Tracking Ocean Wanders (PDF, 5 MB) - BirdLife International

waters. Main foraging areas were located over the
continental shelf and slope south to 55ºS. During chickrearing,
albatrosses mixed two strategies, short trips over
the surrounding waters in southern Chile (similar to
distribution during brooding), representing up to 90% of
total trips, with long trips to central Chile (similar to those
made during incubation) and Antarctic waters, mainly
along the continental shelf and slope of the western
Antarctic Peninsula. Despite the difference in trip
characteristics between breeding stages, Black-browed
Albatrosses tracked from Diego Ramirez foraged mainly
over Chilean territorial waters, especially inside the EEZ
waters during breeding, with very occasional forays into
Argentine Patagonian Shelf waters.
During incubation, birds tracked from Isla Ildefonso
show a similar distribution to Diego Ramirez, with
concentrations occurring off the Arauco Gulf, Los Chonos
Archipelago (45ºS) and southern Chile (50–57ºS). This
result is similar to that between Falkland Island (Malvinas)
colonies during incubation.
There is a strong interaction between breeding
albatrosses and fishing vessels, which produce food through
offal discards and cause mortality by incidental capture
(Arata and Xavier 2003, Moreno et al. 2003). Thus, it seems
likely that fishing boats could affect the normal distribution
patterns of Black-browed Albatrosses in southern Chile and
reduce inter-colony competition by food, allowing greater
than normal levels of foraging range overlap.
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Tracking ocean wanderers: the global distribution of albatrosses and petrels – Results
Javier Arata and Graham Robertson
Figure 3.7. Utilisation
distribution maps for
breeding Black-browed
Albatrosses tracked from Isla
Diego Ramirez at different
stages in the breeding cycle.
A. incubating birds
(n=10,103 hrs); B. early
breeding (incubation/
brooding) (n=1,642 hrs);
C. brooding (n=5,367 hrs);
D. post guard (n=6,083 hrs).
(Unable to determine number
of individuals of each
category from dataset, so
sample sizes are only given
in number of hours tracked).
3.1.2 Distribution of breeding birds in relation to sex
Northern and Southern Giant-petrels Macronectes halli
and M. giganteus – South Georgia
Giant-petrels are the largest birds of the family Procellariidae,
weighing about 4–5 kg and with a wingspan of 150–210 cm.
Both sibling species, the Northern Macronectes halli and the
Southern M. giganteus, show a noticeable sexual size
dimorphism in which males are between 16 and 35% heavier
and have disproportionately larger bills than females
(González-Solís 2004). The two species are the dominant
scavengers of the Southern Ocean; males and females of
both species rely mainly on penguin and pinniped carrion,
but complement this diet by taking live seabirds, scavenging
on food waste and feeding on marine prey such as
crustaceans, cephalopods and fish (Hunter 1985).
There is much evidence, from various sources, that both
species of giant-petrels are among the more remarkable
examples of sexual segregation in feeding habits in birds.
Direct observation of feeding habits, diet analysis and stable
isotope heavy metal studies, all suggest clear segregation in
the trophic habits of males and females in both species
(Hunter 1983, Becker et al. 2002, González-Solís et al. 2002b,
González-Solís and Croxall 2005). Such sexual differences
in the type of prey consumed imply a fundamental decision
to direct the searching effort to particular habitats.
This is well demonstrated in the areas exploited by each
sex during the incubation period. In both species most males
engaged in short trips close to the breeding grounds whereas
most females foraged in pelagic waters further away from