When Leach's Storm-Petrel Parents Were Handicapped by Having Their Wing

When Leach's storm-petrel parents were handicapped by having their wing span shortened, they passed the increased reproductive costs to their offspring and maintained their own nutritional condition. In contrast, when starling or flycatcher parents were handicapped in a way that increased their reproductive costs, they bore at least part of the increased costs themselves and continued to allocate nearly the same amount of resources to their chicks. Given an important difference between the petrels and the starlings and flycatchers, these results most directly support the idea that a parent's allocation of resources is influenced by the

A) certainty of paternity.
B) gender of the offspring.
C) life span of the individuals.
D) all of the above.