Full Description

"The mating sounds (boatwhistles) of nesting batrachoidid Halobatrachus didactylus males were recorded in the Tagus Estuary from piers."

"The acoustic features that consistently best discriminated individuals were the dominant frequency of the middle tonal segment of the boatwhistle (P2) and dominant frequency modulation, followed by P2 pulse period, amplitude modulation and sound duration. These results suggest the possibility of individual recognition based on acoustic cues."

"Since territorial males nest close together, boatwhistles are emitted in choruses resulting in a very conspicuous acoustic output (dos Santos et al., 2000). In the peak of the breeding season, a small aggregation of males vocalizing close to the hydrophone can reach an average of 30 boatwhistles min 1 (Amorim et al., 2006). The boatwhistle is a tonal multi-harmonic sound lasting c. 800 ms (Amorim et al., 2006). The fundamental frequency is c. 60 Hz [H1; Fig. 1(b)] and the dominant frequency is typically either the second or the fourth harmonic (Fig. 1) (Amorim et al., 2006)."

"The classification used by dos Santos et al. (2000) that considers three distinct phases in the boatwhistle [beginning (P1), middle (P2) and end (P3)] was adopted. These three phases differ in pulse period and dominant frequency (dos Santos et al., 2000), with the pulse period typically decreasing and the dominant frequency increasing from phases 1–3 (see Table I)."

"The mating sounds of the H. didactylus varied considerably in duration ranging from 317 to 1290 ms (n _ 207 sounds analysed from all males), with average values of 767 ms (Table I). The fundamental frequency (H1) and the harmonics (multiples of H1) showed a slight frequency modulation that was more obvious in the higher harmonics (Fig. 1). H1 was the dominant frequency in only one male that exhibited eight of the 16 sounds analysed with dominant frequencies in the H1 and the remaining in the H2 (see male 5 in Fig. 5). H4 was the most common dominant frequency (51 2%) followed by H2 (44 9%). The three segments (P1, P2 and P3) that make up the boatwhistle (dos Santos et al., 2000) were characterized by different durations, pulse periods, relative amplitude and dominant frequencies (Table I). The tonal phase of the boatwhistle (P2) was the longest segment, lasting on average 56% of the sound, and exhibited an intermediate pulse period and dominant frequency to P1 and P3. The boatwhistle dominant frequency typically corresponded to P2 dominant frequency. Pulses in P1 and P3 were of a more irregular shape and had clear starts and ends (Fig. 4), while pulses in P2, the tonal segment, were more regular and fused together sometimes resembling a sinusoidal wave (Fig. 4). The third boatwhistle segment was more variable in duration, pulse number, pulse period and dominant frequency than the two previous segments (Fig. 4 and Table I) and was not present in all males."

"Boatwhistles were distinct between individuals in terms of waveform (amplitude modulation) and spectral characteristics (Fig. 1). Detailed waveform patterns were also distinctive among calling males (Fig. 6)."

"All variables were significantly more variable between than within males and thus could all potentially provide cues to identify individuals."

"In the field, males can probably only detect a maximum of eight males at a time (maximum size of a chorus; unpubl. data) and call often in duets or in trios, thus potentially making the task of individual recognition simpler than the 13 males considered in the present study. Moreover, because males call often at rates of c. 10 boatwhistles min -1 (pers. obs.) they will easily experience more than the 16 calls from a neighbour having more opportunity to access distinct features from stationary nesting conspecifics."

"Boatwhistles are thought to function both to announce territorial ownership and position to other males and to attract females as prospective mates (Winn, 1967)."

Observation Environment Quotes

"The nest was naturally occupied by the male and its entrance was closed with a plastic mesh that allowed prey items to enter the nest but prevented the subject male from abandoning the nest during recordings."

Behaviour Description Quotes

"The mating sounds (boatwhistles) of nesting batrachoidid Halobatrachus didactylus males were recorded in the Tagus Estuary from piers."

"Nesting males use an advertisement call (the boatwhistle) to attract females that results from the contraction of sonic muscles attached to the swimbladder (dos Santos et al., 2000)."

"Boatwhistles are thought to function both to announce territorial ownership and position to other males and to attract females as prospective mates (Winn, 1967)."

Sound Name Quotes

"The mating sounds (boatwhistles) of nesting batrachoidid Halobatrachus didactylus males were recorded in the Tagus Estuary from piers."

"The acoustic features that consistently best discriminated individuals were the dominant frequency of the middle tonal segment of the boatwhistle (P2) and dominant frequency modulation, followed by P2 pulse period, amplitude modulation and sound duration. These results suggest the possibility of individual recognition based on acoustic cues."

"Since territorial males nest close together, boatwhistles are emitted in choruses resulting in a very conspicuous acoustic output (dos Santos et al., 2000). In the peak of the breeding season, a small aggregation of males vocalizing close to the hydrophone can reach an average of 30 boatwhistles min 1 (Amorim et al., 2006). The boatwhistle is a tonal multi-harmonic sound lasting c. 800 ms (Amorim et al., 2006). The fundamental frequency is c. 60 Hz [H1; Fig. 1(b)] and the dominant frequency is typically either the second or the fourth harmonic (Fig. 1) (Amorim et al., 2006)."