Myotis riparius Handley, 1960

Simmons, Nancy B. & Voss, Robert S., 1998, The mammals of Paracou, French Guiana, a Neotropical lowland rainforest fauna. Part 1, Bats, Bulletin of the American Museum of Natural History 237, pp. 1-219 : 145-146

Myotis riparius Handley

Figures 57 , 58

VOUCHER MATERIAL: 6 females (AMNH *267224, *267524, *268591, *268592; MNHN *1995.946, *1995.947) and 6 males (AMNH *266366, *266376, *267523, *268589; MNHN *1995.948, *1995.949); see table 57 for measurements.

IDENTIFICATION: As noted above, identification of species of Neotropical Myotis requires reference to LaVal (1973). Descriptions and measurements of Myotis riparius can also be found in Handley (1960) and Brosset and Charles­Dominique (1990). No subspecies of M. riparius are currently recognized (Koopman, 1994).

Our specimens of Myotis riparius conform to the description provided by LaVal (1973). A sagittal crest is present in all individuals, although it is poorly developed in two specimens; P3 is less than one­fourth the height of P4 in all individuals with both teeth (P3 is missing in one individual); and P3 is shift­ ed to the inside of the toothrow in 64% of our specimens. Most of our specimens of M. riparius have woolly brown dorsal fur and slightly lighter ventral fur. However, some individuals have fur that is silkier in texture, and one specimen (clearly adult based on epiphyseal fusion) is gray­brown with slightly darker underparts. Measurements of our material resemble those reported by Brosset and Charles­Dominique (1990) for French Guianan M. riparius , although our larger series exhibits somewhat more size variation (table 57).

FIELD OBSERVATIONS: We made 12 vouchered captures of Myotis riparius at Paracou: 11 individuals were taken in ground­level mistnets and 1 was shot as it flew back and forth in a regular beat about 5 m above a narrow dirt road at night. Of the 11 groundlevel mistnet captures, 5 were in well­drained primary forest, 4 were in swampy primary forest, 1 was in creekside primary forest, and 1 was in a manmade clearing.

The observed habitat difference in groundlevel mistnet capture frequencies between Myotis nigricans and M. riparius is noteworthy despite the rather small numbers of vouchered captures available for comparison (table 58). Apparently, M. nigricans favors clearings whereas M. riparius is more commonly found beneath the primary forest canopy. To our knowledge, ecological differences between sympatric populations of these species have not previously been reported in the literature, possibly due to the difficulty of field identification.

In addition to the vouchered captures of Myotis nigricans and M. riparius reported above, we recorded five unvouchered captures of Myotis in ground­level mistnets over roadside puddles. These bats were identified in the field as representing either M. nigricans or M. riparius , but were released without adequate confirmation of identification.

Figures

Fig. 57. Dorsal (A) and ventral (B) views of the skull of Myotis nigricans (AMNH 267228; female) from Paracou. Dorsal (C) and ventral (D) views of the skull of M. riparius (AMNH 268591; female) from Paracou. Note differences in structure of the anterior braincase, palate, and auditory region. Scale bars = 5 mm.

Fig. 58. Lateral views of the skull and lower jaw of (A) Myotis nigricans (AMNH 267228; female) and (B) M. riparius (AMNH 268591; female). Scale bars = 5 mm.