Strategies of the Cooperatively Breeding Noisy Miner to Reduce Nest Predation

Abstract

Nest predators reduce the reproductive success of passerines and may also threaten the safety of adult breeders. This paper investigates potential strategies used by cooperatively breeding Noisy Miners Manorina melanocephala at a site in south-east Queensland to reduce the risk to their nests. First, nearly twice as many nests were built from June to September as from October to January. Conversely, the availability of insects needed to feed chicks was known to be higher in the warmer months. Predation risk was probably driving the timing of breeding, because early broods were significantly less likely to be preyed upon than were those built later in the year. Second, low nests (less than 2.5 m high) were more likely to be successful than nests built at heights of over 4 m. Low nests are less visible and accessible to raptors. No other measures of nest concealment or accessibility were linked with nest success. However, early nests were significantly better concealed than late nests. Noisy Miner nests are probably fairly obvious to diurnal predators because of the activity of many visitors around them, and the loud begging calls of nestlings. Finally, the number of visitors to a nest was not correlated with the fate of that nest. In conclusion, there was no single strategy for reducing the risk to noisy miner nests of predation. This was probably due to the diverse taxonomic range of potential nest predators at the study site.