Reproductive Effort Of Male And Female Killdeer (charadrius Vociferus) (michigan).

Abstract

The reproductive investment strategies of the sexes were analyzed for Killdeer (Charadrius vociferus), a monogamous plover. The investments of the sexes in reproductive (mating and parental) effort, were studied during 1983 near Ann Arbor and 1984-1985 at Houghton Lake, Michigan. Investments were measured in terms of time, energy, and risk-taking. Time-energy budgets were used to test the predictions that: (1) males invest more in mating effort (ME) than females; (2) females invest more in parental effort (PE) than males; (3) male and female cumulative energy expenditures in reproductive effort (RE) are equal; and (4) mate removal results in increased investment and lower reproductive success for the 'deserted' parent. Males' cumulative energy expenditures in RE were higher than females' over a successful nesting attempt. However, the early high PE by females, and the timing of nest failures, resulted in females investing more PE than males over the season. Similarly, male investment in ME was higher than female ME investment over the season. Over the breeding season males and females invested the same amount of energy in RE. Males approached predators closer, displayed more intensely, and remained on the nest longer during a predator approach than females. 'Risk-taking' by both sexes increased during incubation, peaked at hatching, and decreased as chicks developed. Responses varied with the predator species, the mode of predator approach, and the distance between the predators and the offspring. 'Deserted' parents were unable to raise offspring alone. However, males were able to hatch chicks, whereas females lost or abandoned their nests a few days after mate removal. Monogamy in killdeer may result from high nest failure rates, low reproductive success of uni-parental care, and the nature of parental care. The effect of nest failure on the relative investments of the sexes has been overlooked in the relationship between parental investment and mating systems.