The acuity of echolocation in Collocalia hirundinacea was studied by observing the birds' performances in an obstacle course constructed 10 m inside the mine they used as a roost. Birds flying into the mine missed 10 mm diameter rods significantly more often than rods 4 or 1.5 mm in diameter (73 % vs. 67% or 55%, respectively), but avoided even the 1.5 mm diameter rods. Birds flying through the obstacle course on their way out of the mine apparently, on some occasions, used vision to detect the rods, for they generally hit fewer rods than birds flying in. The orientation clicks of C. hirundinacea and their performances in the obstacle course were very similar to previous reports for the closely related Collocalia vanikorensis. The benefits of echolocation for Collocalia and the coincident distribution of Collocalia and a depauperate molossid bat fauna are discussed. Occupation of a cave or mine by the swiftlets does not preclude use of the same site by bats. THE ABILITY TO ECHOLOCATE is known from two groups of birds, the caprimulgid Steatornis caripensis (Griffin 1954) and at least four species in the apodid genus Collocalia (Griffin and Suthers 1970). In all of these birds the highest energy components of the orientation vocalizations are of low frequency ( < 10 KHz) relative to the orientation cries of microchiropteran bats, and consequently the acuity of their echolocation would not be expected to be as good as that of the Microchiroptera. The genus Collocalia includes from 12 to 20 species, depending upon which classification one follows (Mayr 1937; Peters 1964; Thomson 1964), and of these, C. brevirostris (Novick 1959), C. maxima (Medway 1959), C. fuciphaga (C. salangana; Medway 1967), and C. vanikorensis (Griffin and Suthers 1970) echolocate, while C. esculenta does not. To date there appear to be no other published data on orientation sounds, or their lack, in the remaining species. This study was undertaken to determine if Collocalia hirundinacea, a species very similar and perhaps closely related to C. vanikorensis, produced orientation sounds, and if it was capable of echolocation.
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