Assimilation efficiency and growth of nestling insectivores

The efficiency of energy assimilation by Pacific Swallows Hirundo tahitica and Blue‐throated Bee‐eaters Merops viridis was measured in captive nestlings fed on their natural diets. Assimilation efficiency (AE) was 68% in Pacific Swallows, similar to published values for altricial nestlings, including other hirundines. AE was unusually low in Blue‐throated Bee‐eaters, conforming to results with the European Bee‐eater Merops apiaster , at around 57%. As expected, nestling growth was positively correlated with daily metabolized energy. Estimates of daily metabolized energy for captive reared nestlings, closely resembled estimates obtained for wild youngsters in an earlier study using different methods.