Marine Mammal Biology 1

Lab Exercises

 

BEHAVIORAL OBSERVATION OF SEALS

Harbor seals, Phoca vitulina, are commonly found along the coast of New England. At low tide, harbor seals 'haul out' on intertidal ledges to rest and interact with both conspecifics, and members of a sympatric species, the gray seal (Halichoerus grypus). This lab is designed to introduce you to these species, and an example of the techniques used to study the animal's behavior.

The study of animal behavior has changed substantially over the past 50 years. A significant development in behavioral studies was the ethogram, a catalogue of all possible behaviors of the animal. Thus, an animal's complex repertoire of behavior can be theoretically broken down into subunits. Such subunits may be discrete or continuous, graded or non-graded (grading is a measure of magnitude), and may or may not be part of a sequence that is predictable or non-predictable.

We will access an intertidal ledge called Half-Tide Ledges by boat. We will time our trip to coincide with low-tide, and we will anchor at a set distance from the ledge to avoid disturbing the colony. This set of ledges is home to both harbor and gray seals. We will perform our observations from the boat. As a word of caution, it will likely be cold, and probably wet. Dress appropriately!

Developing an ethogram requires hundreds to thousands of hours of observation of many individuals (to account for individual variability). In this lab we will use the focal animal technique to begin such a process. In this application of the focal animal technique a pair of observers will choose an individual animal and observe it for a period of 90 minutes. For the first 30 minutes you will watch the animal to become familiar with its movements and interactions. During this period you should unambiguously describe the entire scope of the animal's behavior (even sleep!). Construct a chart and shorthand for describing these behaviors.

For the following 60 minutes, you should watch the animal for performances of those behaviors, counting their frequency and duration. Watching animals for extended periods of time can be extremely tiring and may lead to errors. For this reason members of an observation pair should alternate between observation and notetaking. This is one reason why it is important to decide upon an unambiguous description of the behaviors you are observing, since at least two different observers will be contributing to the data set.

Back on dry land, you should use your newly discovered skills in Excel (!) to graphically display your findings, and discuss the possible motivations behind the behaviors you observed (agonistic, courtship, play, feeding, grooming, etc.).