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Bats of Fort Collins and the Surrounding Areas

The bat fauna of Fort Collins is dominated by big brown bats, particularly adult females and young of the year. Adult male big brown bats occur at higher elevations in the adjacent mountains. A comparison of the bat fauna of Fort Collins and the adjacent mountains suggests that anthropogenic change in the form of urban/suburban development has favored big brown bats. They seem more prone to adapt to roosting in buildings than most other species of bats. It is likely that prior to human settlement and building, big brown bat females roosted in snags and rock crevices along the lower, hotter slopes (very warm roosts are advantageous for growth and development of the young) in summer whereas males remained at cooler elevations to take advantage of daily torpor. Once buildings were constructed, anthropogenic roosts with very warm attics and wall spaces became available in the adjacent prairies. The area also became subject to more permanent water in impoundments, and introduced vegetation and associated herbivorous insects proliferated with subsidized water and fertilizers. The bat community in adjacent areas of the Rocky Mountains has a slightly different species composition and different sex ratios than that in Fort Collins.

Family Vespertilionidae

  • Big brown bat (Eptesicus fuscus)
  • Hoary bat (Lasiurus cinereus)
  • Silver-haired bat (Lasionycteris noctivagans)
  • Red bat (Lasiurus borealis)
  • Little brown bat (Myotis lucifugus)
  • Long-legged myotis (Myotis volans)
  • Long-eared myotis (Myotis evotis)
  • Fringed myotis (Myotis thysanodes)
  • Western small-footed myotis (Myotis ciliolabrum)
  • Townsend's big-eared bat (Corynorhinus townsendii)

Big brown bat (Eptesicus fuscus)

Hoary bat (Lasiurus cinereus)

Silver-haired bat (Lasionycteris noctivagans)

Red bat (Lasiurus borealis)

Long-legged myotis (Myotis volans)

Long-eared myotis (Myotis evotis)

Western small-footed myotis (Myotis ciliolabrum)

Bat Fauna of Fort Collins

We captured 506 bats of 7 species in mist nets set on 73 nights at 19 locations in Fort Collins parks and Natural Areas (Fig. 1). The city bat fauna was dominated by big brown bats, particularly adult females (74 % of adults were female; Table 1). Little brown bats were second in abundance, also mostly adult females (89 % of adults; Table 1). Together these two species represented over 90 % of the bats captured. Pregnant or lactating female big brown bats and little brown bats were recorded, as were juveniles of both these species, documenting reproduction by these bats in the city. Other species of bats taken in mist nets in Fort Collins (in order of abundance, each < 5 % of the total) were hoary bats, silver-haired bats, western small-footed myotis, long-legged myotis, and one eastern red bat (Table 1). The two species of myotis other than the little brown bat were represented by 2 western small-footed myotis (both lactating females taken on 7 and 27 July 2005) and 2 long-legged myotis (both adult females, not pregnant or lactating). Most of the hoary bats and silver-haired bats were taken in migration. The eastern red bat was a single record on 30 July 2003 (documented in greater detail by Neubaum, 2005). [pdf]

Bat Fauna of Adjacent Mountains

In areas of the Rocky Mountains west of Fort Collins (Fig. 2) we captured 635 bats at 23 locations in 2003-2005. Species composition and reproduction in bats in the adjacent mountains differed from that of the bat community in the city, and appeared to vary by elevation zone. At lower elevations in the mountains (mean 12.5 +/- 6.4 km from the city limits) the bat community was somewhat similar to that found in the city. Big brown bats were the most abundant species, followed by little brown bats (together making up 72 % of the captures). However, big brown bats constituted a smaller percentage of the total captures than in the city (39 % vs. 68%) and the proportion of males among adults was also higher (43 % vs. 26% in the city). Little brown bats were a slightly larger proportion of the total captures at mountainous locations < 2000 m elevation than in the city, but the proportion of adults that were male increased from 11.0 % in the city to 40 % . Low numbers of hoary bats and silver-haired bats were taken at both city and mountain sites. In addition, the species composition and relative abundances of the bat community at the lower elevation mountain sites included two species of myotis not taken in mist nets in Fort Collins (M. evotis and M. thysanodes), a greater number of long-legged myotis, and no red bats.

Above elevations of 2000 m (mean 21.3 +/- 9.0 km from Fort Collins) we captured 9 species of bats (6 in common with the city bat community). Long-legged myotis constituted the majority of bats captured at the upper elevations, and captures of this species included juveniles and pregnant and lactating females . Big brown bats and little brown bats combined accounted for just 19.2 % of the total captures above 2000 m . Although juveniles and reproductive adult female little brown and big brown bats were taken at these sites, the preponderance of captures of these two species at sites > 2000 m were adult males (78 %), the opposite of our findings in the city. Adult males of four other species also were captured in greater proportions than adult females above 2000 m: silver-haired bats, hoary bats, long-eared myotis, and possibly fringed myotis.

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