Date of Award

2018

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Biology

Abstract

It is crucial for all prey species to possess the ability to precisely detect an incoming attack. For birds, vision is probably the main sensory mode in predator detection, but other senses are likely to be involved. In particular, auditory detection and recognition of predators in birds is largely unstudied. I thus evaluated the ability of wintering sparrows to detect attack based only on the non-vocal, scary sounds” of predators, thus focusing on a single sensory modality. My study species were emberizid sparrows, focusing on dark-eyed juncos ( Junco hyemalis ) feeding in mixed flocks with American tree sparrow ( Spizella arborea) and White-throated sparrow ( Zonotrichia albicollis ). I exposed foraging flocks to non-vocal playbacks of departure wingbeats (flight sounds) of other passerines (juncos and chickadees), red-tailed hawks ( Buteo jamaicensis ), and sharp-shinned hawks ( Accipter striatus ). Playbacks of approaching footsteps of a potential terrestrial threat (dogs) were also used. All responses were video recorded for analysis. Behavioral responses were measured mainly in terms of the proportion of a given flock that flushed to cover, or became highly vigilant. Sparrows were responsive to all of the wingbeat stimuli, especially when played at a relatively loud volume. Hawk wingbeat sequences were, however, the most evocative stimuli in producing immediate flushes to cover or general alertness, especially when comparing stimuli that were played at low volume. The sparrows' response to an approaching terrestrial stimulus often involved an extended alert posture, or jumping up onto perches for a better view, reactions never seen to the wingbeat stimuli (and likely maladaptive during a hawk attack). Thus, the results of these experiments suggest that these wintering sparrows are able to distinguish wingbeats from smaller birds from those of hawks, and that they can differentiate the auditory approach of terrestrial threats from aerial threats. Other experiments were performed that examined the salient features of the most threatening stimulus, sharp-shinned hawk wingbeats, to evaluate what these sparrows find most informational from the sounds of a predator. A single hawk wingbeat can elicit flushes to cover, but full reactions require 2 or 3 hawk wingbeats in their natural cadence. Removing the low-frequency portion of a hawk wingbeat, in a range presumably not heard well by these sparrows (under 2 kHz), rendered the hawk wingbeat stimuli much less salient to the sparrows; the full range of frequencies in a hawk wingbeat appears to be important. These emberizid sparrows clearly have the ability to sense incoming attacks, and make some assessment of the relative risks involved, using only their sense of hearing.

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