Franklin's Gulls and chironomids

[Michael Gochfeld]

Joanna Burger and I were studying Franklin's Gulls in Minnesota. Many 
were killed by colliding with utility wires. Stomach contents contained 
in excess of 1500 chironomids (midges). The colony we studied had about 
40,000 pairs (80,000adults) (my calculator says 1.2E+08/day) or 120 
million per day. The season lasted at least 4 weeks =15.36 billion.

Yet our field observations suggested that the birds which fed constantly 
for many minutes made no dent on the emerging midges. 

I remember windrows of dead creatures on the shore of Great Salt Lake, 
multiple millions (probably billions) of Pelagic Red Crab washed ashore 
at Monterrey. 

But it seems like we are talking about apples and oranges in a way. 
Maybe its like the trout vs shark reproduction. There are some organisms 
including some insects which are highly prolific and are "designed" to 
accept a very high mortality, while others have much lower fecundity and 
are extremely vulnerable to anything which increases their mortality 
even slightly.  In orderwords, doubling the Franklin's Gull population 
might have had no adverse impact on chironomids.  But doubling the 
predation (or zapper mortality) on other species wouldn't be tolerated. 


It would probably be interesting to sort out which LEPS fall into which 
categories.

M. Gochfeld 

 
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