Meeting Abstract
Growth rate can affect survival. For example, in tropical birds, growth rate is an important determinant of fledge timing. Fledging sooner limits time in the vulnerable nestling stage, and thus increases survival likelihood. Growth rate is influenced by environmental factors, such as quality of parental care, food availability, disease, and local weather conditions. However, few have investigated the possible effects of global climate phenomena on the growth rate of animals. The El Niño/southern Oscillation (ENSO) is one such global climate pattern characterized by warming of the tropical Pacific. The ENSO can affect primary production and population size of at least some species. We take the logical next step to determine if growth rate and survival is influenced by the ENSO. From 2007 to 2017 we measured the growth of 734 lance-tailed manakin (Chiroxiphia lanceolata) chicks throughout the nestling phase and estimated average yearly growth rate. We found that during years of higher El Niño activity nestlings grew significantly slower. Counterintuitively, more severe El Niño years correlated with drier conditions at our field site in south central Panama. We also found a significant negative correlation between El Niño intensity and the occurrence of insect-induced lesions. That is, during breeding seasons of heavier than average rain fall, nestlings grew faster, but developed sores more often, presumably because of increased populations of predatory insects in those years. Neither ENSO nor chick growth rates were related to chick recruitment. Enhanced growth rates in years of lower El Nino intensity are accompanied by a tradeoff from increased exposure to predatory insects, which may explain the lack of a relationship between growth rate and survival.
