Early development, recruitment and life history trajectory in long-lived birds

Lindström (in Trends Ecol Evol 14:343–347, 1999) synthesized knowledge about “early development and fitness in birds and mammals”, interesting tracks and challenges for future studies. Today, there is unambiguous evidence that Lindström’s first statement holds in long-lived birds: “It is obvious that adverse environmental conditions might have immediate effects […].” However, whether there are “long-term fitness consequences of conditions experienced during early development” (Lindström’s second statement) is unclear for long-lived birds. The extent to which the disadvantage of frail individuals at independence is expressed predominantly in terms of higher mortality and disappearance from the population before recruitment, or persists after recruitment, is still an open question. Due to the rarity of relevant data and the fact that most studies are retrospective, heterogeneity in methods and timescales hampers the identification of general patterns. Nevertheless, several studies have provided evidence of a relationship between early conditions and future reproductive parameters, or lifetime reproductive success. Evidence from large mammals suggests substantial long-term individual and population effects of early conditions, including trans-generational maternal effects. Evidence from short-lived birds also suggests long-term individual consequences, and maternal effects have been documented in long-lived ones. Despite logistical and financial difficulties inherent in long-term studies, they are the only way of addressing Lindström’s second statement. Existing long-term longitudinal datasets should be re-analyzed using recently developed capture–mark–recapture models handling state uncertainty and unobservable heterogeneity in populations. Statistical methods designed to estimate lifetime reproductive success or incorporate pedigree information in standard situations of studies of wild vertebrates with imperfect detection offer new opportunities to assess long-term fitness consequences of early development in long-lived birds.