From late August through the end of October I am trapping and banding hawks, falcons, and (hopefully) eagles as they migrate southward for the winter. Situated at the southern edge of the Boise Ridge at 6525 feet elevation, perched within viewing distance of Boise, Idaho lies the Idaho Bird Observatory’s (IBO)Boise Peak hawk migration trapping station.
Migrating raptors are concentrated and thus easier to trap here because of the landscape features. Raptors use thermal uplift generated from the mountain slopes, expending as little energy as possible as they move southward. The Boise front is also the southernmost extension of the Idaho mountains, ending abruptly at the Snake River Plain.
But how do I capture these hawks? Well here in lies the most intriguing, exciting, and yes, addicting part. For those of you who hunt, fish, or enjoy any type of tireless and time-consuming effort with sometimes no payoff, you will understand the allure of hawk-trapping. Lure birds (House Sparrows, Ring-necked Doves, and your standard pigeon), all of which are invasive and non-native and therefore not protected by the Federal Migratory Bird Act are used to lure in hawks as they migrate past Boise Peak.
Each lure bird wears a protective harness which is attached to lines that run back to the blind where I sit. These lines are pulled causing the lure birds to pop into the air and flap their wings. The largest lure bird, the pigeon is “popped” every 90 seconds, so that any passing raptor will be drawn into the trapping station.
Depending on the size of the raptor, I will then use the smaller dove or sparrow to lure it in. Three types of nets, the Dho-gaza (DG), bow-net, and mist-net are used to capture the raptor. The mist-net and DG which surround the lures are virtually invisible to the raptor which will hopefully fly into and become tangled.
The bow-net on the other hand requires the raptor to land on the lure bird. A trigger is then pulled and the spring loaded bow-net closes on top of the bird.
After being captured, hawks are banded with uniquely number federally-issued bands, and data is gathered on body size, age, and sex.
At the end of the season, information on the birds and the band numbers associated with them are reported to the USGS Bird Banding Laboratory (BBL). The hope is that birds will be recaptured or recovered, giving us an idea of where they go and how long they live. For those of you that ever discover a banded carcass, please report that band to the BBL.
On August 31st 2012, after two full days of set up entailing running lines, placing dho Ghaza poles, fixing DG’s, adjusting lines, pruning the surrounding vegetation, cleaning the trailer of hopefully Hanta virus-free mouse droppings the fall migration hawk trapping season was ready for action. Although it was already 6:00 pm I was itching to start trapping. Shortly after I started I captured a Hatch Year (HY, that is a bird that hatched this spring/summer) Sharp-shinned Hawk The following day I was pleasantly surprised to trap and band 17 birds, an fairly high number for this early in the season.
Early in the season early we primarily capture hatch year accipiters, our sharpies and Coopers Hawks. Migration phenology follows a fairly distinct pattern. As mentioned, hatch years birds pass through first, followed by adults.
It is always exciting to see the first adult accipiter as they are strikingly different in appearance with their orange to brick red eyes, slate gray upper parts, and rufous barred underpants.
This late summer and fall forest fires are pervasive. Smoke has on many days obscured my view of Boise and the surrounding landscape.
It has led me to wonder how this affects raptor movements and even survival. I can only hope it doesn’t affect my numbers too much!