(The New York Times)
MAY 9, 2012, 12:27 PM
Playing Tag With Dolphins
By TARA THEAN
Chicago Zoological Society/Sarasota Dolphin Research Program
A bottlenose dolphin pair surfacing for air in Sarasota Bay, Fla., wearing DTAGs that record their vocalizations. (Photo taken under National Marine Fisheries Service Scientific Research Permit No. 15543.)
Tara Thean, a biology major at Princeton University, writes from Sarasota Bay in Florida, where she is studying signature whistle development in wild bottlenose dolphins.
Monday, May 7
I saw my first dolphins at 8 a.m. on an overcast Monday morning in Sarasota Bay, Fla., just seven minutes after leaving the boat ramp near Mote Marine Laboratory. The dolphins, muscular creatures about two and a half meters long, were a mother-calf pair named Boxer and Box 1. They powered smoothly through the water with their sleek blue-gray bodies, staying close together as we watched from 50 meters away.
Few animals have had their life stories so closely documented as the dolphins in Sarasota Bay. There are people out here who could tell you about a particular dolphin's date of birth, list the sex of each of its calves and describe its behavioral ups and downs simply by looking at the nicks and notches on its fin. From time to time, a team of veterinarians and scientists from around the world work with the Chicago Zoological Society's Sarasota Dolphin Research Program to conduct health assessments and photo-identification surveys of the Sarasota dolphin community, gathering biological, behavioral, ecological and health data for use by field biologists, conservationists and veterinarians.
I am fortunate to be part of one such team this spring. I will write a senior thesis that focuses on bottlenose dolphins under the supervision of Laela Sayigh, a research specialist at the Woods Hole Oceanographic Institution. Laela has kindly allowed me to take part in this trip to help with data collection and to get some hands-on experience with the animals I will be thinking and writing about for the rest of my undergraduate career.
Our days in the field begin at 7:15 a.m. We set out in an outboard-powered vessel called Nai'a. We pack light, bringing only water, food and SPF 30 sunblock in anticipation of a 13-hour field day in the 85-degree weather of Sarasota Bay. While most of the 80 field researchers who join us out on the water are heavily involved with sample collections and dolphin examinations, I am part of a small subteam investigating signature whistles in bottlenose dolphins.
Bottlenose dolphins – so named because of their elongated jaws – have an extensive sound repertory consisting of whistles, burst-pulsed sounds and broadband clicks. Their most distinctive vocalization, however, is the signature whistle: a stereotyped acoustic signal that indicates the identity of the caller. This identity is encoded in a specific frequency modulation pattern that the dolphin learns as a calf and keeps throughout its life. Such distinctive calls provide a means for bottlenose dolphins to find one another, a particularly useful ability in the animals' large, fluid social networks. When separated from the others, dolphins emit signature whistles more than any other whistle type, which allows specialists to easily identify a particular dolphin's signature.
Sayigh and Janik 2010Spectrograms of three signature whistles from a 15-year-old female Sarasota Bay dolphin, recorded during brief capture-release events.
But there's still a lot we don't know about signature whistles. Part of the problem has to do with the logistics of recording sound. It is difficult, for example, to identify which dolphin makes a particular sound within a group whose members are all vocalizing at the same time.
Our job is to attach tags to several dolphins – we aim for three or four per day – that are programmed to stay on the animals for 24 hours. Called DTAGs, these devices are a welcome change to the dolphins from the older, suction-cup-mounted tags; they are comparatively small, and the animals can easily release the tags if they are at all bothered by them. The DTAGs record all vocalizations made by the tagged animal, with which we make spectrograms using special computer programs. Ideally, we'd like the tags to stay on for 24 hours to get acoustic information on each dolphin spanning an entire day and night.
After attaching the tags early in the day, we immediately begin "focal follows" of the tagged dolphins. Focal follows are a behavioral sampling technique in which researchers track individuals for extended periods of time to get data on spontaneous social behavior in animal groups. By following the dolphins at a safe distance in our boat and recording various behavioral indicators every three minutes, we obtain a comprehensive suite of behavioral data that we can later use with the whistle spectrograms to figure out what the animals are doing when they make particular sounds.
I talked to the researchers in my boat today about the different questions we all hope to answer about signature whistles. I'm interested in how dolphins learn these whistles — it's been suggested that they copy the whistles from other individuals and then tweak them slightly to make them their own, and I'm hoping to figure out which community members they select as their models. But things are always a bit hectic on the first day of fieldwork, with researchers who haven't been in the field for a while working out the kinks.
We didn't get as much data as we wanted today, as the DTAGs stayed on the dolphins for only about six hours. Tomorrow we will give these DTAGs another go — if they fall off prematurely again, we may order different ones to use in the later days of the trip.
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