knowledge, no data on mirex levels in Caspian Terns were available at the time this article was written. Based on our unpublished 1977 survey. the mirex (and other O C ) levels in Lake Ontario Caspian Tern eggs are 4 to 6 times lower than in Herring Gull eggs from this lake. Any hypotheses on the role of mirex and photomirex in the reproductive failure, behavioural abnormalities and teratogenic effects seen in Lake Ontario fish-eating birds remain unproven, and are not supported by laboratory studies on birds. The direct embryotoxicity of mirex in f-lerring Gulls has recently been ruled out [Gilman et al., J . Wild/. Manage., 42,477 ( 1978)]. The implication on p 523 that all Herring Gulls from Lakes Superior, Huron and Erie “winter” on or “migrate” to Lake Ontario is simplistic and misleading. Herring Gulls from the more northerly Great Lakes have been shown to move to where open water and food exists [Gilman et a]., J . Wildl. Manage., 41, 458 (1978); Moore, Bird-Banding, 47, 14 1 (1976)l. Thus, Lake Superior and Lake Huron Gulls tend to move to Lake Michigan, Lake Eric and Lake Ontario during the winter. The Herring Gulls in the southernmost Lakes
LETTERS Pesticides-mirex Dear Sir: The pesticide report entitled, “The Rise and Fall of Mirex,” ( E S & T , May 1978, pp 520-528), makes extensive reference to residue levels and biological effects of mirex in birds. The report is a commendable effort to synthesize the existing information on mirex in the Great Lakes, but obviously suffers from the lack of a proper biological insight. Most of the data on residue levels in birds were contributed by the Canadian Wildlife Service (CWS) to the Task Force on Mirex (TFM, 1977). We therefore wish to take issue with some of the interpretations and to point out the most significant errors. Most misleading is the photograph on page 523. There is no evidence that abnormalities such as crossed bills are caused by mirex. The adult bird and chick are not Herring Gulls as implied; they are Caspian Terns. To our
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are less mobile in winter. As a consequence, there is less interchange between Lake Michigan and Lake Ontario populations than Lake Superior and Lake Ontario populations. A Lake Superior egg is therefore more likely to contain mirex than a Lake Michigan egg. I n the discussion on mirex levels in falcons ( p 525), the gyrfalcon feeds on “resident,” not “resistant” herbivores. The residue data (Table 3) represent mirex levels entirely in Western (Saskatchewan and Alberta) and Northwestern Arctic falcon eggs. There were no eggs taken from “Eastern” Canada. The likelihood of falcon prey species having resided at any time in the vicinity of Lake Ontario is relatively remote. The correct reference for “Norstrom et al. ( 1 976)” is Norstrom, R. J., D. J. Hallett and R.A. Sonstegard, J . Fish. Res. Board Can., 35, 1401 ( 1 978). D. B. Peakall R . J. Norstrom D. J. Hallett G. A. Fox A. P. Cilman hational Wildlife Research Centre Ottawa, Ontario K I A OE7 Canada
