Fall migration was well underway both months with some nights seeing the passage of hundreds of migrating birds moving southwards. Typically August is an under-reported month with birders less willing to brave the heat to look for the occasional rarity among the many nondescript juvenile birds. However, this year more birders seemed to realize that this is a great time of year for birding and we had reports of many unusual species. However, some common species (which were surely present) were not reported; in this category fall Golden Eagle, White-throated Swift and White-crowned Sparrow. September typically sees the peak of the fall migration; we had many reports but an over-concentration of them were for Sawhill and Walden Ponds. Altogether 156 bird species were seen in August and 166 species in September.

Both months provided some exciting finds. Union Reservoir was host to five species of tern: Arctic Tern (last seen in 2003), Common Tern (seen for the first time this year), Forster’s Tern, Least Tern (last seen in 1998) and Black Tern, which was also present at Walden Ponds. A juvenile Sabine’s Gull at Union Reservoir was a new sighting for the year. Shorebird migration was strong with most birders concentrating their efforts on Sawhill and Walden Ponds for which they were well rewarded. Sanderling (seen at Union Reservoir) were reported for the first time since 2004 as were Western Sandpiper and Pectoral Sandpiper. Other less usual shorebirds included Semipalmated Sandpiper, Stilt Sandpiper and Red-necked Phalarope. Sawhill and Walden Pond also had a good selection of herons with several Great and Snowy Egrets as well as the continuing presence of Green Herons. A White-faced Ibis seen at Sombrero Marsh was a less usual fall sighting.

Some birds are typically more likely to be seen during fall migration than in the spring. This was the case with Cassin’s Kingbird, Sage Thrasher and Townsend’s Warbler which were all new sightings for the year. Cassin’s Vireo which was seen for the first time since 2004 also seems to be a bird that is most likely to be seen in the fall. There were a few unusual warbler species; Nashville Warbler was new for the year, Palm Warbler was seen for the first time since 2004 and Canada Warbler was seen for the first time since 1996. Two unusual flycatchers were an Eastern Wood-Pewee and an Ash-throated Flycatcher.

It is much harder to evaluate the average date of leaving for most species than it is to find the average date of arrival. This is partly because birders rarely take note of the last time they see a species in a year and also because the occasional straggler may skew the dates. This is one reason why many reports of the same area can be very useful. It was possible to see the peak numbers for many species this year. For instance most of the Eastern Kingbirds had left Boulder County by the end of August with one lone straggler seen in September but Western Kingbirds were still around during the first week of September. However, the Cassin’s Kingbirds were seen later in September indicating that any kingbirds seen later in the month should be looked at carefully. Similarly, Bank Swallows and Cliff Swallows seem to have left the county by late August; Tree Swallow and Northern Rough-winged Swallow were seen the first week of September and Violet-green Swallow were here until at least the third week of September. Typically, Barn Swallow is the last swallow to leave Boulder County with early October sightings not being unusual. TOP

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Mammals, Reptiles and Amphibians