429
15.4 Discussion
During 5 years we found humpback whale groups containing singer males in all the
extension of our study area, being about 520 km of coast. This confirm the large
distribution of the humpbacks in the Northeastern region of Brazil, going farther than
the core area of Abrolhos Bank, as previously commented (Rossi-Santos et al. 2008;
Wedekin et al. 2010).
The lack of sightings in the stretch of coast between north of Praia do Forte to
south of Aracaju may be probably due to the sampling route, always passing there
during the night, because navigating conditions in those cruises, which depart from
Praia do Forte to reach Aracaju during the early morning of the next day. However,
the sightings north and southwards of this place attest the presence of the humpbacks, and because its high mobility one may assume they do occur along all that
part of coast.
Despite the singer animals being typically described as alone males (eg. Payne
and McVay 1971; Clapham 1996; Darling and Berube 2001), singing behavior may
occur in other group composition, as the occasional escort males (eg. Baker and
Herman 1984; Frankel et al. 1995; Darling and Berube 2001), whose may sing
while escorting females with or without calves. Darling and Berube (2001) also
reported about 14 occasions where another male approached singer males.
In the present work, singer males were mostly found as alone individuals.
However singer males also occurred in groups varying from two to four individuals,
besides males accompanying females and calves. In one occasion, two singers in the
same group were confirmed by acoustic recordings. This show a large behavioral
flexibility from humpback whales in increase the chances to find a mate partner during the breeding season.
During many occasions we noted singer males typically smaller (referenced to the
boat as 8–9 m long animals), suggesting that young animals are using the study area
as a way to search for new territories even less competitive than the core area of
Abrolhos Bank, where traditionally large and old singer males utilize during the
breeding season. We suggest the employ of the photogrammetry method (eg. Spitz
et al. 2002) to access this hypothesis in next studies concerning body size estimation.
Humpback whale distribution in the study area may be related to ecological features such as oceanographic parameters of depth, continental shelf extension, while
tide and moon seems do not influence singer male distribution.
Meanwhile, behavioral factors such as female distribution are theorized in the
literature and may be determinant in the singer male occurrence during the breeding
season. As humpback whale apparently do not feed in the breeding areas, females
tend to move intensely, avoiding to meet with other female while, simultaneously,
looking for increase their mate chances. Post-partum ovulation, common in this
species, also benefits this high mobile female behavior and these factors together
result in an irregular female distribution (Clapham 1996; Clapham and Mead 1999).
The fact of the study area be located in a continental region, different from the
most of the described breeding areas, such as the Hawaiian Archipelago, (Au et al.
15 The Spreading Message in a Noisy World: Song Behavior and Acoustic Ecology…
15.4 Discussion
During 5 years we found humpback whale groups containing singer males in all the
extension of our study area, being about 520 km of coast. This confirm the large
distribution of the humpbacks in the Northeastern region of Brazil, going farther than
the core area of Abrolhos Bank, as previously commented (Rossi-Santos et al. 2008;
Wedekin et al. 2010).
The lack of sightings in the stretch of coast between north of Praia do Forte to
south of Aracaju may be probably due to the sampling route, always passing there
during the night, because navigating conditions in those cruises, which depart from
Praia do Forte to reach Aracaju during the early morning of the next day. However,
the sightings north and southwards of this place attest the presence of the humpbacks, and because its high mobility one may assume they do occur along all that
part of coast.
Despite the singer animals being typically described as alone males (eg. Payne
and McVay 1971; Clapham 1996; Darling and Berube 2001), singing behavior may
occur in other group composition, as the occasional escort males (eg. Baker and
Herman 1984; Frankel et al. 1995; Darling and Berube 2001), whose may sing
while escorting females with or without calves. Darling and Berube (2001) also
reported about 14 occasions where another male approached singer males.
In the present work, singer males were mostly found as alone individuals.
However singer males also occurred in groups varying from two to four individuals,
besides males accompanying females and calves. In one occasion, two singers in the
same group were confirmed by acoustic recordings. This show a large behavioral
flexibility from humpback whales in increase the chances to find a mate partner during the breeding season.
During many occasions we noted singer males typically smaller (referenced to the
boat as 8–9 m long animals), suggesting that young animals are using the study area
as a way to search for new territories even less competitive than the core area of
Abrolhos Bank, where traditionally large and old singer males utilize during the
breeding season. We suggest the employ of the photogrammetry method (eg. Spitz
et al. 2002) to access this hypothesis in next studies concerning body size estimation.
Humpback whale distribution in the study area may be related to ecological features such as oceanographic parameters of depth, continental shelf extension, while
tide and moon seems do not influence singer male distribution.
Meanwhile, behavioral factors such as female distribution are theorized in the
literature and may be determinant in the singer male occurrence during the breeding
season. As humpback whale apparently do not feed in the breeding areas, females
tend to move intensely, avoiding to meet with other female while, simultaneously,
looking for increase their mate chances. Post-partum ovulation, common in this
species, also benefits this high mobile female behavior and these factors together
result in an irregular female distribution (Clapham 1996; Clapham and Mead 1999).
The fact of the study area be located in a continental region, different from the
most of the described breeding areas, such as the Hawaiian Archipelago, (Au et al.
15 The Spreading Message in a Noisy World: Song Behavior and Acoustic Ecology…