s een at 43 nes ts in 1957, were s o s carce that he obs erved the m at only 10 nes ts. Although Mr.
Broley’s death in 1959 terminated this valuable s eries of uninterrupted obs ervations , reports by
the Florida Audubon Society, as well as from New Jersey and Pennsylvania, confirm the trend
that may well make it necess ary for us to find a new national emblem. The reports of Maurice
Broun, curator of the Hawk Mountain Sanctuary, are especially significant. Hawk Mountain is a
pictures que mountaintop in s outheas tern Penns ylvania, where the eas ternmos t ridges of the
Appalachians form a last barrier to the westerly winds before dropping away toward the coastal
plain. Winds s triking the mountains are deflected upward s o that on many autumn days the re is
a continuous updraft on which the broa d-winged hawks and eagles ride without effort, cove ring
many miles of their southward migration in a day. At Hawk Mountain the ridges converge and
so do the aerial highways. The result is that from a wides pread territory to the north birds pas s
through this traffic bottleneck. In his more than a s core of years as cus todian of the s anctuary
there, Maurice Broun has obs erved and actually tabulated more hawks and eagles than any
othe r A merican. The peak of the bald eagle migration comes in late August and early
Septe mbe r. Thes e are ass umed to be Florida birds , returning to home territory after a s ummer
in the North. (Later in the fall and early winter a few larger eagles drift through. These are
thought to belong to a northe rn race, bound for an unk nown wintering ground.) During the firs t
years after the sanctuary was established, from 1935 to 1939, 40 per cent of the eagles
obs erved we re yearlings , eas ily identified by their uniformly dark plumage. But in recent years
thes e immature bi rds have become a rarity. Betwee n 1955 and 19 59, they made up only 20 per
cent of the total count, and in one year (1957) there was only one young eagle for every 32
adults. Observations at Hawk Mountain are in line with findings els ewhere. One s uch report
comes from Elton Fawks, an official of the Natural Resources Council of Illinois. Eagles—
probably northern nes ters—winter along the Mississippi and Illinois Rivers. In 1958 Mr. Fawks
reporte d that a rece nt count of 59 eagles had included only one immature bi rd. Similar
indications of the dying out of the race come from the world’s only s anctuary for eagles alone,
Mount Johns on Is land in the Sus quehanna River. The island, although only 8 miles above
Conowingo Da m and about half a mile out f rom the Lancas ter County s hore, retains its
primitive wildnes s. Since 1934 its s ingle eagle nes t has been under obs ervation by Profes s or
Herbert H. Beck, an ornithologis t of Lancas ter and cus todian of the s anctuary. Between 1935
and 1947 us e of the nes t was regular and uniformly s uccess ful. Since 1947, although the adults
have occupied the nes t and there is evidence of egg laying, no young eagles have been
produced. On Mount Johns on Is land as well as in Florida, then, the s ame s ituation prevails—
there is s ome occupancy of nes ts by adults , s ome produc tion of eggs , but few or no young
birds. In s eeking an explanation, only one appea rs to fit all the facts. This is that the
reproductive capacity of the birds has been s o lowered by s ome envi ronme ntal agent that
there are now almost no annual additions of young to maintain the race.
Exactly this sort of situation has been produced artificially in other birds by various
experime nte rs , notably Dr. James DeWitt of the United States Fis h and Wildlife Service. Dr.
DeWitt’s now classic experiments on the effect of a series of ins ecticides on quail and
pheas ants have es tablis hed the fact that expos ure to DDT or related chemicals , even when
doing no obs ervable harm to the pare nt bi rds , may s erious ly affect reproduc tion. The way the
effect is exerted may va ry, but the end result is always the same. For example, quail into whose
diet DDT was introduced throughout the breeding s eas on s urvived and even produced normal
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