Three routes have been monitored consistently in the years since 1989-90. The Rabbit Mountain and South County routes were skipped in 1992-93, but there is data for all the other years. The Boulder Reservoir route has been monitored every year. In the early years, Ferruginous Hawks (FH) and Red-tailed Hawks (RT) were about equally common on the Rabbit Mountain and South County routes. Even in those years, the FH were much less common on the Boulder Reservoir route. Beginning in 1995, the RT started to become more common, while the sightings of FH plummeted and have slowly become rarer ever since. Rough-legged Hawks were comparatively scarce even in the years near 1990, and they have become even rarer recently.
On the Rabbit Mountain route, Ferruginous Hawks and Red-tailed Hawks (RT) were almost equally common initially, but the RT have increased dramatically since 1995.
Heavy development along the South County route has kept the density of all three species much lower than on the other routes over the entire period. It is particularly notable that sightings of RT have increased only slightly, in contrast with the large increase seen on the other routes.
On the Boulder Reservoir route, RT have been the predominant species over the entire 1990-2008 period, increasing much less than on the Rabbit Mountain route. The RT density is currently comparable on the two routes. FH observations have declined less near Boulder Reservoir than in the Rabbit Mountain area.
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