Traffic noise correlates with calling time but not spatial distribution in the threatened poison frog Andinobates bombetes

Acoustically communicating species have evolved adaptations that allow them to transmit information and overcome signal masking where their habitat is disturbed by anthropogenic noise. To investigate whether calling behaviour or spatial distribution is related to road traffic noise we studied the poison frog Andinobates bombetes in a mid-elevation forest remnant that has been exposed to heavy traffic noise throughout more than four decades. To test whether frogs avoid call during noise episodes generated by passing trucks, we compared background noise levels between calling and non-calling times. To test whether traffic noise is correlated with frogs spatial distribution, we measured frog abundance, ambient noise, and environmental covariates throughout a set of 24 sampling plots between 15 and 300 m from two forest edges, one bordered by the road and another one by an agricultural field. Frogs called more often when traffic noise level was lower. Frogs abundance was only marginally correlated with distance to noisy edges but was predictable from the abundance of bromeliad tanks, an alleged limiting resource for their reproduction. Apparently, to avoid calling during episodes with higher noise level allowed frogs to reduce the detrimental masking effects of anthropogenic noise; if so, it would explain why frog distribution is poorly correlated with distance to the noisy road.

Affiliations: 1: Department of Biological Sciences, Universidad de los Andes, Carrera 1a #18A-10, Bogotá, Colombia