Female pond bats hunt in other areas than males and consume lighter prey when pregnant

Abstract

Animals with large energy requirements are forced to optimize their hunting strategy, which may result in differentiation of the diet between sexes and across seasons. Here, we examined spatiotemporal variation in the diet of both sexes of the Pond Bat Myotis dasycneme, a species known to have spatial segregation of sexes when the young are born and lactating. Fecal pellets were collected from live animals for a period of 15 years at various locations in the Netherlands. A total of 535 pellets were successfully analyzed by microscopy and an additional 160 pellets by DNA metabarcoding. Morphological and molecular analyses showed that the diet of pregnant and lactating pond bats differed significantly from the diet of females with no reproductive investment. Further analyses of the data showed that pregnant female pond bats are highly dependent on small prey and pupae, mainly nonbiting midges and mosquitoes (Diptera: Chironomidae and Culicidae). These insects can be found in large quantities in peatlands intersected with shallow waterways, the habitat type in which female pond bats were observed more often than males. Our results suggest that during pregnancy the spatial segregation of sexes coincides with sex-specific diets, which might reflect habitat selection based on energy requirements, in addition to lowered intraspecific competition.

Keywords: Chiroptera; Myotis dasycneme; environmental DNA (eDNA); high-throughput sequencing; intraspecific competition; metabarcoding.

Fig. 1.

The summer distribution of the Pond Bat (Myotis dasycneme) population in the Netherlands (52°7ʹ57.5″N, 5°17ʹ28.6″E). The 114 locations where pond bats were captured (during the period 2003–2017) above waterways are indicated with filled circles. On the locations indicated with red (dark grey) circles, predominantly (>60%) females were caught; on the locations indicated with blue (grey) circles, predominantly (>60%) males were caught. The 106 open circles represent locations where mist nets were operated but no pond bats were caught. These locations are interpreted as being predominantly male or female based on nearby roost characteristics, but not used in analyses. Roosts used during the May–September months are indicated by light blue (male) and pink (female) diamonds, based on historic data (since 1900) and personal observations by the first author.

Fig. 2.

Proportion of pellets with at least one prey item detected for female (left) and male animals (right), separately per taxon. Top row: based on microscopy. Bottom row: based on DNA metabarcoding. Underlying data can be found in Haarsma et al. (2022).

Fig. 3.

Evenness (A) in prey over the nine taxonomic groups, Shannon diversity index (B), the proportion of all prey that are Chironomidae pupae (C), and average prey weight in mg per pellet, and separate per Pond Bat sex (left bars refer to females, right bars to males) and time period (I = end of hibernation till May 20, II = May 21 to June 29, III = June 30 to July 30, IV = July 31 until hibernation). Bars indicate standard errors. Different letters (a, b, c) indicate significant differences between bars. Significant differences between the first two and the latter two periods (and between periods I and II, and between III and IV) are indicated on top (see details in Supplementary Data SD3).

Fig. 4.

Pellet characteristics of female pond bats in periods I and II. Evenness (A) in prey over the nine taxonomic groups, Shannon diversity index (B), the proportion of all prey that are Chironomidae pupae (C), and average prey weight in mg (D) per pellet—and separated for pregnant females, lactating females, and females that were not currently investing in reproduction (i.e., post-lactating as well as immature females). Bars indicate standard errors. Different letters (a vs. b) indicate significant differences between bars. For analyses including other explanatory variables, see Supplementary Data SD4.