Description: The Omura’s whale ( Balaenoptera omurai ) was described as a new species in 2003 and then soon after as an ancient lineage basal to a Bryde’s/sei whale clade. Currently known only from whaling and stranding specimens primarily from the western Pacific and eastern Indian Oceans, there exist no confirmed field observations or ecological/behavioural data. Here we present, to our knowledge, the first genetically confirmed documentation of living Omura’s whales including descriptions of basic ecology and behaviour from northwestern Madagascar. Species identification was confirmed through molecular phylogenetic analyses of biopsies collected from 18 adult animals. All individuals shared a single haplotype in a 402 bp sequence of mtDNA control region, suggesting low diversity and a potentially small population. Sightings of 44 groups indicated preference for shallow-water shelf habitat with sea surface temperature between 27.4°C and 30.2°C. Frequent observations were made of lunge feeding, possibly on zooplankton. Observations of four mothers with young calves, and recordings of a song-like vocalization probably indicate reproductive behaviour. Social organization consisted of loose aggregations of predominantly unassociated single individuals spatially and temporally clustered. Photographic recapture of a female re-sighted the following year with a young calf suggests site fidelity or a resident population. Our results demonstrate that the species is a tropical whale without segregation of feeding and breeding habitat, and is probably non-migratory; our data extend the range of this poorly studied whale into the western Indian Ocean. Exclusive range restriction to tropical waters is rare among baleen whale species, except for the various forms of Bryde’s whales and Omura’s whales. Thus, the discovery of a tractable population of Omura’s whales in the tropics presents an opportunity for understanding the ecological factors driving potential convergence of life-history patterns with the distantly related Bryde’s whales.

Description: Assessing the movement patterns and key habitat features of breeding humpback whales is a prerequisite for the conservation management of this philopatric species. To investigate the interactions between humpback whale movements and environmental conditions off Madagascar, we deployed 25 satellite tags in the northeast and southwest coast of Madagascar. For each recorded position, we collated estimates of environmental variables and computed two behavioural metrics: behavioural state of ‘transiting’ (consistent/directional) versus ‘localized’ (variable/non-directional), and active swimming speed (i.e. speed relative to the current). On coastal habitats (i.e. bathymetry 〈 200 m and in adjacent areas), females showed localized behaviour in deep waters (191 ± 20 m) and at large distances (14 ± 0.6 km) from shore, suggesting that their breeding habitat extends beyond the shallowest waters available close to the coastline. Males' active swimming speed decreased in shallow waters, but environmental parameters did not influence their likelihood to exhibit localized movements, which was probably dominated by social factors instead. In oceanic habitats, both males and females showed localized behaviours in shallow waters and favoured high chlorophyll- a concentrations. Active swimming speed accounts for a large proportion of observed movement speed; however, breeding humpback whales probably exploit prevailing ocean currents to maximize displacement. This study provides evidence that coastal areas, generally subject to strong human pressure, remain the core habitat of humpback whales off Madagascar. Our results expand the knowledge of humpback whale habitat use in oceanic habitat and response to variability of environmental factors such as oceanic current and chlorophyll level.

Description: The function of song has been well studied in numerous taxa and plays a role in mediating both intersexual and intrasexual interactions. Humpback whales are among few mammals who sing, but the role of sexual selection on song in this species is poorly understood. While one predominant hypothesis is that song mediates male–male interactions, the mechanism by which this may occur has never been explored. We applied metrics typically used to assess songbird interactions to examine song sequences and movement patterns of humpback whale singers. We found that males altered their song presentation in the presence of other singers; focal males increased the rate at which they switched between phrase types ( p = 0.005), and tended to increase the overall evenness of their song presentation ( p = 0.06) after a second male began singing. Two-singer dyads overlapped their song sequences significantly more than expected by chance. Spatial analyses revealed that change in distance between singers was related to whether both males kept singing ( p = 0.012), with close approaches leading to song cessation. Overall, acoustic interactions resemble known mechanisms of mediating intrasexual interactions in songbirds. Future work should focus on more precisely resolving how changes in song presentation may be used in competition between singing males.

Description: Blue whales produce regionally-distinct songs. In over a decade since McDonald and colleagues published a summary of biogeographic differences in blue whale songs worldwide, multiple new publications have explored the seasonality and distribution of those songs. We review the spatial and temporal occurrence of previously-defined song types and report several new blue whale song types. At least thirteen songs believed to be produced by blue whales are now known worldwide, five more than reported in the previous review. In the North Pacific Ocean there are three blue whale songs: the well-studied Northeast Pacific song, the Central North Pacific (previously called Northwest and North Pacific) song, and a new song recorded off Hokkaido, Japan. There is spatial overlap of the Northeast Pacific and Central North Pacific songs in the Gulf of Alaska. Similarly, the new song co-occurs with the Central North Pacific song off Hokkaido. Only one blue whale song occurs in the North Atlantic. At least nine songs are present in the Southern Hemisphere. The Antarctic blue whale song is the most widely distributed, occurring in the Southern Ocean as well as seasonally extending into the other oceans of the Southern Hemisphere. The Indian Ocean has the largest variety of blue whale songs, with new data suggesting the Southwest Indian Ocean song should have type locality Madagascar, with Diego Garcia possibly another song-type. Southeast Pacific contains two distinct, co-occurring songs. We report a new song in the South Atlantic, near South Georgia Island, that also occurs seasonally off Ascension Island. Occasionally blue whale songs were recorded outside of their reported range, indicating individuals at times roam more broadly. However, this is not a common occurrence. This new information and finer details of occurrence will enable further development of hypotheses for blue whale population structure based on acoustics.