsequent breeding season.3. Body condition of male parents positively correlated with prolactin levels at the start of their second protracted incubation bout. The body condition of both parents correlated positively with the body condition of their chick at its peak mass. However, producing a good-quality chick did not negatively affect parental body condition or reproductive success the following year.4. These results suggest that prolactin reinforces parental behaviour in parents in good body condition, which facilitates production of good-quality chicks. Moreover, good-quality parents consistently produce good-quality chicks with no apparent trade-off to their physical condition.<br /