Effect of ambient noise on parent-offspring interactions in tree swallows

Many recent studies suggest that increased ambient noise can disrupt acoustic communication in animals and might ultimately decrease their reproductive success. Most of these studies have focused on long-distance signals used in mate attraction and territory defence, but close-range acoustic interactions between parents and offspring may also be disrupted by noise and are closely linked to reproductive success. To test the effect of noise on parent-offspring interactions, we experimentally applied white noise (65. dB SPL) to the nests of tree swallows, Tachycineta bicolor, when nestlings were 3-6 days old. At experimental nests, parents gave fewer provisioning calls, which are used to stimulate begging, but otherwise we detected no difference in provisioning behaviour between experimental and control nests. More nestlings begged for food at experimental nests, using calls that were higher in amplitude and minimum frequency, than at control nests. When we played back nestling begging calls during parental visits to stimulate higher feeding rates, parents increased their feeding rates at control nests, but not at experimental nests. Our results show that noise can alter parent-offspring interactions and interfere with parental responses to begging calls. Nestlings may be able to compensate for moderate increases in noise by enhancing the conspicuousness of their begging signal, although at higher noise levels these adjustments may prove ineffective or the extra begging effort may be physiologically costly.