Factors affecting intra- and inter-specific variations in the difference between alert distances and flight distances for birds in forested habitats

Abstract

Studies of escape from predators have usually focused on fleeing. We studied intra- and inter-specific variations in a previous level of decision-making during predator–prey encounters by determining the difference between the distance at which a predator is detected and the distance at which the prey flees from the predator (buffer distance). We measured buffer distances of four bird species (ground foragers) living in forested habitats (wooded recreational parks) to approaching humans. Buffer distances increased with group size and temperature, and this was probably related to dilution of the predation risk and a higher risk of heat stress, respectively. Buffer distances decreased with shrub and coniferous cover, probably because of increased visual obstruction, and increased with tree height, probably because of the increased security provided by taller trees. Grass cover increased buffer distances of wood pigeons (Columba palumbus) but decreased those of house sparrows (Passer domesticus) and magpies (Pica pica); this may be related to higher food availability, i.e., vegetation in grassy areas for wood pigeons and food left by humans in areas with bare ground for house sparrows and magpies. Buffer distances of blackbirds (Turdus merula) and house sparrows were greater in highly visited parks, which may be related to habituation. Finally, larger species showed greater buffer distances, landed farther away, used higher landing substrates (trees), and flew higher, probably because they need to ensure a certain margin of security from predators. Alternatively, the increased buffer distances of large species may be related to the increasing energy expenditure of flight. The buffer distance appears to be a good indicator of tolerance toward predators and (or) risk taken by prey after detecting predators.

The impact of disturbance from photographers on the Blue-crowned Laughingthrush (Garrulax courtoisi)

“…Many authors have investigated the responses of breeding birds to human disturbance, such as the energy costs of earlier flight initiation and vigilance (e.g., González et al 2006, Poudel et al 2015, changes in habitat use (e.g., Lafferty 2001, Fernández-Juricic et al 2002, Markovchick-Nicholls et al 2008, Lowe et al 2014, reduced parental care (e.g., Burger 1994, Verhulst et al 2001, Bautista et al 2004, Yasué and Dearden 2006, and decreased reproductive success (Safina andBurger 1983, Bailly et al 2016). Behavioral responses to human disturbance vary among species (Blumstein et al 2005), with, e.g., group-living species more likely to suffer from injuries during panic behavior (Carney and Sydeman 1999).…”

First to Flush: The Effects of Ambient Noise on Songbird Flight Initiation Distances and Implications for Human Experiences with Nature

“…Previous studies have determined that species identity, starting distance, individual body size, and vegetation cover are all important predictors of FID (Fernández-Juricic et al, 2002;Blumstein, 2003;Blumstein et al, 2003). The influence of noise on FID has been investigated in two nonavian systems.…”

To run or to fly: low cost versus low risk escape strategies in blackbirds

“…We used the blackbird (Turdus merula) as the model prey species due to its abundance and previous knowledge on its escape behaviour (Fernández-Juricic & Tellería, 2000;Fernández-Juricic et al, 2002;Blumstein et al, 2004). We used humans as model predators since human disturbance can cause anti-predator responses similar to those elicited by natural predators (Frid & Dill, 2002).…”

“…We used humans as model predators since human disturbance can cause anti-predator responses similar to those elicited by natural predators (Frid & Dill, 2002). Previous studies have corroborated that blackbirds responded to humans as if they were potential predators (e.g., Fernández-Juricic & Tellería, 2000;Fernández-Juricic et al, 2002;Blumstein et al, 2004).…”

“…Thus, individuals may delay escape (e.g., Fernández-Juricic et al, 2002), but they may also lower the magnitude of their escape response by using a low-cost strategy. Thus, we predicted that increasing numbers of conspecifics would increase the chances of escaping by running.…”