Corn Crake (Crex crex) Science Article 3
We tested whether the temporal parameters of corncrake (Crex crex) call change seasonally and/or individually. We defined a new, compound variable called RHYTHM, which quantitatively describes how corncrake call is perceived. Temporal parameters of calls, including RHYTHM, were significantly associated with both the time within the breeding season and body size. The most striking variation of call production was related to between-call intervals, which define a range of calls from monotonous (low values of RHYTHM) to intermittent (high values of RHYTHM). We found very clear, seasonally repeatable patterns of corncrake call with respect to syllable length, interval duration, and RHYTHM. Intermittent rhythm was more frequent in the beginning of the season, and to some extent before the second breeding attempt. While males sometimes changed call rhythm within a season, in general males with larger body size produced more intermittent calls. Simultaneously, intermittent rhythm was associated with less continuous and slower calling, leading to presumably lower energy expenditures. Building on previous results, we suggest that call rhythm is a conventional signal of aggressive motivation, with receiver retaliation as a possible stabilizing cost
Osiejuk, T. S., Olech, B., Ratynska, K., Owsinski, A. & Gromadzka-Ostrowska, J. 2004, Ann. Zool. Fennici 41: 647-659.