CHIRPS, CHORUSES AND NOISE

Chirps, Choruses, and Noisy Evenings

What do many frogs, insects and birds have in common? They use acoustical signals--sound--to attract mates. Generally the male sings mightily, sometimes all day or all night, in hopes of attracting an interested female. Males may sing to demonstrate their strength, compared to other males, or to attract females to a territory. If competition pushes males to perform to their maximum capability, then these songs become a form of honest signalling of male condition

Male crickets, such as Acheta domesticus, the common household cricket, call to attract females. Producing the monotonous chirps for long periods of time must be taxing to the male crickets, making persistent calling an honest signal of male energetic capabilities. Females can discriminate male condition based on the calls, and are preferentially attracted to certain males (Gray 1997). Other males listen in and are attracted as well, preferring the same, generally larger, males (Kiflawi and Gray 2000). Why might males be attracted to the songs of other males, particularly those males who females prefer? Hack (1998) found that occasional chirps--advertisement calls--were cheaper for the males than walking around searching for mates, but that trilling--continuous calling used in courtship--was twice as expensive as chirping. Many other insects, such as periodical cidadas (Magicicada) also engage in acoustical contests to attract females (Cooley and Marshall 2001).

(Click here for a recording of cricket chirps.)

You've probably heard insects or frogs participate in a "chorus", in which all the seem to sing synchronously. Why might they do this? Greenfield and his research group have led the way in developing an understanding of why animals chorus (Greenfield 1994, Minkley et al 1995, Snedden and Greenfield 1998, Snedden et al. 1998). Perhaps the simplest model comes from species in which females have a preference for the first male in a group to sing. This "leading" male receives the female's attention. This, of course, puts pressure on the other males to sing ahead of the "leader". Ultimately, the males sing in chorus, because each is trying to be first. The amount of time between songs is governed by the males' recovery time and by the female's response to repeated songs. If the lag between a pair of songs is too short, then the female regards the second song as a "following" song. Once enough time has elapsed, then the female is receptive to a "leading" song. These factors combine to push the males into synchronous singing.

If dozens, hundreds, or even thousands of males participate in a chorus, auditory confusion may result for females. Consequently, at least in some species females have evolved mechanisms for selectively listening to a nearby subsample of the males (Snedden et al. 1998). This allows a female to evaluate the signals of individual males and use the information in choosing and locating her mate.

Other animals which chorus include katydids (Tauber 2001), humpback whales (Au et al. 2000), and chimpanzees (Mitani and Gros-Louis 1998).

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Gray DA 1997 Female house crickets, Acheta domesticus, prefer the chirps of large males Anim. Behav. 54: 1553-1562.
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Kiflawi M, Gray DA 2000 Size-dependent response to conspecific mating calls by male crickets Proc. Roy. Soc. London (B) 267: 2157-2161.
Minckley R L, Greenfield M D, Tourtellot M K 1995 Chorus structure in tarbush grasshoppers - inhibition, selective phonoresponse and signal competition Anim Behav 50: 579-594
Mitani J C, Gros-Louis J 1998 Chorusing and call convergence in chimpanzees: Tests of three hypotheses Behaviour 135:1041-1064
Schwartz JJ, Buchanan BW, Gerhardt HC 2001 Female mate choice in the gray treefrog (Hyla versicolor) in three experimental environments Behav. Ecol. Sociobiol. 49: 443-455
Snedden WA, Greenfield MD 1998 Females prefer leading males: relative call timing and sexual selection in katydid choruses Anim Behav 56: 1091-1098
Snedden WA, Greenfield MD, Jang YW 1998 Mechanisms of selective attention in grasshopper choruses: who listens to whom? Behav Ecol Sociobiol 43: 59 66
Tauber E 2001 Bidirectional communication system in katydids: the effect on chorus structure Behavioral Ecology 12: 308-312