Abstract: Domestic hens were exposed to progressive-ratio 2 and progressive-ratio 10 schedules of food delivery with different initial ratios (2, 10, 20, 30, and 40). Breaking points, defined as the largest ratios completed before responding ceased for 600 consecutive seconds, were recorded under all conditions. In general, breaking points were higher under the PR 10 schedule than under the PR 2 schedule, and the value of the initial ratio did not systematically affect the breaking point. The former finding suggests that relative satiation affected breaking points in the present study, but the latter finding suggests that the primary determinant was the `price' of the reinforcer, defined in terms of the number of responses required to produce it. Breaking points were similar under conditions where initial ratios changed from session to session and under more conventional conditions, where initial ratios remained unchanged over several sessions.

Abstract: Abstract
In response to a request published in Equus, a magazine for those interested in horses, 85 owners of older geldings exhibiting sexual behavior completed history forms. The mean age of geldings was 16 f 5 years. Only 39 of the owners had had the gelding for at least a year before the behavior was noted. These cases could be used to determine the true age of onset of the problem. When log survivorship was used to determine whether there were one or two different populations, a break or change in the slope at age 16 indicated that there are two populations. One population shows the behavior from the time of castration and the other first exhibits the behavior in old age, possibly in response to an ACTH secreting pituitary adenoma. A total of 40% of the horses were Quarterhorses, the most numerous breed in the US; 78% of the horses were purebreds. Fewer than half the owners knew the age at which their horse had been castrated because they did not own the horse at the time.
The mean age at castration, when known, was 3.3 f 2.5 years. The reason for contacting us was sexual behavior (70%), aggression (24%). or some other problem ( 1 o/o). Whether or not aggression was the presenting problem, most of the horses showed aggression (95%), particularly towards other geldings (88%)) but also towards people (3 1%). Copulatory behavior (mounting) was shown by 69% of the geldings and half of those were able to intromit. These findings indicate that the sexual behavior of geldings is a problem for owners and that aggression usually accompanies sexual behavior.
The owners were encouraged to send serum samples taken before and after human chorionic gonadotropin (HCG) administration for testosterone and estrone sulfate analysis to determine whether residual testicular tissue was responsible for the horse’s behavior. Of the 14 horses tested, only one had elevated levels of testosterone indicating that there was residual testicular tissue. A total of six of the owners agreed to treat their horses with cyproheptadine at a dose of 8 mg day- ’ gradually increased to 88 mg day- ’ per horse. A total of three of the horses showed a decline in sexual and aggressive behavior, one got worse and two had side effects and treatment was withdrawn.

Abstract: Appleby (1983, Anim. Behav., 31, 600-608) described a statistical test, based on the work of Kendall (1962, Rank Correlation Methods), for the significance of linearity in dominance hierarchies. He suggested that unknown relationships should be assigned the value 1/2 and that subsequently the same test procedure can be used. In this paper it is shown that incorrect results are obtained by this method whenever there are unknown relationships. Values of the linearity index are systematically too low. P-values can be too high (underestimating the significance) or too low (overestimating), and seem to differ by not much more than a factor two (respectively a half) from the correct P-value. An improved method is developed for testing linearity in a set of dominance relationships containing unknown relationships. Furthermore, it is argued that, if one admits the possibility of tied dominance relationships, which should indeed be assigned the value 1/2, Landau's linearity index is to be preferred to Kendall's index. A randomization test is developed for assessing the significance of linearity or non-linearity in a set of dominance relationships containing unknown or tied relationships. The test statistic employed in this testing procedure is based on Landau's linearity index, but takes the unknown and tied relationships into account.