Dominance Hierarchy of Auditory Spatial Cues in Barn Owls
Background: Barn owls integrate spatial information across frequency channels to localize sounds in space.
Methodology/Principal Findings: We presented barn owls with synchronous sounds that contained different bands of frequencies (3-5 kHz and 7-9 kHz) from different locations in space. When the owls were confronted with the conflicting localization cues from two synchronous sounds of equal level, their orienting responses were dominated by one of the sounds: they oriented toward the location of the low frequency sound when the sources were separated in azimuth; in contrast, they oriented toward the location of the high frequency sound when the sources were separated in elevation. We identified neural correlates of this behavioral effect in the optic tectum (OT, superior colliculus in mammals), which contains a map of auditory space and is involved in generating orienting movements to sounds. We found that low frequency cues dominate the representation of sound azimuth in the OT space map, whereas high frequency cues dominate the representation of sound elevation.
Conclusions/Significance: We argue that the dominance hierarchy of localization cues reflects several factors: 1) the relative amplitude of the sound providing the cue, 2) the resolution with which the auditory system measures the value of a cue, and 3) the spatial ambiguity in interpreting the cue. These same factors may contribute to the relative weighting of sound localization cues in other species, including humans.
Competing Interests: The authors have declared that no competing interests exist.
Funding This work was supported by the National Institutes of Health (NIH) and National Science Foundation (NSF) graduate research fellowship. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.
Contacts:Eric I. KnudsenStanford University Medical Centereknudsen@stanford.edu
Citation: Witten IB, Knudsen PF, Knudsen EI (2010) A Dominance Hierarchy of Auditory Spatial Cues in Barn Owls. PLoS ONE 5(4): e10396. doi:10.1371/journal.pone.0010396
PLEASE LINK TO THE SCIENTIFIC ARTICLE IN ONLINE VERSIONS OF YOUR REPORT (URL goes live after the embargo ends): http://dx.plos.org/10.1371/journal.pone.0010396
FOR A PRESS-ONLY PREVIEW OF THE FULL ARTICLE, VISIT THE FOLLOWING URL: http://www.plos.org/press/pone-05-04-witten.pdf
IMAGE AVAILABLE AT THE FOLLOWING URL: http://www.plos.org/press/pone-05-04-witten.jpg [Please credit Barn owl (Tyto alba). Photo by Anne Knudsen supplemental photo to PLoS ONE article e10396]
A Currency for Offsetting Energy Development Impacts: Horse-Trading Sage-Grouse on the Open Market
Background: Biodiversity offsets provide a mechanism to compensate for unavoidable damages from new energy development as the U.S. increases its domestic production. Proponents argue that offsets provide a partial solution for funding conservation while opponents contend the practice is flawed because offsets are negotiated without the science necessary to backup resulting decisions. Missing in negotiations is a biologically-based currency for estimating sufficiency of offsets and a framework for applying proceeds to maximize conservation benefits.
Methodology/Principal Findings: Here we quantify a common currency for offsets for greater sage-grouse (Centrocercus urophasianus) by estimating number of impacted birds at 4 levels of development commonly permitted. Impacts were indiscernible at 1-12 wells per 32.2 km2. Above this threshold lek losses were 2-5 times greater inside than outside of development and bird abundance at remaining leks declined by 232 to 277%. Findings reiterated the importance of timelags as evidenced by greater impacts 4 years after initial development. Clustering well locations enabled a few small leks to remain active inside of developments.
Conclusions/Significance: Documented impacts relative to development intensity can be used to forecast biological tradeoffs of newly proposed or ongoing developments, and when drilling is approved, anticipated bird declines form the biological currency for negotiating offsets. Monetary costs for offsets will be determined by true conservation cost to mitigate risks such as sagebrush tillage to other populations of equal or greater number. If this information is blended with landscape level conservation planning, the mitigation hierarchy can be improved by steering planned developments away from conservation priorities, ensuring compensatory mitigation projects deliver a higher return for conservation that equate to an equal number of birds in the highest priority areas, provide on-site mitigation recommendations, and provide a biologically based cost for mitigating unavoidable impacts.
Contacts:Kevin E. DohertyNational Audubon Society Sciencekdoherty@audubon.org
Citation: Doherty KE, Naugle DE, Evans JS (2010) A Currency for Offsetting Energy Development Impacts: Horse-Trading Sage-Grouse on the Open Market. PLoS ONE 5(4): e10339. doi:10.1371/journal.pone.0010339
PLEASE LINK TO THE SCIENTIFIC ARTICLE IN ONLINE VERSIONS OF YOUR REPORT (URL goes live after the embargo ends): http://dx.plos.org/10.1371/journal.pone.0010339
FOR A PRESS-ONLY PREVIEW OF THE FULL ARTICLE, VISIT THE FOLLOWING URL: http://www.plos.org/press/pone-05-04-doherty.pdf
Source: Public Library of Science