Applicability of Information Theory to the Quantification of Responses to Anthropogenic Noise by Southeast Alaskan Humpback Whales

Sean Hanser,Brenda McCowan,Laurance Doyle,J. Blue,Taylor Bucci,Christopher Chyba

doi:10.3390/entropy-e10020033

Sean Hanser, Brenda McCowan + Show 4 more

Open Access

https://doi.org/10.3390/entropy-e10020033

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Abstract

We assess the effectiveness of applying information theory to the characterization and quantification of the affects of anthropogenic vessel noise on humpback whale (Megaptera novaeangliae) vocal behavior in and around Glacier Bay, Alaska. Vessel noise has the potential to interfere with the complex vocal behavior of these humpback whales which could have direct consequences on their feeding behavior and thus ultimately on their health and reproduction. Humpback whale feeding calls recorded during conditions of high vessel-generated noise and lower levels of background noise are compared for differences in acoustic structure, use, and organization using information theoretic measures. We apply information theory in a self-referential manner (i.e., orders of entropy) to quantify the changes in signaling behavior. We then compare this with the reduction in channel capacity due to noise in Glacier Bay itself treating it as a (Gaussian) noisy channel. We find that high vessel noise is associated with an increase in the rate and repetitiveness of sequential use of feeding call types in our averaged sample of humpback whale vocalizations, indicating that vessel noise may be modifying the patterns of use of feeding calls by the endangered humpback whales in Southeast Alaska. The information theoretic approach suggested herein can make a reliable quantitative measure of such relationships and may also be adapted for wider application to many species where environmental noise is thought to be a problem.

Highlights

The effect of anthropogenic activities on wildlife health and reproduction has gained increasing attention in recent years [1]
To quantify how humpback whales may modify their vocal behavior in response to noise, we used recordings collected by Glacier Bay National Park Service biologists over the past 10 years on humpback whale vocalizations and associated noise from Glacier Bay and Icy Strait
We examined, using these quantitative techniques, the acoustic structure and patterns of use [27, 21, 22, 28, 29] of humpback whale feeding calls from various locations, each subjected to appreciable levels of intermittent vessel noise

Summary

Introduction

The effect of anthropogenic activities on wildlife health and reproduction has gained increasing attention in recent years [1]. The second-order (approximation to the) entropy measures the decrease in number of bits in the overall entropy of the signaling system by taking into account the amount of dependency (conditional probabilities) that exists between any two call types (i.e., di-gram structure in human languages) within sequences of calls in a repertoire. To quantify how humpback whales may modify their vocal behavior in response to noise, we used recordings collected by Glacier Bay National Park Service biologists over the past 10 years on humpback whale vocalizations and associated noise from Glacier Bay and Icy Strait We examined, using these quantitative techniques, the acoustic structure and patterns of use [27, 21, 22, 28, 29] of humpback whale feeding calls from various locations, each subjected to appreciable levels of intermittent vessel noise. We computed the information transmission rate decrease with increased noise—treating Glacier Bay itself as a noisy channel (and assuming that the vessel noise is Gaussian)—in order to compare this decrease in channel capacity with our measured decrease in humpback whale information transmission rates as measured for the zero, first, and second-order entropies during both low background noise and high vessel noise. (We were limited to the secondorder entropy due to our limited sample size; e.g., [21])

Materials and Methods for Humpback Whale Signal Collection

Quantifying Humpback Whale Vocal Responses to Boat Noise

Calculating Effects of Boat Noise on the Channel Capacity of Glacier Bay

Comparing Channel Capacity with Humpback Whale Signal Transmission Rate

Findings

Conclusions