Parental Quality and Egg Size as Components of Variation in Hatchling Size and Chick Survival in American Coots (Fuiica americana)
Variation in egg size and parental quality influence the survival of chicks in most bird species. The significance of each of these components varies depending on the developmental pattern of the species. Altricial birds hatch at a relatively early stage of development, and are completely dependent on parental care for thermoregulation, defense against predators, and food. Therefore, it is likely that parental quality would be more important than egg size in determining hatchling survival. On the other end of the continuum of avian development are birds with precocial young, which hatch at a more advanced stage of development and are able to leave the nest shortly after hatching. Thus, these birds rely less on their parents for protection and warmth leading to the hypothesis that egg size would be more important than parental quality in determining the survival of these hatchlings. We chose to study the semiprecocial American Coot, Fulica americana. These chicks are able to leave the nest soon after hatching, however, they depend exclusively on parents to provide them with food for the first two to three weeks after hatching. Hence, chick survival is most likely due to the effects of both egg size and parental performance. We found that larger eggs produce chicks that are structurally larger as well as heavier. We switched hatchlings among nests in order to examine the effects of pre-hatching (egg size, egg quality, and other maternal effects) versus post-hatching (parental care) attributes. In doing so, we hoped to investigate whether pre-hatching or post-hatching attributes were more important in determining the survival of coot chicks. Our results indicated that there was no difference in initial masses of chicks that survived to 7 days of age and those that died by age 7 days. This indicates that post-hatching attributes (parental performance) probably plays a significant role in the survival of coot hatchlings.
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