Extended parental care reduces subsequent productivity but not lifetime reproductive success in a long-lived raptor

<jats:p>Organisms need to balance life-history decisions that can affect fitness parameters in different directions. In iteroparous animals, a typical tradeoff revolves around investments into reproduction, where extended parental care benefits offspring, but imposes costs for parents’ future reproduction. However, whether extended parental care results in greater lifetime reproductive success is poorly understood. We quantified the fitness costs and benefits of parental care duration in a long-lived raptor, the Golden Eagle (Aquila chrysaetos), and simulated lifetime reproductive success for two contrasting scenarios. Juvenile eagles (n = 65) were GPS-tracked to determine parental care duration in a dense population in the European Alps. We then estimated the effect of parental care duration on juvenile survival probability, and on productivity of parents in the following year. We found that parental care duration ranged from 16 to 260 days and had no detectable effect on the survival of juvenile birds. However, the probability of raising offspring in the following year decreased from 20% to 8% for 3.5 additional months of parental care. Parents with either long or short care duration had on average a similar number (median: 5, range 1-9) of offspring surviving to recruitment age over their simulated reproductive lifespan. We therefore conclude that extended parental care durations are a compensation mechanism to ensure sufficiently high survival probability of offspring. In dense populations with overall low productivity the cost of a missed reproductive opportunity imposed by extended parental care is offset by the increased reproductive output after a year without breeding attempt. Ultimately, neither consistently long nor short parental care durations predictably increase lifetime reproductive success. This study therefore highlights that strong annual reproductive trade offs do not necessarily scale up to lifetime fitness differences, which facilitates the maintenance of diverse reproductive strategies.</jats:p>