Measuring Behavior 2005: Cameron and White

Remote measurement of milk intake for studies of maternal investment in mammals

E.Z. Cameron and A.M. White

Department of Natural Resources and Environmental Science, University of Nevada, Reno, NV, USA

Parental investment is usually measured as the resources allocated to the offspring, or parental input. In mammals, the most obvious parental inputs are the resources transferred during lactation which are more energetically costly than the prenatal costs of gestation. In studies of mammalian parental investment an estimate of milk obtained by offspring is therefore a fundamental measure of parental input and consequently behavioral measures of suckling have been used to estimate amounts of milk transferred. Such studies assume that, all other factors being equal, offspring that suckle more obtain more milk. However, it is unlikely that other factors are equal, and therefore there is doubt that time spent suckling indexes milk intake, and studies have questioned the reliability and utility of such estimates of milk intake. Despite the doubt surrounding behavioral measures of milk intake, and the potential for the use of isotope labeling for measuring milk transfer, field studies have not used alternatives to behavioral measures of milk intake. Isotope techniques use labeled water (typically tritium or deuterium) based on the principle that all body water should be equivalently labeled with radioisotopes. We are developing a remote technique involving darting the radioisotope into a mother and measuring transfer based on fecal samples instead of blood plasma samples. The technique will allow the remote measurement of milk transfer and therefore maternal input in a range of mammalian field studies. We report here on the development of the technique and its uses for measuring maternal investment in cooperatively breeding mammals.

Paper presented at Measuring Behavior 2005 , 5^th International Conference on Methods and Techniques in Behavioral Research, 30 August - 2 September 2005, Wageningen, The Netherlands.