The study by Boellstorff et al. (1985), documented the decline in DDT + DDD, and dieldrin at Lower Klamath and Clear Lake National Wildlife Refuges (NWRs) in pelican eggs between 1969 and 1981, but showed no change in DDE or total PCBs over time.  There was a difference in amounts of DDE residues between the grebe eggs and white pelican eggs.  The PCB residues in Lower Klamath and Clear Lake pelican eggs differed suggesting differences in overwintering and/or migration.   Shell thinning in pelican eggs declined during this period but remained greater than pre-1947 values.  The continued concentrations of DDE in the birds was attributed to the use of dicofol (Keltane) in the Central Valley of California, a product contaminated with 6 to 9 percent DDE.  Nineteen of 38 pelicans probably died from endrin or additive effects of dieldrin + endrin, with greater than 0.8 ppm w.w. in their brains, similar to mortalities at Stillwater NWR.  Since endrin was unlikely used near Stillwater or Klamath Basin, it was probably derived from overwintering grounds or along the northward spring migration.

Learn more by reading the following full report:

Boellstorff, D.E., H.M. Ohlendorf, D.W. Anderson, E.J. O'Neill, J.O. Keith, and R.M. Prouty. 1985. Organochlorine chemical residues in white pelicans and western grebes from the Klamath Basin, California. Arch. Environ. Contam.Toxicol. 14:485-493.

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