The aim of this study was to compare the demand by possums for foods under different arrangements of concurrent progressive-ratio and fixed-ratio schedules of reinforcement. In Experiment 1, every possible food pair made up of berries, chicken, egg, foliage, insects and mushroom was presented (30 pairs in total). The requirement on the progressive-ratio schedule increased within a session and the fixed-ratio was kept constant at 30. In Experiment 2, a subset of the foods from Experiment 1 were used (chicken, mushroom, egg and berries) and in separate conditions the fixed-ratio was either 30 or 10 responses. In Experiment 3, the foods were the same as used in Experiment 2 and the progressive-ratio schedule increased every five sessions and the fixed-ratio schedule was 30 responses. Exponential models of demand were applied to consumption rates to compare the parameters of initial demand, essential value and P _max , and break point and cross point across foods. The models described the data well and consumption rates were similar when the incrementing schedules increased within- and across sessions. Demand was highest for berries, egg and locust in Experiment 1 and egg and chicken in Experiments 2 and 3. This finding has practical implications for understanding possum food preferences in the wild as a function of other available food sources.

Guinea pigs (Cavia porcellus) are popular pets and used as laboratory animals, however, their dietary preferences are under-studied. It is important for guinea pig owners and carers to increase the opportunity for good animal welfare by providing personalized and enriching dietary options. Thus, this study aimed to assess the use of paired-stimulus and multiple-stimulus-without-replacement preference assessments to determine the food preferences of seven male guinea pigs and test the validity of the methods by testing the demand for the most- and least preferred foods as reinforcers for climbing an elevated ramp. Generally, the preference assessments identified the same foods as the most preferred for each guinea pig, but not the least preferred foods. Guinea pigs climbed up to the steepest angle for both most and least preferred foods, but a non-linear least squares regression and demand analysis indicated faster climbing and inelastic demand for most preferred foods compared to slower climbing and elastic demand for least preferred foods. Both preference assessment methods were valid in identifying a preferred food, however, the multiple-stimulus-without-replacement assessment was more efficient to conduct. High-preference foods such as parsley and dandelion are recommended as future training reinforcers for guinea pigs and as foods to consider using as enrichment in captive guinea pig systems to encourage good welfare.