All essays were graded anonymously (by covering the name at the top of the sheet).

Each question was graded separately.

Scores are on the back of each sheet.

The maximal score for each question was 10 points. To receive 10 points an essay did not have to include all the information we discussed on the topic, but it did have to include enough clear and accurate information that someone reading the essay would understand most of the important points we covered.

Most essays received partial credit as a result of including incomplete or inaccurate information.

To determine your total points for this exam, add up the three scores for the three questions. The maximal number of points for this exam is thus a total of 30.   (Check the distribution of grades for this exam.)

To receive a straight B for the semester, you should earn a total of 90 points (an average of 18 points on each of 5 exams).   To receive a straight C, you should earn a total of 60 points (an average of 12 points on each of 5 exams).   At the end of the semester I also examine everybody's scores and award some extra credit for consistent improvement on exams (especially after the first exam).   The target for a B is subject to adjustment by me at the end of the semester.   The target for a C is engraved in stone!

If you would like me to regrade your exam, return your exam (all three questions) to me with a separate note about what you feel needs correcting before the next exam.

Most important ... I will be glad to talk to each of you about any exam. Good times are immediately after class or later in the afternoon (see me after lecture to arrange a time).


1. (10 minutes) Do moths recognize their own species?

Most essays described, sometimes in detail, the females' pheromones and the responses of males.   Many described how the size of pheromone molecules increases their specificity (differences among related species) but also increases their metabolic cost.   A crucial experiment was the study of four species of saturniid moths in the same habitat.   About 40% of males responded to their own species' pheromones but 20% responded to other species' pheromones, a result indicating that male moths made many mistakes.   Because there are few hybrids in nature, moths must have other ways to identify the correct females (for instance, signaling at different times of night or season, use of short-range signals, relying on compatible genitalia).   Many essays concluded that the pheromones are therefore just accurate enough to get the job done (finding a conspecific mate) -- and no more.

2. (10 minutes) Do birds recognize their young?

All essays agreed that birds do recognize their young, but not until they need to.   Many mentioned the comparison between gulls that nest of the ground on coastal islands and those that nest on cliffs.   In both cases, parents recognize their young only when the young leave the nest (after one week for the ground-nesting herring gulls, after three weeks for the cliff-nesting kittiwakes).   Most essays described the experiment for recognition of young, simply switching young of similar ages between nests.   Many essays also compared solitary and colonial swallows.   Some even included good accounts of the experiments with loudspeakers to demonstrate that in colonial swallows parents could recognize their own young by voice alone.   Furthermore, the young of colonial swallows have complex calls, which provide greater specificity (differences between individuals).   Once again, as many essays noted, recognition and specificity evolve only when needed.

3. (10 minutes) Do animals' calls have referents?

Many essays had a difficult time defining a referent (an external situation associated with a signal, not the signal itself).   Nearly all essays described food calls of house sparrows or alarm calls of birds, ground squirrels, or vervet monkeys.   Some also described the dances of honeybees.   But no essay had time to describe all of these examples fully.   The vervet monkeys, house sparrows, and honeybees, in particular, provided lots of relevant information.   Whichever examples were chosen, strong essays emphasized the association of different signals with different external situations and responses -- plus evidence that receivers responded appropriately to the signals alone and did not just imitate the signaler's response to the referent or respond to the referent itself.