When passive nest defence is active: support of the leave early and avoid detection hypothesis in a plover

Abstract

Leaving the nest early to avoid detection by an approaching predator is an often-cited form of nest defence among ground-nesting birds, yet has rarely been quantitatively demonstrated. During the breeding season, we recorded Flight-initiation Distances (FIDs) of incubating, off-duty and non-breeding Hooded Plovers Thinornis cucuallatus cucuallatus in Victoria, Australia. Hooded Plovers exhibited longer FIDs when incubating compared with when off-duty or non-breeding birds (the latter two categories had similar FIDs). Our study supports the Leave Early to Avoid Detection (LEAD) hypothesis, and demonstrates that so-called ‘passive’ defence is in fact an active decision by the incubator to leave nests at distances which exceed those at which birds without nests or off-duty commence escape.