The energetics of pursuing, capturing and digesting prey also needs to be
taken into account by the predator.
A potential prey species might be locally abundant, but the predator may
have to spend a lot of energy to chase and eventually capture it. Therefore,
a predator needs to select prey items that require the expenditure of as
little energy as possible to capture and digest, and which provide maximum
nutritional and energy benefits.
If gulls were a common food source for WBSEs, my guess is that a WBSE
soaring overhead or nearby would cause the gulls to take to the skies to
escape potential danger. Gulls are quite aerobatic and, when they are in a
flock, I would imagine it would be difficult for a WBSE to capture one
quickly. Therefore, there is a risk of the WBSE using up too much energy to
capture a gull in comparison with the energy it would gain from consuming
one (if it is lucky enough to capture a gull).
I remember many years ago observing a Peregrine Falcon harassing a small
flock of airborne Welcome Swallows at Kanidal Beach (Eyre Bird Observatory).
The swallows swooped and swirled in a tight flock, and just aerobatically
out-manouevred the diving Peregrine. This continued for several minutes
before one swallow made the fatal error of separating from the flock and
flying in a straight line out over the ocean. Seconds later, it was taken
successfully by the Peregrine. The question that immediately came to my
mind: was it worth the Peregrine doing this? I don't know, but it would
have spent a lot of energy harassing the swallows and I suspect the reward
(one swallow) did not provide much net energy and nutritional benefit in
return.
Stephen Ambrose
Ryde, NSW
-----Original Message-----
From:
On Behalf Of Nikolas Haass
Sent: Monday, 25 June 2012 7:28 PM
To: patrick appleton;
Subject: RE- SEA EAGLE CATCHING SEAGULL IN MID AIR
Patrick,
A basic rule in ecology is that the prey controls the predator, not the
predator the prey.
In other words: Much prey - good time for the predator.Shortage of prey -
bad time for the predator.
If predators would control their prey, this cycle wouldn't work.
Unfortunately there are exceptions; certain species in man-made or
man-influenced habitat and - of course - man itself...
In other words again: There are White-bellied Sea-eagles around as long as
there is abundance of its prey. It is not the White-bellied Sea-eagles who
reduce their prey - it is us!
I hope the real ecologists out there are not going to punish me for this
very simplified statement!
Cheers,
Nikolas
----------------
Nikolas Haass
Sydney, NSW
________________________________
From: patrick appleton <>
To:
Sent: Monday, June 25, 2012 4:57 PM
Subject: RE- SEA EAGLE CATCHING SEAGULL IN MID AIR
When Sea Eagles snatch up swan cygnets I momentarily hate them and threaten
to cancel my subscription to Sea Eagle Cam but I had no idea they'd feed on
seagull.
So why then, are there so few Sea Eagles and an abundance of Gulls????
ALSO:
The Black Swan Communal Nesting Site at Paynesville, (Gippsland Lakes) has
its first occupants for this season with 3 nests occupied. At nest #1 both
mum & dad were in the water today and I saw a white (???????) seabird swoop
down and steal an egg and started eating the yellow contents in about 6
inches of water by the lake edge. Dad came by and after having a taste of
the contents himself, washed the contents out of the egg shell and threw it
into deeper water.
Obviously my first question is, What is the name of the white seabird that
looks like a plain seagull on steroids, (about twice the size) like a dwarf
Albatross ????
Also, why do black swans leave their nests to chastise harmless juvenile
swans yet pay no attention to egg stealing preditors ???
Is it an experience thing? I notice the other two nests are never left
unattended.
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