 DDT pollution in the environment was a major cause of decline of brown pelican populations in North America in the 1950s and 1960s . It entered the oceanic food web , contaminating and accumulating in several species , including one of the pelican ’ s primary food fish – the northern anchovy . Its metabolite DDE is a reproductive <unk> in pelicans and many other birds , causing eggshell thinning and weakening , and consequent breeding failure through the eggs being accidentally crushed by brooding birds . Since an effective ban on the use of DDT was implemented in the US in 1972 , the eggshells of breeding brown pelicans there have thickened and their populations have largely recovered . 
