It may be that the birds which controlled the ticks had died of thin shelled egg syndrome which is caused by DDT. PCB, another chlorinated biphenyl, might be a culprit as well. We know they caused the outrigh death of many seabirds.
gardenofeaden.blogspot.com
If you live in a tick area and have a large yard, get a few guinea fowl and train them to roost in a predator safe place. They are excellent at controlling ticks.
birdlife.org
doityourself.com
"Anderson notes that DDT and DDE levels in nature have been falling for decades. Populations of bald eagles, peregrine falcons, ospreys, and brown pelicans have all bounced back. In 1969, researchers reported finding total DDT accumulations ranging from 5,000 ppm to 2,600 ppm in the fat of North American peregrine falcons. Today, one would typically find 50 ppm in raptors, according to Anderson. Such body burdens would yield only about 2.5 ppm in eggs. Anderson notes that there appears to be a threshold of one to three ppm for DDE in eggs below which there is no eggshell thinning in even sensitive bird species. Dusting DDT on the walls of houses in developing countries to control for mosquitoes seems unlikely to cross that threshold for birds."
"Polychlorinated biphenyls (PCBs) are worldwide chemical pollutants to which bird populations may be especially sensitive. Even at low concentrations, PCBs cause neurological damage and mimic estrogen activity, thereby altering sexual development and reproduction. Hormonal balance plays a key role in bird song, so it might be possible to monitor PCB exposure by studying songbirds. To test this hypothesis, researcher Sara DeLeon recorded songs and collected blood and feather samples from Black-capped Chickadees and Song Sparrows along a gradient of PCB contamination along the Hudson River in New York. Her preliminary results suggest that nonlethal levels of PCBs in the environment do affect bird song, a finding with implications for wild birds in polluted landscapes." |
