During winter time, even though we have great whale watching tours and
encounters we can’t forget a very good friend of us, the Cory’s shearwater or
the ‘cagarro’ as we call them in Portuguese. This beautiful marine birds start
accompanying our tours since middle spring to middle autumn, their fly is very
special as they enjoy to touch with their wings the surface of the ocean and
they lead us very often to different species of dolphins (mainly common and
also a summer time species the spotted dolphin).
Let’s now learn a bit more about this very special species: who they are,
which their main characteristics are, how their migration routes are and what the
threats they face nowadays.
We have compiled some information about this
birds, as we think they deserve a bit of attention, even though they are not
cetacean this is a very attached species to our whale watching tours.
Who are these Cory’s shearwaters?
It is a very symbolic migratory seabird of the Azores, as it covers the
world’s largest breeding population of the species (Fig 1). They live in the
open ocean, ranging from neritic zones (areas with water less than 200 meters
deep) to continental shelves, and only come ashore during the breeding season.
Fig1:
Cory’s shearwater abundance. Graphic by Victor Martin
Their open ocean habitat covers warm waters of that are connected with
high productive ecosystems,
such as ocean fronts,
deep-water springs and continental shelves.
This creates a food source for many marine animals, like the Cory’s shearwater.
This species has a complex system of sounds. The sounds are only
produced during the breeding season, in their breeding colonies. Males only
produce high-pitched tones while the females produce more
deep tones. This sounds have a very particular tone that
can be heard specially at night time close to the cliffs were they nest.
Foto by Mariana Silva
The genus name Calonectris comes from
the classical Greek words kalos,
meaning "Good" and nectris meaning "swimmer". And, as might be
expected, the Cory’s shearwater is a great swimmer! The species has webbed feet
as well as long and straight wings that are adapted to allow the birds to use
the updrafts of wind on the waves to “shear” over the water’s surface (hence
the name “shearwater”).
But, not only the wings are perfectly adapted to
an oceanic lifestyle, the species is also adapted to drink seawater due to the
existence of highly developed nasal tubes. They have desalination glands that
extract and dispose of the salt. This is reason why this birds can spend months
in the ocean without coming back to land. They also have an unusually strong
sense of smell. This is very handy, since they can find their food over large
ocean surfaces and also relocate their colonies.
Cory’s shearwaters and common or spotted
dolphins or even other species like tunas are very often seen around the
Azores, and also on our whale watching tours, all feeding together in a
‘feeding area’ were the dolphins surround the school of fish forcing them to
‘make’ a ball and other species including Cory’s profit of this feast diving
directly into the ball of fish.
The diet of Cory’sshearwaters in the Azores has been studied and found to be very diverse.
Several species of octopus, squid, fish and crustaceans have been found in
their stomach contents. The birds are able to catch these prey by diving up to
15 meters deep using their wings as flippers!
When they are not feeding this birds rest on
the surface of the ocean, creating big island of birds that are just
‘floating', it is something very beautiful just to observe them taking off
using the water as a runway with their legs !!
This marine bird has a “Mediterranean cousin”,
the Scopoli’s shearwater (Calonectris diomedea).
For a long time researchers thought that the
Cory’s shearwater (Calonectris diomedea
borealis) was a subspecies from Scopoli’s (Calonectris diomedea). But now, they are considered by researchers
as two different species.
Although their appearance is very similar, they
still have important differences that result in them being distinguished as a
separate species:
The most important difference is their different
and very marked breeding distribution:
• Scopoli’s shearwater
à Mediterranean distribution: Algeria, Croatia, France, Greece, Italy, Malta,
Spain (excluding the Canary Islands), Tunisia and Turkey.
• Cory’s shearwater à Atlantic distribution: Portugal (including the Azores, Madeira and Berlengas)
and the Canary Islands.
Fig 2: Geographical breading area of Scorpoli’s
and Cory’s shearwater.
Genetics are a very important parameter to indicate if
the species are different or not: figure 3 shows the two different populations based
on genomic differences. The Scopoli's shearwater is shown with a blue colour throughout
the Mediterranean Sea and the Cory's shearwater is shown by a red colour in the
Atlantic Ocean.
Fig 3. Population genetic structure
of Cory’s shearwater. Munilla I.
et. al. (2016)
However, genetic material gets mixed between
both species if one individual travels from one population to another (e.g.
from Baleares Islands to Azores Islands). This event is called gene flow, but in this case the gene
flow is low, allowing us to think that there is not a big hibridation between
the two species.
There is
another characteristic that the researchers use to differentiate the two
different species, the bird song. Even
though they use their special song for the same purposes: simple vocalization
for calls and complex for mating, the sound between the two species is
different, being the one of the Cory’s with three syllables and the Scopoli’s
using two:
Don’t miss
theirs incredible singing! Can you notice the difference?
Written by: Cristina Montoya
The genus name Calonectris comes from
the classical Greek words kalos,
meaning "Good" and nectris meaning "swimmer". And, as might be
expected, the Cory’s shearwater is a great swimmer! The species has webbed feet
as well as long and straight wings that are adapted to allow the birds to use
the updrafts of wind on the waves to “shear” over the water’s surface (hence
the name “shearwater”).
Cory’s shearwaters and common or spotted
dolphins or even other species like tunas are very often seen around the
Azores, and also on our whale watching tours, all feeding together in a
‘feeding area’ were the dolphins surround the school of fish forcing them to
‘make’ a ball and other species including Cory’s profit of this feast diving
directly into the ball of fish.
