Overview

The Project 

Some Main Results

Description of Porpoise Sounds

The Porpoise Sonar System - Ear and Brain

Behaving Without Vision

Avoiding Invisible Surfaces

Exploring With Sound

Summary and Conclusion

Kellogg's work on sonar in porpoises was carried out mainly at a marine facility of Florida State University at Alligator Point on North Florida's gulf coast between 1952 and 1956. This research program was summarized in his book: W.N. Kellogg (1961) Porpoises and Sonar. Chicago: University of Chicago Press.

Shortly after his arrival at Florida State University in 1950, Kellogg began his well-known investigation of the sonar capacity of porpoises. This project was completed in 1956... In his investigation of the echolocating capacity of porpoises, Kellogg followed his characteristic ways. To begin with, his interest in porpoises was motivated by simple curiosity about how they were able to navigate so well. Believing that they used sonar, he set out to resolve the matter through experiments and careful observations. B&B, p.474

Robert Kohler, March 2002

Porpoise from Marineland being placed in lab pool at Alligator harbor.(circa 1953)

A unique perspective on the beginnings of the work and its progress is found in Robert Kohler's oral history. Kohler was the University engineer at Florida State and was a technical assistant to Winthrop Kellogg at the time of the porpoise study. Kohler describes how the idea to study porpoises came about while he and Kellogg were sailing by a school of porpoises one summer day. He recalled how Kellogg was intrigued at how the porpoises evaded the boat and objects in the water, and Kohler jokingly said, "Maybe they have sonar," and thus started their four-year study. Go to Kohler interview

 

The goals of the project were summarized in Porpoises and Sonar (1961):

"[The] [o]bject of the series of investigations. . . .has been to demonstrate the process of sonar or echo-ranging in the bottle nose dolphin, Tursiops truncates. [I] wanted to find out if a dolphin or porpoise could locate food objects, like fishes, by bouncing echoes off the fishes' bodies. [I] wanted to discover whether it could avoid submerged obstructions by using its ears alone. [Kellogg] wanted to learn if it could navigate at night or in turbid water without employing vision, tough, or any of the chemical senses. To do this under controlled conditions, [he] had to eliminate all of the other sensory avenues which these animals might conceivably make use of in such situations. The research program as a whole … has included both wild or free-swimming, as well as captive, porpoises." (Porpoises and Sonar, 1961, p. 151)

"[The] study of porpoise sonar has been divided into three main steps or stages. First, [I] analyzed the sound pulses which these animals emit for the purpose of echo-ranging. [I] sought to determine whether any of their water-borne noises possess the necessary temporal and acoustic characteristics for proper use as sonar signals. Second, [I] turned to the receiving side to find out if the echoes from porpoise sound pulses could be adequately decoded and analyzed. Lastly, [I] studied the porpoise in action by examining its ability to use its own sound signals in navigation and in orientation. This last stage has taken up the greater portion of the book" (Porpoises and Sonar, 1961, p. 152)

"The project. . . .was sponsored and supported by the Office of Naval Research (ONR) and the National Science Foundation(NSF). The ONR lent indispensable underwater sound gear, and the NSF gave financial aid in the form of substantial research grants. Additional funds for carrying on the work were obtained from the Psychology Department, the Oceanographic Institute and the research Council of Florida State University (Porpoises and Sonar, 1961, p.IX)."

 

"The underwater sounds which porpoises produce[d] most often [were] successive series of rapidly repeated clicks or pings. These noises [were] analyze[d] acoustically by several methods and in several places. [The noises]. . . .contained a wide band of both sonic and ultrasonic frequencies extending as high as 170,00 cycles per second. Echoes from such clicks have been measured and photographed." (Porpoises and Sonar , 1961, p.153)

Side and end views of the tympanic bulla and the periotic bones of the porpoise ear. The ossicles (not shown here) lie between these two bony parts. The cochlea and vestibular canals are in the periotic bone.

"Another way of eliminating vision which proved effective was to conduct tests during the night, when it was so dark 'you couldn't see your hand before your face.' Still a third method was to immerse invisible obstructions, like sheets of plate glass and transparent Plexiglas, and to see whether the animal could avoid colliding with them. (Porpoises and Sonar, 1961, p.153)."

"[I] learned. . . .porpoises are able to differentiate between food-fish of different sizes by listening to the echoes reflected from the fishes' bodies. This came to light in a discrimination experiment. In the tests which were made, the two fish to be distinguished not only had different reflecting areas, but they were also of different species. One of the fishes was distasteful or unpalatable to the porpoise, and it would reject this variety of fish even after it had one in its mouth. The other or "positive' food-fish was a species which was much sought after." (Porpoises and Sonar, 1961, p.155) 

The turbidity of the water acted somewhat like a one-way-vision screen. The experimenters above the water level could see sufficiently far beneath the surface to observe the porpoise's head and mouth, but the animal could not detect the target fishes in a horizontal direction. The difference between the absolute threshold for distance and the differential threshold-to-threshold of discrimination between the target fishes is also illustrated in this figure.

"In another situation, a pair of desirable or preferred food-fish were used as rewards. Each fish was now identical in size and visual appearance; yet the arrangement was such that one of the paired fishes was always offered behind an invisible sheet of plate glass. The remaining fish was readily available and could be taken and eaten by the animal. The glass was sometimes in front of the right-hand fish and sometimes in front of the left-hand fish. If a porpoise relied on vision in such a situation, it would certainly make some approaches to the glass. Yet, because a sheet of glass 'sounds different' from a small fish, no mistakes at all occurred in more than 200 trials (Porpoises and Sonar, 1961, p.155)."

Plan of the net experiment. A steel net or fence was stretched tightly across the porpoise pool beneath the water, dividing it into two sections. Two openings or doorways in the fence permitted the animals to swim from one section of the pool to the other. A heavy sheet of clear Plexiglas was used as a barrier to block one of the openings. An opaque plastic curtain, manipulated from the bank, was lowered between trials to cover both openings.

 

 

"During intensive work with two experimental subjects, many interesting discoveries came to light. [Kellogg] found, for one thing, that the noises of a splash upon the surface of the water inevitably triggered a series of porpoise sound pulses. The animals appeared to be "looking with their ears" to find out if some foreign object had entered the water. If a splash was made alone, without the immersion of a target, the sputtering signals stopped after a few seconds. When a splash was followed by the presence of some new object in the water, exploratory sound signals continued-presumably until the size and distance of the object had been determined (Porpoises and Sonar, 1961, p. 154)."

"Thirty-six sheet-metal poles were suspended over an enclosed area. These could be simultaneously lowered into the water by assistants who operated tackle from the shore. Only a limited space was allowed for movement between these submerged obstructions. Each pole gave off a bell-like ring when touched or struck, so that collisions were automatically registered on sound-recording tape even though they could not be seen. A few collisions occurred at first, but as soon as the [porpoises] got used to making the short and difficult turns required in this situation, the errors ceased. Even at night, there were no further collisions." (Porpoises and Sonar, 1961, p. 156)

 

General design of the outdoor "porpoise laboratory." The dimensions of the pool were 55 by 70 feet. Overhanging cables between rows of telephone poles to the east and west were used for supporting underwater apparatus or partitions. A small crane or hoist to the south permitted lowering of heavy acoustical equipment.

 

 

 

SUMMARY AND CONCLUSION

The major contribution of the Porpoise and Sonar (1961) project was not that porpoises made sounds, which had been recorded by the US Navy in the early 1940s, but what the sounds were used for. The findings were even viewed as "… have a bearing on national defense, as a means of improving Navy sonar or echo ranging of the porpoise is superior in many respects to the best that man has yet been able to develop …" (Porpoises and Sonar, p.152)."

In a second porpoise project carried out in California after Kellogg left Florida State University, he tested the visual and problem-solving capacities of porpoises above and below the water line. A summary of this work is found in Kellogg and Rice (1966) and in Benjamin & Bruce (1982, p. 475-478; see link)