Foraging Ranges of Insectivorous Bats Shift Relative to Changes in Mosquito Abundance

Abstract

The need to develop effective management strategies for insectivorous bat populations requires an understanding of factors influencing habitat use. Availability of pest prey, such as mosquitoes is likely to be one such factor. To assess whether this is the case, we radio-tracked Vespadelus vulturnus Thomas (little forest bat), a predator of Aedes vigilax Skuse (saltmarsh mosquito), in saltmarsh and adjacent coastal swamp forest during periods of high and low Ae. vigilax abundance. When mosquito abundance in structurally-open saltmarsh was similar to the more cluttered coastal swamp forest, use of saltmarsh by V. vulturnus was disproportionately greater than its availability, with saltmarsh selected preferentially for foraging. However, at times of low Ae. vigilax abundance in saltmarsh, use of saltmarsh by V. vulturnus was reduced and all habitats were used in proportion to availability in the study area. This is the first radio-tracking study to demonstrate a shift in foraging range by an insectivorous bat species correlated with fluctuations in the distribution and abundance of a particular prey resource. The shift in foraging range by V. vulturnus, corresponding with a spatio-temporal variation in abundance of Ae. vigilax highlights the importance of mosquitoes as a dietary item. Broadscale pest control of Ae. vigilax may have ecological implications for the diet and habitat use of V. vulturnus. An adaptive management approach is proposed, whereby careful monitoring of insectivorous bat populations is recommended before and after any application of broadscale mosquito control measures. We also suggest a precautionary approach is taken such that broadscale control of mosquitoes avoids the lactation period of bats, a time when their energetic demands are greatest and when there is reduced risk of contracting mosquito-borne diseases transmitted by Ae. vigilax.

Does Thinning Homogenous and Dense Regrowth Benefit Bats? Radio-Tracking, Ultrasonic Detection and Trapping

“…The main threatening processes for N. corbeni are considered to be extensive loss of habitat through clearing for agriculture, grazing and altered fire regimes [39], with different forestry activities having contrasting effects [28]. The fourth study species, V. vulturnus, is the smallest bat in the study area (Table S1) and was selected because individuals were expected to forage within a 1-km radius [40][41][42], thus making the species highly suited, at a local scale, for revealing relative use of thinned and unthinned forest. It is a common species belonging to the edge-space ensemble based on its classic frequency modulated-constant frequency (FM-CF) echolocation call structure, but with relatively slow and manoeuvrable flight due to low wing aspect ratio and loading [43,44].…”

Importance of Riparian Zone: Effects of Resource Availability at Land-water Interface

“…Bats -Riparian zones provide numerous benefits for insectivorous bats, including favorable open habitats in the middle of a wooded area, water availability, and emergent aquatic insects as food resource [53,57,[64][65][66][67][68][69]. Yoshikura et al (2011) found that species richness and total abundance of two tree-roosting specialists (Myotis ikonnikovi, Murina ussuriensis) and the Japanese largefooted bat (M. macrodactylus) were significantly higher in riparian habitats than those in non-riparian habitats [70].…”

Mosquito Consumption by Insectivorous Bats: Does Size Matter?

“…Additionally, V. vulturnus shifted foraging ranges relative to changes in the distribution and abundance of Ae . vigilax [18], suggesting that the mosquito may be an important prey item in the study area. However, given the small size of mosquitoes, they may not be available to all insectivorous bats.…”