FLEXIBLE BAT ECHOLOCATION - THE INFLUENCE OF INDIVIDUAL, HABITAT AND CONSPECIFICS ON SONAR SIGNAL-DESIGN

Acoustic signals which are used in animal communication must carry a v ariety of information and are therefore highly flexible. Echolocation has probably evolved from acoustic communication, still serves such fu nctions and could prove as flexible. Measurable variability can indica te flexibility in a behaviour. To quantify variability in bat sonar an d relate it to behavioural and environmental factors, I recorded echol ocation calls of Euderma maculatum, Eptesicus fuscus, Lasiurus boreali s and L. cinereus while the bats hunted in their natural habitat. I an alysed 3390 search phase calls emitted by 16 known and 16 unknown indi viduals foraging in different environmental and behavioural situations . All four species used mainly multiharmonic signals that showed consi derable intra- and inter-individual variability in the five signal var iables I analysed (call duration, call interval, highest and lowest fr equency and frequency with maximum energy) and also in the shape of th e sonagram. A nested multivariate analysis of variance identified the influences of individual, hunting site, close conspecifics and of each observation on the frequency with maximum energy in the calls, and on other variables measured. Individual bats differed in multiple compar isons, most often in the main call frequency and least often in call i nterval. In a discriminant function analysis with resubstitution, 56-7 6% of a species' calls were assigned to the correct individual. Distin ct individual call patterns were recorded in special situations in all species and the size of foraging areas in forested areas influenced t emporal and spectral call structure. Echolocation behaviour was influe nced by the presence of conspecifics. When bats were hunting together, call duration decreased and call interval increased in all species, b ut spectral effects were less pronounced. The role of morphometric dif ferences as the source of individually distinct vocalizations is discu ssed. I also examined signal adaptations to long range echolocation an d the influence of obstacle distance on echolocation call design. My r esults allow to discuss the problems of echo recognition and jamming a voidance in vespertilionid bats.