Nonbreeding Eastern Curlews Numenius madagascariensis Do Not Increase the Rate of Intake or Digestive Efficiency before Long-Distance Migration because of an Apparent Digestive Constraint

The possibility of premigratory modulation in gastric digestive performance was investigated in a long-distance migrant, the eastern curlew (Numenius madagascariensis), in eastern Australia. The rate of intake in the curlews was limited by the rate of digestion but not by food availability. It was hypothesized that before migration, eastern curlews would meet the increased energy demand by increasing energy consumption. It was predicted that (1) an increase in the rate of intake and the corresponding rate of gastric throughput would occur or (2) the gastric digestive efficiency would increase between the mid-nonbreeding and premigratory periods. Neither crude intake rate (the rate of intake calculated including inactive pauses; 0.22 g DM [grams dry mass] or 3.09 kJ min(-1)) nor the rate of gastric throughput (0.15 g DM or 2.85 kJ min(-1)) changed over time. Gastric digestive efficiency did not improve between the periods (91%) nor did the estimated overall energy assimilation efficiency (63% and 58%, respectively). It was concluded that the crustacean-dominated diet of the birds is processed at its highest rate and efficiency throughout a season. It appears that without a qualitative shift in diet, no increase in intake rate is possible. Accepting these findings at their face value poses the question of how and over what time period the eastern curlews store the nutrients necessary for the ensuing long, northward nonstop flight.

Initiation of evasive manoeuvres during self-motion: a test of three hypotheses

To understand performance of evasive and interceptive actions it is important to know how people decide when to initiate a movement - initiating at the 'right' moment is often essential for successful performance. It has been proposed that initiation is triggered when a perceptually derived quantity reaches an invariant criterion value. Candidate quantities include time-to-collision (TTC), distance, and rate of image expansion ( ROE), all of which have received empirical support. We studied initiation of an evasive manoeuvre in a computer-simulated steering task in which the observer was required to steer through a stationary visual environment and avoid colliding with an obstacle in their path. The results could not be explained by hypotheses which propose that evasive manoeuvre initiation is based on a fixed criterion value of TTC or distance. The overall pattern was, however, consistent with the use of a criterion ROE value. This was further tested by analyses designed to directly evaluate whether the ROE value used to initiate the response was the same across experimental conditions. Only two of the six participants showed evidence for using the ROE strategy.

Factors affecting the vigilance and flight behaviour of impalas

This study investigated the influences of various natural and anthropogenic factors on the vigilance and flight behaviour of impalas in the Save Valley Conservancy, Zimbabwe, using multivariate statistical techniques. The factor that most significantly affected the proportions of time that individuals spent being vigilant and their rates of vigilance was the position of a focal animal in the group; impalas on the periphery of a group were more vigilant than central impalas. Both measures of vigilance were also negatively related to group size. Males spent more total time being vigilant but females raised their heads more often. Impalas spent more time being vigilant in the late afternoon than in the early morning, when greater than ten metres from cover, and when predators had been nearby within the previous six hours. Impalas spent more time vigilant at the property where more impalas were hunted, possibly reflecting the differences in the intensity of hunting by humans on the two properties. Flight distances at the approach of humans were significantly greater at one property than the other, and were also greater for small groups. Further research into the effects of hunting by humans on animals' antipredator behaviours would provide valuable insights for wildlife managers.