Singing Schedules and Sites for a Tropical Burrowing Cricket (Anurogryllus muticus)

Abstract

When and where crickets call during a night should have important consequences for their reproductive success, yet little is known of individual calling behavior under natural conditions. This is particularly true in the tropics, where high temperatures throughout the night increase the opportunities for complex adaptations. Collectively males of A. muticus at Fort Sherman, Panama, called throughout the night; however, individual males seldom called more than three hours. Some males called close to their burrows and retreated into them when approached; others called on the ground away from any burrow and usually moved 1-6 m at intervals during their calling period. Males remained faithful to type of calling site on consecutive nights, and burrow-calling males used approximately the same calling periods. Individualized specialization as to time of calling may result from calling being energy costly and receptive females flying during most of the night. IN MOST CRICKET species, males make calling songs, sexually ready conspecific females use the calling song to move to the male, and courtship and insemination ensue. That this scenario is oversimplified is attested by masses of theory and an increasing array of facts-see, for example, Alexander 1975, Otte 1977, Cade 1980, Lloyd 1981, Gwynne and Morris 1982. This paper deals with two simple but generally neglected aspects of cricket calling: when and where males sing. WHEN MALES SING.-There are surprisingly few data on the daily cycles of calling for crickets outdoors. R. D. Alexander (1956, partly repeated in Dumortier 1963) diagrammed daily calling patterns for 26 species in eastern United States, indicating that all called during most of the night and that 19 called during daylight as well-though to a lesser degree. Alexander's diagrams gave no details as to changes in numbers of callers as a function of the day-night cycle nor did Alexander indicate whether the same individuals call during all times that the species can be heard. Alexander and Meral (1967), monitoring calling in Gryllus veletis and G. pennsylvanicus in southern Michigan, found that when nights were warm, both species sang chiefly at night; when nights were cold, calling occurred only during daylight. They reported that when nights were warm some veletis males (individuals identified by location) called only at while others chirped intermittently during the day and less steadily during the night, implying some individual specialization as to time of calling. Nielsen and Dreisig (1970) studied populations of Gryllus brunneri and G. bimaculatus outdoors in Morocco and reported that both called some in the afternoon and mostly at night; nighttime calling was sometimes curtailed by cold. They monitored four males of brunneri and one of bimaculatus at their burrows or in outdoor cages and learned that two brunneri males and the bimaculatus male called only at night. Cade (1979a) reported hourly counts of calling males of a Texas Gryllus sp. during four nights. Calling occurred all and on the three nights that populations were high, he noted a threeto fourfold increase in numbers calling immediately before and during sunrise. Forrest (1980, 1981) and T. Walker (1980) are apparently the only investigators who have quantified the calling times of numerous individual males outdoors. In the three species they studied, Scapteriscus acletus, S. vicinus, and Azurogryllus arboreus, calling was limited to within two hours after sunset, and all males sang during the minutes of peak call-