The migrations reported here (up to 8461
km minimum travelling distance)
are the longest movements documented for any mammal. The longest previously known
migration was reported by Stone et
for a humpback whale that moved between the Antarctic
Peninsula and Colombia (7878
km according to our method; their reported
km is probably an overestimate).
These trans-equatorial migrations between Antarctica and Central America are common
for at least part of the humpback whale population in the eastern South Pacific.
During this study, whales were regularly sighted off Panama and Costa Rica in the
austral winter as far north as 11°
N. Group composition
(mother/calf pairs) and behaviours (competing males and singing males) were
indicative of an area used for calving and mating. This area is probably an
extension of the wintering area off Ecuador and Colombia (). The combined extent of these wintering areas () may be a result of whales migrating
further north to Central America due to space limitation or other density-dependent
Another unique aspect of this area is the spatial overlap with whales from the
Northern Hemisphere. The work we have conducted off Central America during the
boreal winter season (December–April) since 1996 indicates that this is
also a wintering area for eastern North Pacific humpback whales migrating from
feeding areas off California (Calambokidis
et al. 2000
). In fact, anecdotal whale sightings
have been reported monthly off Central America (Rasmussen 2006
), although the population identity of animals seen during
the non-peak occurrence months remains undetermined. Eastern North and South Pacific
populations share genetic traits indicating a trans-equatorial exchange, probably
off Central America (Medrano-González
et al. 2001
The climatological August SST in the Central American wintering area is 28°C
(electronic supplementary material). Temperatures between 24 and 28°C were
reported at other humpback whale wintering areas (Dawbin 1966
; Herman & Antinoja
; Whitehead & Moore
), consistent with our global SST analysis (; electronic supplementary material). Coastal
upwelling and cold tongue development during the austral winter result in cool
surface waters extending from the South American coast into the eastern equatorial
Pacific, such that SSTs greater than 24°C only occur north of the equator
( and ). This implies that humpback whales in the eastern South
Pacific need to migrate farther north to wintering areas off Ecuador, Colombia and
Central America. This pattern is observed again off the western coast of Africa,
where an anomalously northerly wintering area for eastern South Atlantic humpback
whales (Findlay et al.
; Walsh et al.
; Van Waerebeek et al.
) coincides with the occurrence of coastal upwelling and an
equatorial cold tongue (). Thus,
while the availability of suitable reproductive habitat at the wintering areas is
important at the fine scale (e.g. Ersts &
& Haase 2005
), water temperature influences their distribution at
the basin scale.
Our analysis shows that worldwide humpback whale wintering areas are found in warm
coastal waters irrespective of latitude. In the ongoing debate on the reasons for
migration, this result supports previous ideas linking temperature at the wintering
areas to energetic strategies without the need to invoke killer whale avoidance.
suggests that, as in some
terrestrial mammals, energy conserved during offspring development can be devoted to
growth, leading to larger size and increased reproductive success in adulthood.
Thus, the temperature regime at the wintering areas, regardless of distance to the
feeding areas, probably constitutes a major selective force driving humpback whale