A northern saw-whet owl in mid-flight. Credits: Buffalo Bill Center of the West
An occasional stroll through an urban forest or a developed landscape may leave one finding a cote of doves, thick vegetation, a family of hikers, and…heavy machinery? As a result of the advent of wide-spread geo-commercialism, many young entrepreneurs are looking to the forests for a quick return on investment. Many long-standing, unprotected forests are now plagued with bulldozers and dump trucks, all with one purpose: to exploit the land in the name of capitalism. Deforestation is now being conducted at an alarming rate; according to the world wildlife foundation, nearly 58 thousand square miles of forest are lost each year. With the introduction of heavy machinery, comes also the boisterous noise.
Hunting behavior, an innate process, is common amongst all walks of life, from lions to fish. Interestingly, many organisms have altered their hunting strategies to best fit their particular environment and attributes. For example, northern saw-whet owls primarily use auditory cues to hunt, due to the common inconspicuousness of their prey. This environmental necessity has allowed the owl auditory system to evolve for efficiency. Although northern saw-whet owls have developed an acute auditory system, how has the advent of anthropogenic noise in forest environments affected hunting behavior? A study by Mason et al., found that intense anthropogenic noise has the capacity to greatly alter hunting strategy and efficiency for acoustically specialized organisms, and the effects can reverberate throughout the ecosystem.
To understand how anthropogenic noise affected hunting behavior, the study investigated two fundamental hypotheses: (1) the dose-response hypothesis – hunting defects may increase with increasing noise, and (2) the threshold hypothesis – high noise levels may impair hunting or have no impact. The owls were presented with mice in two randomly chosen noisy environments ( 61-73 DBA and 46-55 DBA). Sound speakers produced an even sound field and the hunting process was recorded and further analyzed.
Mason and his colleagues found that there was no relationship between noise level and mouse movement. In addition, they found that the only hypothesis that was supported by the data was the dose-response hypothesis. Lastly, reaffirming the dose-response hypothesis, the researchers found that the probability of an owl detecting a mouse during an experimental trial decreased by 11% for each decibel increase in noise, and the probability of a strike decreased by 5% for each decibel increase in noise.
The inverse relationship between increasing decibels and the probability of detection, strike, and success. Credits: J. Tate Mason.
What significance does this experiment offer the general sensory ecology community? The experimental data supported the dose-response hypothesis that states that there is an inverse relationship between detecting, striking, and hunting prey and an increase in noise level. Although we are unable to prove the dose-response hypothesis, were are unable to reject it as a plausible explanation of this phenomenon. On a more general scale, the experiment did shed light on the complexity of the owl auditory sensory system and its role in hunting behavior and overall organism survival. The study sets up the framework for additional research in the quantification of saw-whet owl hearing ability. Finally, the study speaks volumes on the effects of anthropogenic noise on overall organism survival and should be used to support animal preservation grass-roots efforts and initiatives.
Reference:
Mason, J. Tate., McClure, Christopher J.W., Barber, Jesse R. 2016. “Anthropogenic Noise Impairs Owl Hunting Behavior.” Biological Conservation, vol. 199, pp. 29–32.
