Research Perspective on Biological Science Vol. 12

Nest predation is the primary source of reproductive failure in birds and a major driver of avian breeding strategies. In some cases, minimising predation risk has led certain species to exploit the nest-defence behaviour of others. In these protective nesting associations, a passive defender species benefits from the aggressive nest defence of a protector species, which may deter or kill nest predators while defending its own nest or territory.

Breeding birds show considerable behavioural flexibility in assessing and responding to predation risk. Such flexibility requires that birds can evaluate local predation pressure, either through direct encounters with predators or by interpreting indirect cues such as prey abundance. Most documented protective associations occur in Arctic and northern regions, highlighting the need to determine their broader geographical extent. It remains unclear whether these associations are genetically encoded or culturally learned. Such strategies are expected to persist through evolutionary time if they confer measurable fitness benefits, particularly reduced nest predation. In this review, we focus on protective breeding associations involving owls, as well as certain raptors such as goshawks that frequently live in close proximity to several owl species. We then examine the functional link between predation on mesopredators and the resulting protection of small prey species, including songbirds. Finally, we address nest-site competition and its potential connections to interspecific interactions.