Explaining Chukar Population Fluctuations

Idaho chukars must endure heavy snows
By Andy Ogden
For the Idaho Press-Tribune
Andy Ogden is a Wildlife Habitat Biologist for Idaho Department of Fish and Game — Southwest Region.

Idaho’s chukar partridge (Alectoris chukar) is native to a wide swath of southern Europe, Asia Minor, Northern India and China. Several chukar subspecies occupy these native ranges, each with its own set of distinctive behavioral traits. Interestingly enough, the subspecies that was transplanted into Idaho and other western states years ago never had to cope with extended periods of deep snow in its native homeland. In these areas, the birds had the option of simply descending to lower elevations to escape heavy snow. In northern India for example, it is still possible for chukars to move from the slopes of the Himalayas all the way down to tropical rain forests!

Unfortunately, Idaho’s chukars don’t have that luxury, and southern Idaho populations have experienced their share of large winter die-offs. During the 1992-93 winter, the Brownlee area experienced unusually heavy snow falls coupled with little wind to expose ridge lines. This weather pattern held for over a month, and chukars paid the price: crowded into riparian areas along streams and reservoirs, chukars died by the dozens. Many were so weak that they were unable to fly across reservoirs, and proved to be easy pickings for predators. Birds in this condition were onehalf their normal weight, with breast muscle reduced so much in size that their keel bones protruded noticeably.

Experience shows that chukar populations can recover entirely from a tough winter within two nesting seasons if conditions are good and reproduction is normal. For example, in the fall prior to the tough winter of 1992-93, biologists counted 78 birds rebounded to 88 birds/square mile per square mile in the Brownlee area. (a number similar to the fall of 1992) A record-low 18 birds/square mile was after just two nesting seasons documented the next fall. Numbers this past winter, snow depths were fairly extreme on chukar winter ranges, though probably not deep enough to mimic population crashes of the past when heavy snows were accompanied by cold temperatures which added additional physiological stress. This is fortunate because late fall 2007 chukar populations were already very low due to extremely poor summer reproduction. Some chukar populations (including Lucky Peak, Arrowrock and Garden Valley) likely declined even further this winter due to snow levels, while other populations where snow levels were less extreme (Brownlee, Hell’s Canyon and Owyhee, for example) probably fared better.

For maximum winter survival, chukars require significant fall “green up” of perennial bluegrasses coupled with germination of annual cheatgrass seed. These high value food sources allow chukars to actually gain weight during the winter so that nesting hens have significant fat reserves when spring nesting season rolls around. It is believed that the vitamin A found in this green vegetation is vital for triggering the reproductive instincts of game birds, including chukars. For example, in the very dry deserts of California and Nevada, upland birds won’t even attempt to nest without sufficient green up of desert vegetation stimulated by adequate winter rainfall.
In falls without significant green up, chukars survive on the seed heads of grasses and the seeds of perennial forbs like stonecrop and those of annual weeds like thistle. These food sources can maintain chukars through the winter, but to gain body fat they really need the added nutrients found in green grass. Fortunately, Idaho experienced good fall green up in 2007, so chukars should be in good shape for the 2008 nesting season.

That brings us to the subject of the spring nesting season. Ideal chukar production weather plays out something like this: a wet spring with lots of rain (but no snow) for maximum growth of leafy green vegetation needed by adult birds and the production of lots of bugs that chicks require early in life. This would be followed by dry weather in early June when the chicks are hatching to increase their survival during the critical first few days of life. It might surprise you how rarely this relatively simple scenario occurs.

It is too early to know how spring production will fare and thus difficult to predict the fall chukar hunting picture given that last fall’s population levels were the result of reproductive failures, not winter weather. Because chukars are short-lived birds (a three year-old bird is both old and very rare) it is critical that a good nesting effort occur in 2008. A high proportion of Idaho’s chukars are already two years (or more) old. If we experience a poor nesting effort this spring, most of these adult birds won’t see another nesting season; if that happens, it may take four or more years to recover southern Idaho chukar populations.

Even with above normal nest success this spring, it will probably still take two nesting seasons to get out of the hole we’re in right now. So pin your fall chukar hunting hopes on a wet (but not too wet) spring.