Another question of possible interest is the distribution of the less common raptors: Bald Eagles, Golden Eagles, and Northern Harriers. Are they significantly more common onone of the routes than the others? The straightforward answer is that the differences aren't large.

We examine first the Bald Eagles. One might expect that they would be more common on the Rabbit Mt. and Boulder Reservoir routes, because the routes pass close to two large reservoirs—Lagerman Reservoir and Boulder Reservoir. This expectation is borne out by the data. It appears that 1989-90 was an anomalous season, in that many more Bald Eagles were recorded on the Rabbit Mt. route than in any other year (0.76/km), while none were seen at all on the Boulder Reservoir route. This anomaly is not apparent when all the routes are summed; a possible explanation is that the Boulder Reservoir Bald Eagles were mistakenly lumped with the Rabbit Mt. observations.

Golden Eagles have occurred with similar frequency on all three routes. Once again there is one year in which the Rabbit Mt. value is conspicuously large, 0.232/km in 2003-04. That value is approximately double the two peaks in 1993-94 and 2001-02. There is nothing unusual about the values for the other two routes in that year.

Northern Harriers are less common than eagles on all three routes (note the different scale on the graph). They are extremely scarce in the South County, even in tne earlies years in the chart. This difference can probably be attributed to limited suitable habitat and to increasing development. On average, the frequency on the other two routes is similar and quite variable.

Return to the Wintering Raptor summary page

Page comparing pairs of species

Page comparing abundance of 3 common hawks on three survey routes