Thread: Counting frogs
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Old 20-03-2003, 12:08 AM
Kay Easton
 
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Default Counting frogs

In article , Martin Sykes
writes
"Kay Easton" wrote in message
...
Does anyone have any idea how to count the frogs in a pond?

Drop a grass snake in the pond. *all* the frogs will jump out. :-)

For example - I counted 36 frogs in the pond today - does that mean I
have 36 frogs? Or have I got nearer 50?

More seriously, apart from wondering why it's important,


It's not importnat, but it's interesting.

depending on how
long you spent looking you probably counted the same frog more than once.


No, no - this was 36 simultaneous frog heads sticking out - I could see
them all so I know that none of them moved.

Your presence there probably made them dive and pop up somewhere else. The
act of observation changes what you are observing.


I approached very slowly! None of them dived. All but 5 vanished when a
kitten appeared, though.

As a rough guide, if you knew what percentage of its time a frog stayed on
the surface on average and how many frogs on average were visible at any one
time then the total number of frogs would be average visible/percentage of
time visible. So if on average there are 10 visible at any one time and they
spend only 25% of their time on the surface then you've got 40 frogs give or
take. The percentage time on the surface could be found if you've got one
easily identifiable frog you could time.


They all look the same to me ;-)


can one tell form how much spawn there is? Does each female lay one
batch or more than one batch - eg if I have 20 batches of spawn have I
got 20 females or could it have been laid by,say, 5 females?


I'm pretty sure they can lay more than one batch. This is only an indication
of female numbers though and is no guide to the number of males.


Oh, quite, I realise that - that's why I asked my third question!

However, I
think frogs can change sex from male to female depending on the temperature
so it's probabably possible to work out the likely ratio of female to male
at a given temperature.

How many females does each male mate with? I presume once he's
fertilised one batch of eggs, he won't just sit on the sidelines, he'll
see if he can find another female.


A male will try and mate with anything that moves.


I don't think it has to move! One of ours was clasping the pipe to the
pump!


--
Kay Easton

Edward's earthworm page:
http://www.scarboro.demon.co.uk/garden/