Took a walk along the river on a pretty and quite warm morning – a morning that was way too warm for this time of year, but we’d best get used to it.
However, not everything is bleak for a naturalist, for on top of the electrical transmission tower that is one of their favorite perches was a pair of adult bald eagles.
Twenty years ago these two birds would have been one-third of Pennsylvania’s resident population of bald eagles. At that time there were only three breeding pairs of bald eagles in the state, all in the extreme northwest corner. This year there were at least 277 nesting pairs in the state and a possibility (probability?) of other nests that have not been reported.
Why the difference? The simplest answer is that DDT was banned. DDT, the all-purpose “miracle” insecticide that came into widespread use following World War II. But, DDT had the side effect of accumulating in the food chain and causing many species of raptors to lay thin-shelled eggs that broke under the weight of the incubating adults.
Unfortunately, bald eagles were quite susceptible to this egg thinning and their population plummeted as fragile eggs broke beneath incubating adults.
I was in graduate school when Rachel Carson’s book Silent Spring, which described the insidious effects of DDT and other pesticides, was published. How well I remember that one of the entomology professors vehemently denounced the book and its author – how wrong he was!
After a while, one of the eagles took of and flew downstream to disappear behind the riverside trees.
Further along, also on a favorite perch was an adult peregrine falcon, one of the pair that has nested on a nearby bridge. They didn’t raise any young this year – the old female was driven off by a younger bird and the young female didn’t nest successfully.
As with bald eagles, peregrine falcon populations were decimated by DDT’s egg-thinning effect. There were no peregrines nesting anywhere in Pennsylvania for decades until deliberate efforts were made to reintroduce the birds.
For a short time in the 1970s I knew an old fellow (he was younger than I am now – how time flies) who reportedly, 30 years earlier, had removed peregrine chicks from a cliff nest to send to a zoo. That cliff remains unoccupied by nesting peregrines as now most peregrines in the state nest on bridges or buildings.
How fortunate we are to have these two wonderful birds back as nesting species in Pennsylvania.