Abstract
Birds free from nest predators for long periods may either lose the ability to recognize and respond to predators or retain antipredator responses if they are not too costly. How these alternate scenarios play out has rarely been investigated in an avian community whose members have different evolutionary histories. We presented models of two nest predators (rat and snake) and a negative control (tree branch) to birds on Hawaiʻi Island. Endemic Hawaiian birds evolved in the absence of terrestrial predators until rats were introduced approximately 1,000 years ago. Introduced birds evolved with diverse predator communities including mammals and snakes, but since their introduction onto the island approximately one century ago have been free from snake predation. We found that (a) endemic and introduced birds had higher agitation scores toward the rat model compared with the branch, and (b) none of the endemic birds reacted to the snake model, while one introduced bird, the Red‐billed Leiothrix (Leiothrix lutea), reacted as strongly to the snake as to the rat. Overall, endemic and introduced birds differ in their response to predators, but some endemic birds have the capacity to recognize and respond to introduced rats, and one introduced bird species retained recognition of snake predators from which they had been free for nearly a century, while another apparently lost that ability. Our results indicate that the retention or loss of predator recognition by introduced and endemic island birds is variable, shaped by each species' unique history, ecology, and the potential interplay of genetic drift, and that endemic Hawaiian birds could be especially vulnerable to introduced snake predators.
Highlights
Nest predation is the main cause of nest failure and is one of the main drivers of life-history traits and parental care behaviors in birds (Martin, 1995, 2015)
The two introduced bird species we studied exhibited strikingly different responses to the snake model, each providing responses more consistent with different hypotheses for the maintenance or loss of antipredator behaviors
Because Red-billed Leiothrix have experienced continuous threats from small mammal predators both in their natural range and after introduction to Hawai‘i, the multipredator hypothesis predicts they would retain recognition and responses to snakes, another climbing, terrestrial predator, even after living in Hawaii without snakes for over 90 years. Both predators were terrestrial, and our results suggest that recognition and response to snake predators in Red-billed Leiothrix may be innately linked to behavioral responses toward small mammalian predators
Summary
Nest predation is the main cause of nest failure and is one of the main drivers of life-history traits and parental care behaviors in birds (Martin, 1995, 2015). Hawaiian forest bird communities, composed of native endemic and recently introduced non-native species, offer an opportunity to experimentally study predator recognition and response in a community of birds with different evolutionary histories, on islands that were initially free of terrestrial predators and subsequently experienced introductions of additional predator types (i.e., mammalian predators). New Zealand passerine species have shown recognition and response toward introduced mammalian predators (Jamieson & Ludwig, 2012; Massaro, Starling-Windhof, Briskie, & Martin, 2008; White, 2014) in spite of having evolved in the absence of mammalian predators, and O‘ahuElepaio (Chasiempis ibidis) have shifted their nesting behavior in response to heavy rat predation (Vanderwerf, 2012) Under this hypothesis, endemic bird species would respond to rat models but would not generalize their recognition to another taxonomic group (e.g., reptiles; Ferrari, Gonzalo, Messier, & Chivers, 2007; Griffin, Evans, & Blumstein, 2001). Understanding the patterns of predator responses in endemic and introduced birds with differing evolutionary histories is important in light of the increasing rate of species introductions around the world and the threatened and endangered conservation status of many endemic island birds (Seebens et al, 2017)
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