POPULATION
Ruffed Grouse normally have a short life span. From a brood of 10 or 12 hatched in late May or early June, usually 5 or 6 will have died by mid-August. Among those living to disperse during the fall shuffle, about 45% will have been lost by late fall and early winter. Another 10% die over winter and during early spring, so that only about 45% of the young grouse alive in mid-September live to their first breeding season. In subsequent years a given cohort (a season’s crop of young birds ) continues to shrink by about 55 to 60% per year. So from 1000 chicks hatched in late spring, about 400 normally survive to early autumn, 180 survive to the following nesting season, 80 are alive a year later, 36 live to breed a 3rd time, 16 may breed a 4th time. One out of 2200 chicks hatched may live as long as 8 years.
Most Ruffed Grouse die a violent death to provide a meal for one of a number of meat-eating predators, for in the natural scheme of things, Ruffed Grouse are one of the first links in a complex food chain. Some also die from disease and parasites, or from exposure to severe weather, or accidentally by hitting trees or branches while in a panic flight after being frightened.
Across the major portion of the Ruffed Grouse range, the winged predators or raptors are most efficient at taking these birds. Although the goshawk is certainly the most efficient of all grouse predators, the horned owl probably kills more grouse annually than any other predator. This is due to the cosmopolitan distribution of these owls and the likelihood that any woodland capable of supporting grouse will have resident horned owls, or at least be regularly visited by them. Yet, where cover is adequate, grouse can find security and maintain their abundance even when goshawks and horned owls live and nest nearby.
Conditions are seldom static in the world of the Ruffed Grouse and their numbers fluctuate from year to year, and from decade to decade. Across most of their range in the northern states, Canada and Alaska, Ruffed Grouse numbers have risen and fallen in a somewhat predictable pattern for most of this century, in what is often called a “10-year cycle”. In the Lake States, for example, periods of abundance usually coincide with years ending in 0, 1 or 2, and the bottom of the depression in years ending with 5 or 6. This is not invariable, but a general, regional trend. These “cycles” sweep across the continent more or less as a wave, beginning in the far Northwest and Northeast, and progressing southward and southeastward.
The factors responsible for these periodic fluctuations remain poorly understood, and appear to involve a number of different factors interacting with one another in different ways at different times. The one factor which does not appear to be important is hunting during the period of fall dispersal.
The primary causes for the short-term fluctuations in Ruffed Grouse abundance appear to be related to weather trends and variations in the quantity and quality of food resources. These are interrelated to a large degree. Superimposed upon these two basic factors is that of predation – as predators take advantage of grouse placed in jeopardy by unfavorable weather conditions or inadequate food resources. A favorable combination of weather factors and food resources may allow these grouse to survive the winter nearly immune to predation. These combinations of factors also affect annual production. If grouse spend the winter feeding on poor quality foodstuffs, or have to use an excessive amount of energy to keep warm, hens may not have sufficient reserves to produce a clutch of viable eggs, or vigorous, healthy chicks in the spring. Across most of their range, the most productive and most abundant Ruffed Grouse populations are those living where they spend most of the winter burrowed into 10 inches or more of soft, powdery snow, and emerge for only a few minutes once or twice a day to take a meal of the male flower buds of the aspens. Our Ruffed Grouse can be considered snow lovers or “Chionophiles.” Ruffed Grouse tend to be less numerous and less productive if they live in regions where they cannot burrow in snow and feed on aspen (poplar).
There also seems to be a poorly understood relationship between the color-phase of a Ruffed Grouse and its ability to survive severe wintering conditions, and its vulnerability to predation.
Longer term changes in Ruffed Grouse abundance reflect how we have treated our woodlands and forests. There is also reason to suspect that much of the severity of the “10-year cycle” is largely a result of how we have treated forested lands. These birds depend upon the food and cover resources produced by a group of short-lived trees and shrubs growing in full sunlight which develop following the severe disturbance of forests. In earlier times, fire and windstorm were the ecological agents periodically renewing forests and creating satisfactory habitat for Ruffed Grouse and many other species of forest wildlife. Ruffed Grouse should be considered a “fire-dependent” species in the natural scheme of things.
Our current reluctance to cut forests, even under strict management plans and the suppression of fire to protect growing forests, have upset this natural sequence of events. In the early part of this century, farm abandonment and the recovery of forests from unregulated logging and fires produced habitats which probably resulted in the greatest abundance of grouse in recent times in most of Canada & northern United States. But as forests mature under protection from fire and cutting, they lose the habitat qualities Ruffed Grouse require. In many regions, Ruffed Grouse numbers have declined as forests have become more extensive and older.
Ruffed Grouse abundance can often be readily restored by proper harvest management of forested lands, or through the judicious use of prescribed fire that is ongoing in northwestern Ontario.
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