M. Bateson et A. Kacelnik, PREFERENCES FOR FIXED AND VARIABLE FOOD SOURCES - VARIABILITY IN AMOUNT AND DELAY, Journal of the experimental analysis of behavior, 63(3), 1995, pp. 313-329
Much research has focused on the effects of environmental variability
on foraging decisions. However, the general pattern of preference for
variability ill delay to reward and aversion to variability in amount
of reward remains unexplained at either a mechanistic or a functional
level. Starlings' preferences between a fixed and a variable option we
re studied in two treatments, A and D. The fixed option was the same i
n both treatments (20-s fixed-interval delay, five units food). In Tre
atment A the variable option gave two equiprobable amounts of food (20
-s delay, three or seven units) and in D it gave two equiprobable dela
ys to food (2.5-s or 60.5-s delays, five units). In both treatments th
e programmed ratio [amount/(intertrial interval + latency + delay)] in
the fixed option equaled the arithmetic mean of the two possible rati
os in the variable option (ITI = 40 s, latency = 1 s). The variable op
tion was strongly preferred in Treatment D and was weakly avoided in T
reatment A. These results are discussed in the light of two theoretica
l models, a form of constrained rate maximization and a version of sca
lar expectancy theory. The latter accommodates more of the data and is
based on independently verifiable assumptions, including Weber's law.