Ronald Orenstein <email@example.com
> This may well be true. I was struck, on the one occasion many years ago when I had to take wing measurements from bats on
> an OTS course in Costa Rica, how long and narrow the wings of molossids were compared to others. They seemed unable to
> take off even if we tossed them into the air on release. We had to release them on tree trunks, after which they climbed pretty
> much out of sight before taking off. The closest avian analogy in general wing shape that I could come up with was a shearwater
> or an albatross - which of course doesn't mean that molossids fly like albatrosses! They are probably too small, among other
> things. I presume they hunt above the canopy where manouverability isn't a big problem, but I admit I don't know.
Turns out you're spot on:
Voigt CC, Holderied MW (2012). High manoeuvring costs force
narrow-winged molossid bats to forage in open space. J. Comp.
Physiol. B. 182: 415-424. doi: 10.1007/s00360-011-0627-6.
Abstract: "Molossid bats are specialised aerial-hawkers that, like
their diurnal ecological counterparts, swallows and swifts, hunt for
insects in open spaces. The long and narrow wings of molossids are
considered energetically adapted to fast flight between resource
patches, but less suited for manoeuvring in more confined spaces, such
as between tree-tops or in forest gaps. To understand whether a
potential increase in metabolic costs of manoeuvring excludes
molossids from foraging in more confined spaces, we measured energy
costs and speed of manoeuvring flight in two tropical molossids, 18 g
_Molossus currentium_ and 23 g _Molossus sinaloae_, when flying in a
~500 m(3) hexagonal enclosure (~120 m(2) area), which is of similar
dimensions as typical forest gaps. Flight metabolism averaged 10.21 ±
3.00 and 11.32 ± 3.54 ml CO(2) min(-1), and flight speeds 5.65 ± 0.47
and 6.27 ± 0.68 m s(-1) for _M. currentium_ and _M. sinaloae_
respectively. Metabolic rate during flight was higher for the _M.
currentium_ than for the similar-sized, but broader-winged frugivore
_Carollia sowelli_, corroborating that broad-winged bats are better
adapted to flying in confined spaces. These higher metabolic costs of
manoeuvring flight may be caused by having to fly slower than the
optimal foraging speed, and by the additional metabolic costs for
centripetal acceleration in curves. This may preclude molossids from
foraging efficiently between canopy trees or in forest gaps. The
surprisingly brief burst of foraging activity at dusk of many
molossids might be related to the cooling of the air column after
sunset, which drives airborne insects to lower strata. Accordingly,
foraging activity of molossids may quickly turn unprofitable when the
abundance of insects decreases above the canopy."