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Not well documented. Soft peeps from newly hatched young, up to 1–2 wk of age; appear to be food-begging (solicitation) calls—given when female presents food or when distressed (cold) and in need of brooding. Also a soft version of Guard Call (see below) at this age (Bretagnolle and Thibault 1993). Stronger, louder, more insistent begging develops by 2–3 wk of age; Alarm Calls (see below) by 4–5 wk. Young near fledging age give Alarm Calls in response to human near the nest (AFP).
From Bretagnolle and Thibault 1993, who distinguished 5 types of calls: Alarm; Solicitation (food-begging); Guard; Excited; Screaming. Female’s calls generally stronger and lower-pitched than those of male, perhaps owing to larger body size (see Poole 1989a: Fig. 6.19).
Guard Call, given by both sexes, a series of slow, whistled notes, falling rapidly in pitch (3.8 to about 2 kHz); Y. Prevost (in Cramp and Simmons 1980b) suggested these sound like a whistling kettle taken rapidly off a stove (tiooop, tioooop, tiooop). Given when an intruding Osprey begins to approach caller’s nest or perch, usually at some distance away (0.1–0.3 km). Most frequent behaviors (6% of 88 observations by [Bretagnolle and Thibault 1993] in Corsica) that accompany this call: alighting, flight, and (nest) defense. Guard Call may grade into Excited and Screaming calls as intensity of threat increases (see Behavior: Agonistic Behavior). In latter 2 calls, pitch wavers; sounds more intense—almost a squeal.
Screaming Call is same call used by male in Sky-Dance sexual display (see Behavior: Sexual Behavior). Male flies undulating, U-shaped pattern over nest area, often carrying a fish, calling. A distinctive sound at Osprey nesting colonies, especially as breeding season begins.
Alarm Call, given by female more than male in Corsica, given when a potential predator (non-Osprey) or disturbance (boat, human, vehicle) approaches nest. Generally given at nest or a perch; also in flight. Not always given by breeders; perched Ospreys in migration will Alarm Call (AFP). Composed of short, clear whistles that fall in pitch (4–2 kHz; see Fig. 4 in Bretagnolle and Thibault 1993). The only call that conveys a signal exclusive of visual displays; alarm display generally occurs before the call itself. Distance from nest at which Alarm Call is given depends on stimulus and individual’s habituation, but generally given only within 50–100 m of nest or perch. This call often changes to a harsh, guttural croak when birds are stressed by humans very close to their nests (perhaps the “excited call” of Bretagnolle and Thibault 1993).
Solicitation Call, given only by female, has 3 gradations (low to high) distinguished by (Bretagnolle and Thibault 1993). This is a food-begging call, heard often throughout season in Osprey breeding colonies. Presence of male near nest significantly elicits this call. Highest gradation heard when male has fish. Unclear to what extent males respond to this begging call; some males relinquish fish soon after hearing it, others ignore call for hours (AFP). Females also beg when mates are perched nearby without a fish; may be a stimulus for males to leave on fishing forays.
Bretagnolle and Thibault 1993 believed that calls (apart from Alarm Call) do not act as signals by themselves, but indicate degree of motivation of emitter. Evidence as follows: (1) Calls nearly always accompanied visual displays; rarely uttered alone. (2) Calls not associated with any specific display (see Behavior: agonistic behavior, below). (3) No significant difference between male and female calls when an intruder flies over nest, whereas sex-biased responses occur with visual displays.
All calls generally associated with breeding, except Guard and Alarm, which may be given by nonbreeders away from nest (e.g., individuals in migration). Sexual differences discussed above.
None. Given in response to immediate stimulus (see above).
None with a communicative function.