This Whiskered
Tern breeding colony was discovered by members of the Bairnsdale and District
Field Naturalists Club in early December 2016, at Lake Omeo located near
Benambra in East Gippsland’s high country, when members visited the lake to
check on some rare plants.
For more
information about Whiskered Terns please refer to two previous posts:
Lake Omeo
is about 700 metres above sea level. At the current knee-deep water depth, the
lake is about 5km long and nearly 2km wide at its widest point. The lake has no
outlet as the original drainage to Morass Creek was cut off by faulting and
block tilting many thousands of years ago. The Lake is normally dry, however
after good rains it can have sufficient water depth to support many water birds
and breeding events such as the Whiskered Terns now breeding there. In the
past, the lake sometimes even had enough water depth to support water sports
such as water skiing and sailing, but it only fills to that extent on very rare
occasions these days.
Please click on photos to enlarge.
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Looking towards the north-eastern end of Lake Omeo – Benambra township is on the
right-hand side of the photo. The peaks in the background are The Brothers.
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Whiskered
Terns are colonial breeders and usually breed in shallow marshes and flooded
grassland where aquatic insects are numerous. They are nomadic in Australia and
are quick to exploit flooded areas along inland rivers. Lake Omeo lies just
north of the Dividing Range at the head of the Murray River catchment.
It is
possible the Whiskered Terns travel between the Gippsland Lakes, where they are
often found in large numbers during inland droughts, and the Murray Darling
Basin (MDB) by flying up the Tambo River, crossing the Divide at a low point
near Benambra, and then flying on down the Mitta Mitta River, across Lake
Dartmouth and beyond. However, in doing so they seem to have noticed Lake Omeo
and taken advantage of the rare water and breeding opportunity there even
though the MDB currently has lots of water following good inland rains in 2016.
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| Looking south from out on the Lake – the peaks in the middle background are The
Sisters which are on the Great Divide – water falling on the other side of the
Sisters runs into the Tambo River which discharges to the Gippsland Lakes and
then Bass Strait. |
In early December
2016, 60 to 70 breeding pairs were reported to be on nests with eggs in the
middle of the lake and more birds were building nests. When I made my first
visit to the Lake on the 4th of January 2017 there were no nests in
the middle of the lake. This breeding attempt had clearly failed. However, the
birds had made a fresh start in more substantial aquatic vegetation near the NE
end of the lake.
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| Looking south across Lake Omeo and the aquatic vegetation where the Whiskered
Tern breeding colony is located. |
It is hard
to estimate the number of Whiskered Terns present and the number of nests. However
my conservative guestimate on the 4th of January was 250 adult birds
with 100 breeding pairs on about 100 nests. Of about 30 nests inspected, only
two had one just- hatched chick. Given an incubation period of 18 to 20 days, egg
laying for the new breeding event must have commenced on about the 12th
of December. Hatching is synchronous, that is, incubation starts after the last
egg is laid and the chicks all hatch at about the same time.
While
Whiskered Terns are colonial breeders each pair defends a small territory
around their nest, so nests are spread across a large area. The nests were
located in a species of rush and the same plant was used to construct the
nests.
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| Whiskered Tern nest - this one is more substantial and more protected than many
of the other nests. |
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| Side view
of another nest – some nests are anchored in the surrounding vegetation while
others float while being constrained laterally by the rushes. |
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| One of
the 30 nests checked on the 4th of January. The egg on the nest has
a small hole – the start of another chick working its way out of the egg. |
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| This
was the other just hatched chick (4/01/17). |
Hoary-headed
Grebes apparently often nest in association with Whiskered Tern colonies and
this was the case at Lake Omeo.
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| Hoary-headed Grebe nest – with egg covering vegetation removed for the photo
and then carefully replaced. |
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| The
Hoary-headed Grebes were very secretive around their nests – I never saw one either
on a nest or leaving a nest. |
Both Whiskered
Tern parents share nest building, incubation and care of the chicks. A hide was
used to photograph adult birds on the nest because even though they leave the
nest on approach, they soon return once you are concealed in the hide.
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| Pair
on a nest. |
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| Adult
on a nest. |
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| This
bird has just flow in to the nest and is about to settle on the eggs. |
Partner
birds would stand on the nest beside the incubating bird or rest nearby.
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| At
first I thought this bird was collecting nest material. It tried to lift two
reeds. |
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| Then
it tried to lift one reed. |
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| In the
end it just perched on the floating reeds – I suspect it was the partner to one
of the birds on a nest I was photographing. |
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| Adult
Whiskered Tern in breeding plumage. |
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| Adult
Whiskered Tern in breeding plumage. |
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| Non-breeding
Whiskered Tern – most of the Whiskered Terns at Lake Omeo were in breeding
plumage. |
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| Flock
of Whiskered Terns – I could not work out why they were massing above this
point on the Lake – they did not look to be feeding? |
There are
49 birds in the photo above and there were probably another 15 birds outside of
the frame making 64 birds altogether.
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| A
slightly cropped version of the photo above – the WT’s are all looking down –
but what were they so focused on? |
Another
visit to Lake Omeo was made on the 22nd of January to see how the
breeding colony was progressing. What a difference 18 days makes! There were
still a few birds on nests with eggs, however most of the eggs seen on the 4th
of January had hatched and there were many young birds ranging from recently
hatched unfledged young to fully fledged flying young. This was good to see as
it meant, unlike the early December breeding attempt that had completely failed,
this attempt had successfully produced many young.
On one
count, there were at least 50 birds flying this way and that across the SW half
of the lake searching for aquatic food. However Whiskered Terns also hunt over
dry land for insects and other small prey such as skinks. One bird was spotted
with a small skink in its bill flying around the breeding colony looking for
its young. Another bird was seen with a fish.
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| Whiskered Tern with a skink – probably taken in the dryland grazing paddocks beyond
the lake. |
The colony
is a very noisy place as birds come and go with food for young. When they
approach with food there is a lot of calling from both parents and young to
locate each other for food delivery. The young birds appear to be very mobile
both pre-flight swimmers and fledged flyers. Once chicks hatch they are quick
to move away from the nest and into the shelter of the rushes – they would be
easy standout prey on the nests.
Nesting
birds and their young are very vulnerable to predation and nesting in colonies
is one way to counter predation. Only one raptor was seen while at the colony,
a juvenile Swamp Harrier. Swamp Harriers are very effective hunters in wetland
habitats and young water birds are often easy prey. To counter this threat, the
Whiskered Terns band together to aggressively mob threatening intruders such as
Harriers and birdwatchers.
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| This
juvenile Swamp Harrier was hanging around the Whiskered Tern breeding colony
and was no doubt preying on young Terns. |
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| At one
point the young Harrier flew across the breeding area and was immediately
attacked by 15 or so Whiskered Terns – on this occasion the Harrier was driven
out of the area. |
The young
were very wary. The non- flying birds could swim well and took shelter in the
reeds, leaving their nest almost immediately as nests are very visible to
predators. The fledged flyers were also wary and took flight early, not
allowing close approach for photos. I am sure the parents warn the young birds
to hide or fly at our approach.
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| Chick
hiding in the reeds. |
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| Another chick hiding in the reeds. |
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| An
older chick with developing wing feathers held up out of the water while swimming
strongly. |
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| These
three juveniles were probably siblings and all could fly. From hatching these
young ones have fledged to the point of being able to fly in about 18 days.
They are still showing some down around the head and face. |
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| One
juvenile has flown, the second has just taken off and the third bird was not
far behind its siblings. |
The period
from the start of incubation to a fledged flying bird, can be as short as 36
days. For birds that respond opportunistically to flooding events, a short time
to raise young is an evolutionary advantage.
It was very
interesting to observe a Whiskered Tern breeding colony in East Gippsland as
these events are uncommon in our area and certainly are rarely recorded.
