Responses to terrestrial nest predators by endemic and introduced Hawaiian birds

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.

Phenotypic divergence of traits that mediate antagonistic and mutualistic interactions between island and continental populations of the tropical plant, Tribulus cistoides (Zygophyllaceae)

“…Islands typically have fewer native mammalian herbivores, favoring birds and reptiles with high dispersal capacity over water (Burns, 2019). This discrepancy can lead to the evolutionary loss of antiherbivore defenses in plants (Baier & Hoekstra, 2019;Cummins et al, 2020). For example, spines largely evolve as protection against vertebrate herbivores, as in the case of the Island Bush Poppy (Dendromecon rigida harfordii) on the Island of Santa Cruz, California, where these plants evolved reduced spines due to a historical lack of herbivores (Bowen & Vuren, 1997).…”