I have a particular fondness for condors, so when I see an article about California Condors published in The Condor (a major ornithology journal), I usually take a quick look. The look in this case was very short, because I am on my way to other things, but I found it interesting enough to mention to you.
Captive bred condors have over the last couple of decades been reintroduced to both southern (Ventura county) and central (Bug Sur) California, and young birds in both places have begun nesting. Their success has been limited, especially around Big Sur, where many of the egg shells have been extremely thin, leading to dehydration of the egg, fragility, etc. Why, you may well ask, should the eggshells be so thin around Big Sur? The suggested answer is that these condors do a lot of feeding on dead sea lions that wash up on the nearby beaches, and those sea lions do a lot of their feeding off southern California, in an area where an old DDT factory used to discharge its wastes into the ocean. DDT, and its breakdown product, DDE, are extremely persistent toxins, and biomagnify. So even though DDT was banned in the US in 1972, the marine ecosystems in that area are still quite contaminated. Algae pick up the DDE, small fish eat many times their weight in algae, bigger fish eat many times their weight in small fish, etc., up the food chain through sea-lions and eventually condors, who get a highly concentrated dose from their picnic on the beach. The Ventura condors don't often eat sea lion, and so don't get so much DDE. The Big Sur condors can see sea lion beaches from their majestically placed release area, and get enough DDE to seriously impair their reproduction. This of course is not the first time they have had this problem, but it is a reminder that DDT, while banned, is far from gone.