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Gerbils (Meriones unguiculatus) were allowed to forage during four periods in an environment that contained three bowls; one with sand, the second with 30 sunflower seeds mixed with sand, and the third with just seeds (during period 1) or 250 seeds mixed with sand (during periods 2, 3 and 4). During periods 1 and 2 the animals ate approximately 24 seeds from the 30 bowl. The behavior of working for food while "free food" is present was not influenced by whether or not that food really was "free" or if it was just a question of the amount of work required. During all three stable treatments (1, 2, and 4) the animals began by eating for about 15 min from the 30 bowl and only later changed over to the richest bowl. The big difference in behavior occurred in treatment 3 when the location of the bowls was changed. The animals took significantly less seeds from the 30 bowl (11 seeds), and no pattern like that from 1, 2, and 4 could be found. It is probable that the change in behavior between period 2 and 3 was elicited by the change in certainty of food resources. As the world became more uncertain the animals reduced the explorative part of their behavior and incrased the exploitative part, i.e. they came closer to being short term maximizers. Treatment 4 was equal to treatment 2 and done to control for any learning effects. No such effects were found

Animal. --- Animals. --- Behavior. --- Boxes. --- Control. --- Environment. --- Food. --- Forage. --- Foraging preferences. --- Gerbil. --- Gerbils. --- Great tits. --- Learning. --- Meriones unguiculatus. --- Meriones-unguiculatus. --- Mongolian gerbil. --- Mongolian-gerbil. --- Optimal prey selection. --- Pattern. --- Periods. --- Resources. --- Risk-aversion. --- Theory. --- Time. --- Treatment. --- Unguiculatus. --- Work.

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Sex steroid concentrations in the plasma of 24-day pregnant Mongolian gerbils (Meriones unguiculatus) and their male and female fetuses were measured using radioimmunoassays. It was found that, on Day 24 of gestation: (a) androgen levels were higher in those male fetuses developing adjacent to no female fetuses than in those male fetuses developing between two female fetuses and (b) androgen levels were higher in those female fetuses developing between two male fetuses than in those female fetuses with no immediate, male neighbours. Further, plasma taken from 24-day pregnant dams that had exhibited vaginal opening at a relatively early age had significantly lower androgen levels and significantly higher estradiol levels than did plasma taken from 24-day pregnant dams that had exhibited relatively late vaginal opening. The data provide direct evidence of hormonal mediation of previously described differences both in the morphology and reproductive biology of male and female adult gerbils as a function both of their fetal intrauterine locations relative to members of the other sex and of the age at vaginal introitus of their respective dams

Adult female mice. --- Adult. --- Age. --- Androgen. --- Behavior. --- Biology. --- Contiguity. --- Estradiol. --- Female. --- Fetal sex steroids. --- Fetuses. --- Function. --- Gerbil. --- Gerbils. --- Gestation. --- Hormonal. --- Intrauterine position. --- Level. --- Life. --- Male. --- Maternal sex steroids. --- Meriones unguiculatus. --- Meriones-unguiculatus. --- Mongolian gerbil. --- Mongolian gerbils. --- Mongolian-gerbil. --- Morphology. --- Neonatal androgen. --- Plasma. --- Proximity. --- Radioimmunoassay. --- Rats. --- Sex ratio. --- Sex. --- Sexes. --- Sexual maturation. --- Steroid-hormones. --- Steroid. --- Time. --- Unguiculatus. --- Uterine position.