DDt causes thin eggshells in some birds, kills others outright. This link is very informative and comes from a sound source.
http://www.stanford.edu/group/stanfordbirds/text/essays/DDT_and_Birds.html
There are more pages there too if you follow the links at the bottom of the page.
http://www.stanford.edu/group/stanfordbirds/text/essays/DDT_and_Birds.html
There are more pages there too if you follow the links at the bottom of the page.