pairs in Europe. Conservation status - a
conservation priority in some parts of the
around the Arctic including many islands, native
to the far north usually found in treeless tundra.
Size: 3 to 8kg (6.5-17
lbs), 75 to 110 cm long (2.3-3.5 feet) including
a tail of around 30cm (12 inches), 20 to 30cm
(9-12 inches) tall at the shoulder, females
slightly smaller than males.
What are Arctic
Terns like? How are they adapted to
Arctic Tern is a member of a very exclusive animal
club, it can be found at different times at both poles.
The polar regions are areas of very high
seasonal productivity. Very long day length
with up to 24 hours daylight in the summer
depending on the distance to the pole. This
means that photosynthetic productivity
(plant growth) is in overdrive, especially
in the sea which leads to an abundance of
other potential food a little further along
the food chain which is then available to
larger animals such as birds like terns.
Such is this abundance of seasonal food, it
is actually worth the effort for terms to fly the
length of the planet to take advantage of
the Antarctic summer after spending the
Arctic summer having partaken of its abundance.
They breed in the Arctic and use Antarctica
as the wintering grounds (though it is the
The flying abilities of these birds are
amongst the most astonishing of any. They
have a length of a little over 30cm (a
foot), a wingspan of less than a meter
(about two and a half feet) and a weight of
around 100g (3.5oz, or a little less than a
quarterpounder burger). Despite this, they have
been measured at flying up 90,000 km (nearly
56,000 miles) a year.
Arctic terns have a very particular and
extreme lifestyle, all the more surprising
when you realise how small they are, they have a number of anatomical,
behavioural and physiological adaptations that
allow them to survive successfully.
- Very high
metabolic rate (physiological)
- Many polar and cold climate birds deal
with cold temperatures by consuming and
burning food to generate heat from
within. In order to do this they have to
consume high energy, easily and quickly
digestible food. The fish and oily krill
and other prey that terns feed on
provide the readily accessible energy
that enables them to live their
- Dive bomb other
animals that approach the nest, aiming
at the head (behavioural) -
Whether a potential predator or just
some big clumsy animal that might
trample the nest, eggs and chicks, they
all come in for the same treatment.
Arctic terns dive repeatedly at any
animal (including man) that they think
represents a threat. They call out in
alarm and repeatedly attack from behind
the head so they have maximum
disorientation effect and are less
likely to be harmed themselves. They
keep going as long as they feel
threatened and stop when the threat is
sufficiently far away. Often you will
have no idea where the nest actually is
other than somewhere near where you
were. A frantic term attack can leave
even a polar bear with bloody wounds to
- Nests in
colonies with other birds
(behavioural) - This maximizes the
effectiveness of the defensive
dive-bombing behaviour with many birds
involved at the same time.
- Flies from the
Arctic to Antarctic and back again every
year (behavioural) - Arctic Terns
nest in the Arctic during the summer,
when their young have fledged and become
independent, they then fly to Antarctica
(including the juveniles) where they
winter during the Antarctic summer
before flying back again to the Arctic
to breed the following year. They do
this to take advantage of food
abundances at the peak times of year and
to avoid food shortages at other times.
Fantastic fliers - as you might imagine
- Shaped with tail feathers that can be
spread wide or pulled into a narrow dart
to change aerodynamics in flight for
covering distance or hovering and diving
while feeding. Hollow bones for
lightness. Able to sleep on the wing
during migrations. Short legs that aid
an aerodynamic shape in the air but make
the birds rather clumsy on the ground.
What do Arctic
Terns eat? How do they live?
Distribution range of
the Arctic Tern, nesting region in red
Andreas Trepte -
licensed under CC BY-SA 2.5
- Arctic terns
are opportunistic feeders, they
feed on fish and larger zooplankton such
as krill especially when in Antarctica.
They catch their prey by seeing them
from the air, searching and hovering
much like a hawk does on the land and
then diving to catch them.
- They nest and
rear their young all around the Arctic,
though mainly fly south along an
Atlantic route before spreading out
again once in Antarctica.
- The most
remarkable thing about Arctic Terns is
that their annual migration that is
about 70,900km (44,000 miles).
This has recently be proven by attaching
trackers onto birds and is around twice
the previously thought distance. The
reason is that the birds follow the
prevailing wind patterns that carry them
along, though not taking the most direct
- They stop over
in an area of upwelling and high
productivity in the North-Atlantic for
around 25 days when flying south.
It takes them about 3 months on the
journey south, but only around 40 days
to fly back north again, mainly due to
the strength of the prevailing winds.
- They arrive in
the north in April/May, mate, nest and
rear their young. They leave again in
July/August to reach Antarctica in
November where they stay until
February/March. Both the Arctic
and the Antarctic have 24 hours daylight
in mid-summer and Arctic Terns are in
both places in mid summer. They are most
probably the animal that experiences the
most daylight of any on the planet.
Arctic tern migration project
Tern on ground - picture courtesy
Andreas Trepte -
licensed under CC BY-SA 2.5