Undergraduate Honors Theses

Thesis Defended

Spring 2019

Document Type

Thesis

Type of Thesis

Departmental Honors

Department

Ecology and Evolutionary Biology

First Advisor

Dr. Andrew Martin

Second Advisor

Dr. Barbara Demmig-Adams

Abstract

Vocalization-based communication networks have been observed in multiple animal taxa. Many territorial animals in these communication networks tend to act differentially towards their neighbors compared to farther-removed strangers given competitive pressure in habitats. My study investigated communication among rufous-and-white wrens (Thryophilus rufalbus), and whether this involves greater aggression towards neighbors or towards strangers. T. rufalbus vocally defend territories year-round and have been shown to exhibit ability to discriminate between vocalizations of neighbors versus strangers (neighbor-stranger discrimination, NSD). I quantified whether T. rufalbus demonstrates different levels of aggression upon hearing played-back vocalizations from close-by neighbors, neighbors of adjacent neighbors, and most distant strangers. Multiple measured parameters exhibited such a gradient of aggression in a population of T. rufalbus in Monteverde, Costa Rica, particularly time spent vocalizing and number of songs performed while defending. Response intensity increased for both of the latter parameters from strangers to neighbor-neighbors and to direct neighbors. Other variables that increased, albeit less significantly, in the same direction (from strangers to neighbor-neighbors to neighbors), included bandwidth and range between minimum and maximum frequencies of vocalizations. My study thus demonstrates a gradient of aggression in defensive behaviors of T. rufalbus that is consistent with what has been termed the nasty neighbor effect of more aggressive responses to simulations of intrusions by neighbors compared to strangers. This gradient of aggression may involve eaves-dropping behavior (listening to the interactions of other individuals) as described in other species of wren that frequently listen to and identify vocalizations of individuals of the same species more than a territory away.

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