Feeding patterns of rats when food-access cost is alternately low and high

Rats living in a laboratory foraging paradigm began each meal by bar pressing to procure access to food and then could eat any amount. In different conditions the procurement price changed from low (10 bar presses) to high (200 or 400 bar presses) every ten days, five days, or one day, or on schedules of one-day-low/two-days-high, or one-day-low/four-days-high. In a final condition, the price alternated at every meal. Meals were less frequent and larger on high-price days. In the ten- and five-day alternations, the rats adjusted meal frequency on the first day of a price, but changed meal size gradually over the first few days; by the fifth day, daily intake was not different on low- and high-price days. In the one-day alternations, the rats ate less food, and in some cases did not eat at all, on high-price days, and lost weight. Intake was greater than normal, and body weight recovered, on low-price days. This pattern saved foraging cost at the expense of greater-than-normal daily fluctuations in food intake and body weight. When two or four days of high price alternated with one day of low price, the rats did eat on the first day of high price, suggesting they may integrate costs over a time window greater than 24 h.