Bats and insects over two Scottish rivers with contrasting nitrate status

Abstract

The abundance of foraging bats (Pipistrellus pipistrellus and Myotis daubentonii) and flying insects over two rivers in north-east Scotland (Dee and Ythan), differing eightfold in nitrate levels, were compared by paired samples over three periods in summer 1995, during each of which 10 nights' sampling was undertaken using ultrasonic detectors and insect suction traps. Thirteen out of the 18 pairwise comparisons of bat passes, insect numbers, biomass and diversity were not significantly different. The oligotrophic Dee supported higher numbers of bats than the eutrophic Ythan in June, but this was attributed to an effect of adverse weather conditions affecting the Ythan. In July and August-September, neither bat abundances nor the abundance of Chironomidae and Trichoptera, the main food of the bats, differed significantly between the two rivers, although the Ythan showed higher total insect biomass than the Dee. The Ythan also showed a much higher abundance of small Diptera, mainly Psychodidae and Cecidomyiidae, associated with elevated nitrogen levels in the intensively farmed river valley. Thus a small eutrophic river can support as many bats and as high an insect density as a large oligotrophic one.

Activity of Insectivorous Bats Associated with Cattle Ponds at La Michilía Biosphere Reserve, Durango, Mexico: Implications for Conservation

“…Some bat species (Pipistrellus pipistrellus, Eptesicus serotinus and Myotis sp.) respond to the presence of cattle, presumably because presence of dung increases the amount of available nutrients that promote the development of invertebrates on which bats feed (Shiel et al, 1991;Robinson and Stebbings, 1993;Racey et al, 1998). It is possible as well that the animals themselves disturb ground insects while they graze, facilitating predation by bats (Downs and Sanderson, 2010).…”

Carpe noctem: the importance of bats as bioindicators

“…In a study designed to test this hypothesis, Racey et al (1998) found little difference between the numbers of bats and insects foraging over a small eutrophic river and a large oligotrophic one. Park & Cristinacce (2006) investigated the effect on foraging bats of phasing out percolating filter beds, which provide breeding opportunities for dipterans, in favour of activated sludge, for treating human sewage.…”

Sex and Age Related Habitat Selection and Mass Dynamics of Daubenton's BatsMyotis daubentonii(Kuhl, 1817) Hibernating in Natural Conditions

“…860% (Kokurewicz, 1995). This population growth may reflect the increased availability of insect prey, notably midges (Diptera: Chironomidae), caused by eutrophication processes (Kokurewicz, 1995;Racey et al, 1998). In that context the decline in the maximal number of bats observed in the mine exceeding 19% is most probably the real effect of disturbance.…”