Foraging Behavior of Nightingales (Luscinia Supergenus): An Experimental Study

Abstract

Abstract—Foraging techniques influence the morphological peculiarities and ecological specialization of species, also determining their organization in a community. The foraging behavior of forest ground insectivorous birds remains the least explored due to the difficulty of observing them in the wild. We studied the foraging behavior of four nightingale species in an outdoor aviary where they were given a choice of typical foraging substrates. Two categories of young birds took part in the experiment: hand-raised and wild birds. Five aspects of behavior were recorded: foraging intensity, structure of background activity, attack maneuvers, attack direction, and substrate preference. The coefficients for converting the noted activity into energy expenditure units were developed. The behavioral parameters, except for the intensity of foraging, were expressed as the proportion of total energy expenditure for a given behavioral aspect, reducing the variation of these parameters related to a change in activity. Three principal components explain more than three-quarters of the interspecific differences in individual behavioral parameters. The first component corresponds to the foraging intensity and ranks the species according to decreasing body mass. The second component distinguishes the tactics of the Siberian Rubythroat as complex exploration of dense vegetation thickets from the tactics of the Rufous-tailed Robin as detailed extensive ground surface exploration. The third component contrasts the tactics of the Bluethroat (alternation of moving, waiting, and long sally-hovers) to the tactics of the Siberian Blue Robin (intensive short aerial attacks). The species-specific foraging traits appear in young birds independently of the wildlife experience. While learning by doing, they increase the foraging intensity and strengthen specific behavioral traits. The type of substrate determined the foraging intensity and ratio of the expenditure for search, movement, and attacks. Foraging techniques and their direction are correlated with other behavioral aspects, but are partly determined by the preference of specific preys and their properties. Despite the well-marked distinctions, the foraging niches of the nightingales strongly overlap; i.e., each behavioral aspect of the species studied is dominated by basic, less specialized elements.