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Fauna Series No. 1
Methods
Fauna of the National Parks
of the United States
PROBLEMS OF HISTORICAL ORIGIN
TREATMENT OF A SPECIES REDUCED TO DANGER POINT (2)
In discussing the problem of a species whose numbers have been reduced to the danger line by the pioneer depredations of man, it is admitted that possibly nothing can be done to bring that animal back to its former status. Yet even this knowledge can not be had without first making a thorough investigation of the question, including, perhaps, experiment with some betterment measures. On the other hand, many species might be brought back if their plights and all the governing factors were sufficiently understood. A temporary program of special protection to bring about recuperation might include securing greater immunity for the young against enemies on the breeding grounds, or augmenting the food supply at a critical period, or some other measure, depending entirely, of course, on the individual circumstances of the case. In any event, every precaution should be taken against endangering the status of any other species while trying to help one; and, always, the special protection must be discontinued just as soon as the species is out of danger.
Trumpeter swan in Yellowstone. – This is perhaps the best example for this type of problem, not only because the number of trumpeter swans in the Yellowstone region was reduced to a few birds but because these represent the entire known breeding stock in the United States.
Though the trumpeter swan (Cygnus buccinator) and the whistling swan (Cygnus columbianus) are so much alike in appearance as to be almost indistinguishable in the field, the first has all but succumbed, while the latter continues to flourish. Comparison of the two forms is valuable in analyzing the present problem.
The whistling swan bred mainly north of the Arctic Circle, its nesting grounds unaffected by civilization. The trumpeter swan bred in Canada and the great interior valley of the United States, where it was subject to every adverse influence, even to the draining of many of the small breeding lakes.
As winter visitants in the south the whistlers were very shy, so that few were taken by gunners. They came down along the coasts and kept to open waters. The trumpeters, on the other hand, were much less wary, frequenting smaller bodies of water and coming in close to the hunters' blinds.
A whistler might weigh 18 pounds; a large trumpeter, 33. Consequently, the trumpeters made more desirable skins and must have been at a premium in the great swan trade of the Hudson Bay Fur Co., which destroyed the bulk of these birds, even to the northern part of their range, long before permanent settlement came along to do the rest.
As a result of all these influences the trumpeter swan nearly passed from the picture. Its present status is as follows:
In Canada : For conservation reasons, the Canadian Government keeps its data on this species a secret. It is known that a few winter in southern British Columbia, but their breeding grounds have not been discovered. They are believed to be in the northern part of the Province, where, if any colony is found out by Indian or prospector, it is sure to be destroyed.
in the United States : Though the trumpeter may possibly occur south of the international boundary in migration, it is gone as a breeding bird except in the immediate Yellowstone region. All recent nesting records are within the park except for two stations – Jackson Lake, Wyo., and Red Rock Lake, Mont.
The latest breeding census made by the survey party in 1931 showed 5 breeding pairs and 10 birds not breeding. The 5 nests are known to have hatched 18 cygnets, of which 5 were certain losses in the summer, leaving a potential crop of 13. Probably there were further reductions before flying time in late fall, and still others before the winter was over. What this means for perpetuation becomes more significant when one takes into account that breeding age is not attained until the fourth or fifth year.
In captivity : Mr. F. E. Blaauw, of Holland, secured five trumpeters over 30 years ago. Though he has been successful with them, his present stock consists of only 10, of which 5 are immature. In the past few years 12 of Blaauw's birds went to the Kellogg Bird Sanctuary at Battle Creek, Mich. It has not been ascertained that these have bred there.
FIGURE 11. – Only the watchfulness of the parents
deprived ravens of a feast on the
four large eggs of this trumpeter
swan nest.
Photograph taken May 30, 1931, at Trumpeter Lake,
Yellowstone, by G. M. Wright.
Wild Life Survey No. 2353
So much for the general picture. What can be done to perpetuate and increase the trumpeter swan in Yellowstone Park ? Report was received in 1929 that a pair on a small lake in the Lamar Valley had failed to raise any young in the four or five summers they had been observed. In the spring of 1930 the survey party found two nests – the one mentioned above and a second on Mirror Plateau. Each clutch was composed of six eggs. Yet there was but one living cygnet by late autumn.
Suspicion fell upon a number of possible enemies, but only one was convicted. A raven broke an egg in the nest on Mirror Plateau and tried to fly off with the embryo. There were frequent raids by the ravens at the other nest, but they were successfully resisted.
Potential enemies of the cygnets were the coyote, otter, horned owl, eagle, and possibly even the badger. Coyote tracks were abundant around the margins of the lakes, and badgers lived all around. The entire swan families frequently took to the land to feed or to cross to near-by ponds, and they would be easy prey at such times. When the cygnets were small, an otter visited the Lamar Lake. Coots within 6 or 8 feet of the otter showed curiosity, but no fear, and were ignored in return. Neither was the swan family hurt. In the fall, when the cygnets were disappearing one by one, an otter family came to stay in the lake for a time. Coot and ruddy duck remains were found in the feces, but no sign of a cygnet. The otters were not proved guilty.
One night in the following summer a member of the party slept at the very edge of the lake so that he might hear any unusual sound. In the morning one cygnet was missing. Horned owls were in the air that night, but this was not hanging evidence.
This season was a dry one. Several lakes reputed to harbor swans were found to be so low that even beaver houses were left dry. This suggests that in certain years swans attempting to nest on shallow waters may have their lakes vanish, or at least shrink until the nests are accessible to land enemies.
FIGURE 12. – Shallow lake in the Bechler district in
a dry season. Trumpeter swan nests
may suffer the same fate as this
beaver house.
Photograph taken July 24, 1931, in Yellowstone, by G.
M. Wright.
Wild Life Survey No. 2292
Winter status of the trumpeters was an open question because their movements after they were frozen out of the home lakes were not known. But during a cold spell early in 1932, 28 swans appeared on thermally warmed waters in the park. At the end of February the count totaled 41. This was good news, for, if the Yellowstone birds remain in or near the park in winter as well as summer, the hope of saving them is greatly increased.
The present indication is that the swans are at least hanging on. This permits of a little more time for intensive research to discover the critical factors during the periods of incubation, of raising the cygnets, and of absence from the breeding ponds in winter.
Many protective measures have been suggested, but it seems inadvisable to try much without better knowledge of the basic facts unless a tendency to further decrease becomes apparent. That would be an emergency justifying drastic action, such as removing all suspects from around the nesting lakes or raising a portion of the cygnets in semicaptivity where conditions could be definitely controlled. Measures in addition to the above which have been proposed are : Fencing coyote-proof lanes for swan travel between lakes, ranger detail to keep ravens cleared out during the incubation period, prohibition of entry to the breeding lakes by park visitors, enlistment of public support to wipe out the vandalism which is known to affect the swans when they are outside the park, and other suggestions.
The partial conclusions from investigations made to date are that whereas the trumpeter swan was decimated as the result of civilization's influence, and whereas the species may not be able to come back under ordinary park protection, it is desirable in consequence that there should be a program of careful study with a view to resorting to intensive management if further developments prove the necessity. This does not fail to recognize that low survival rate of cygnets may be normal for this species, inasmuch as the swan is long-lived and has relatively few natural enemies when full grown. But when the trumpeter is nearly extinct, it is important for as many cygnets as possible to survive, at least until such time as the breeding stock is restored to numerical safety. It is a case where special protection is amply justified as a temporary measure.
FIGURE 13. – Adult trumpeters and six cygnets (one hidden in
tules). The grown birds are
powerful and capable of protecting their
young in the water, but all are at a disadvantage
on land. (Note rubber
boat used by Survey in distance.)
Photograph taken June 20, 1930, at
Lamar River, Yellowstone. Wild Life Survey No. 880
FIGURE 14. – Two trumpeter swan cygnets from the same brood. Do
young of the gray phase
have a better chance of escaping enemies than
those of the white phase ?
Photograph taken June 12, 1931, at
Trumpeter Lake, Yellowstone by G. M. Wright.
Wild Life Survey No.
2268
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CONDITIONS CAUSED BY EARLY INFLUENCES OPERATING INDIRECTLY
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