Estimates of Food Consumption by the Lizard Lacerta vivipara Jacquin

Summer-autumn feeding ecology of Pied Flycatchers Ficedula hypolueca and Spotted Flycatchers Muscicapa striata: the importance of frugivory in a stopover area in north-west Iberia

“…Currently, the 'energy assimilation hypothesis' best explains fruit consumption by migrating passerines, with an energetic advantage and more rapid increase in body mass thanks to omnivory rather than strict insectivory, though a large quantity of fruits needs to be consumed (Parrish 1997, Eggers 2000, Berthold 2001, Bairlein 2003, Newton 2008. Some fruit species frequently consumed by migrating flycatchers in Iberia, such as Dogwood in the present study, have a high energy content, only slightly lower than that of insects (c. 5 kcal g À1 dry pulp for Dogwood as previously indicated, in comparison with 5.2-6.8 kcal g À1 dry weight for insects, according to Golley 1961, Avery 1971, Jordano 1981. Fruits are obtained more easily than insects because they are an immobile and predictable food source, concentrated in space and conspicuous.…”

Validation and use of 22Na turnover to measure food intake in free-ranging lizards

“…He derived equations which predict food intakes for an animal the weight of L. guichenoti (mean 1.01 g, Table 2) which are between 31% and 153% higher than the values found under equivalent physical conditions using 22 Na turnover. These deviations may be an artifact of the differences in techniques used to measure food intake (the faecal output/nitrogeneous wastes methods are reported to give high values (Avery 1971(Avery , 1978), or they may reflect differences in factors such as the activity of the animals, the availability of food, or differences in digestive physiology. Turner et al (1976) have suggested, on the basis of results from other authors, that the daily food consumption of lizards is probably about 5% of their body weight, except that smaller lizards may have higher consumptions than larger ones, because assimilated energy and body weight are related by a power function with an exponent of less than one (see below).…”

“…For example, Avery (1971Avery ( , 1978 used analysis of faecal output and/or nitrogenous wastes to measure food intake in three other small diurnal insectivorous lizards: Lacerta vivipara (1-5 g) in England, and Podarcis muralis and P. sicula (2-10 g) in Italy. He derived equations which predict food intakes for an animal the weight of L. guichenoti (mean 1.01 g, Table 2) which are between 31% and 153% higher than the values found under equivalent physical conditions using 22 Na turnover.…”

“…Direct estimates of food intake for free-living reptiles have been made previously by establishing a laboratory relationship between food intake and output of faecal or nitrogenous wastes, and then measuring the output of field-captured animals (Avery 1971(Avery , 1978(Avery , 1981Andrews and Asato 1977); or from a knowledge of the dietary water input and the water content of the food (Minnich and Shoemaker 1970;Nagy 1975;Nagy and Shoemaker 1975;Congdon et al 1982). However, the first of these methods is undesirable because the animals must be removed from the field for several days at each sampling; and the latter method is possible only for non-drinking animals.…”

“…These include: analysing the composition and rate of production of the faeces (Harris 1964); analysing gut contents and making assumptions about stomach capacity and its rate of fill (Johnson 1966;Congdon et al 1982); combining laboratory feeding regimes with estimates of field behaviour (Mueller 1970;Dutton et al 1975); and combining data on field energy expenditure with estimates of assimilation efficiency and secondary production (see Avery 1971Avery , 1978Avery , 1981Nagy 1975;Turner et al 1976;Bennett and Gorman 1979).…”