Zipf’s Slope

Investigating the southern residents’

repertoire with Information

Theory

Kenna Lehmann

Beam Reach Marine Science and Sustainability School - beamreach.org/071

Communication

• The passing of information from one individual (the sender) to another (the receiver)

Sender Receiver

Information

Communication Channels

• Different senses (i.e. sight, sound, smell)

• Different environments (i.e. the ocean, the forest, the savanna)

Background

• Orcas are highly social and vocal– Communication is key in maintaining social

interactions

• Call meanings have never been determined– No correlation between behavior and call-type

Questions

• What information do orcas send in their calls?

• How much information do orcas send in their calls?

• How is that information organized?

Information Theory• Quantitative way to analyze a

communication system

• As designed by Shannon and Weaver (1949) – Determines how a communication system is

internally organized

• Zipf’s slope: indication of a repertoire’s potential to contain information

Calculating Zipf’s slope

Zipf’s Slope

Balance between

Too diverse

Y=-.5+B

Too unified

Y=-1.5x+B

Methods

Additional recordings

Call Types

Ford (1991)

What?

• The southern residents’ repertoire has a Zipf’s slope that is steeper than optimum

• Decreased from 1979-1983 to 2006-2007

• Repertoire is too unified (i.e. repetition)

Why?

• Too much background noise in the communication channel?

• Contact calls?

• Have Soundwatch guidelines decreased boat noise in recent years?

Further Research

• Comparing different populations and species

• Use Shannon and Weaver’s Information Theory to evaluate the internal organization of the repertoire

Acknowledgments

John Burt for Syrinx, Scott and Val Veirs for Call Tutor and guidance, FHL computer team for helping with the many computer glitches, team VaTo, Leslie Veirs for the goodies, Mike for not crashing the boat (oh wait), my parents for obvious reasons, Shannon Fowler for the excellent feedback on my papers and life, Jason Wood for the support, feedback, brainstorming and putting up with us

And to my favorite whales: Liz, Heather, Elise, and WesFor the good times