Quantitative evaluation of individual food intake by insectivorous vespertilionid bats (Chiroptera, Vespertilionidae)

Abstract

Insectivorous bats provide important ecosystem services, especially by suppressing and controlling the insects' biomass. To empirically quantify the number of insects consumed by European vespertilionid bats per night, we estimated their ratio of dry mass of feces to mass of consumed insects. This study combines the results of feeding in captivity and the data obtained in field surveys; dry mass of feces was measured in both cases. In captivity, we analyzed the effect of species, age and sex of bats, species of insects consumed and the mass of food portion on the dry mass of feces. Using coefficients of the regression model, we estimated the number of insects consumed by free-ranging bats based on dry mass of their feces. According to our estimates, on average, one individual of one of the largest European bat species, Nyctalusnoctula, consumes 2.2 g (ranging from 0.5 to 8.2 g) of insects per one feeding night, while the smallest European bats of genus Pipistrellus consume 0.4 g (ranging from 0.1 to 1.3 g), further confirming the importance of insectivorous bats for ecosystem services. This publication offers the novel method for the estimation of insects' biomass consumed by bats.

Keywords: Chiroptera; Ecosystem services; Insectivorous bats; Insects; Ukraine.

Fig. 1.

Visualization of linear models for the mass of feces of bats versus the mass of feed provided. Mass of feces of N. noctula and E. serotinus presented on charts A (fodder insects), B (wild insects) and C. Lines are trend lines, shaded areas are 95% confidence intervals, points represent individuals used in the experiment. Dry mass of P. kuhlii (D) feces after consumption of 1 g of feed containing one of the four insect species (lines are median, box: 25/75 percentile, dot: outlier). Stages of insect metamorphosis are marked as: L, larva and I, imago; the fodder insects belong to such orders Z. morio, T. molitor - Coleoptera, A. domesticus - Orthoptera, B. lateralis, Blattodea.

Fig. 2.

Violin plots for estimated amount of food consumed by free-ranging N.noctula (n=95) and Pipistrellus spp.* (P. nathusii, P. pygmaeus, P. kuhlii; n=33) during one feeding session. Black dots mark median values and grey-colored areas mark the distribution of estimated amounts of food. *The data for the mass of feces from the three Pipistrellus species were combined.