Birders, Dave Martin wrote (in part):
> Alan Wormington and I experienced this frustrating phenomena in Essex > County on Saturday morning. He was watching hawk migration at his Seacliff > site. At the same time, I was about 10 km inland at a station near > Blytheswood on Hwy 77. His Broad-wing total for the morning was just over > 400 birds and mine was 61 birds. Yet, as you know from reading the hawk > reports for that day, Holiday Beach recorded nearly 20,000 and Erie > Metropark recorded 130,000 birds [albeit both of these sites counted all > day whereas we only counted from 0900 to 1200]. However, in each half hour > of our count, the number of hawks diminished. Even if we hadn't planned to > stop at noon we would have anyway, as the number of hawks had diminished to > the point where we would have given up. This leaves many questions of > course. Where had the birds started that day? Were the "TUVs" already so > strong early in the morning that they rose high enough not to be seen when > they passed over us if they did? Why do they descend low enough to be seen > at Holiday Beach and Erie Metropark? Is there some other unknown flight > path through Essex County? I counted hawks at Holiday Beach for 25 years, and as a Michigan resident I have been to Lake Erie Metropark many times. First, I can tell you that many Broad-wings at Lake Erie Metropark are still quite high. Also, there are typically many flight lines there, with stronger northwest winds blowing birds down toward the Pte. Mouillee area. At Holiday Beach, we have been aware that some Broad-wings pass to our north, far enough inland to be invisible (usually 3-10+ km). Most birds at Holiday Beach (especially after noon) are also painfully high up, sometimes barely visible in 10x binoculars. Also, we do have birds that get blown out over Lake Erie to the south, sometimes surprisingly far. In this latter case, the birds become extremely difficult to see as they are not presenting an overhead silhouette, but a side-on view. Combined with the fact that these birds might be 2000-3000 feet up and 1/2 mile away, plus often directly into the sun, it could be easy to miss a lot of them. The flight line to Pte. Mouillee seems likely to be partly from these offshore birds. So, birds coming down an ever-narrowing peninsula to the southwest seems to me to be a good explanation why Holiday Beach gets more birds than Hawk Cliff (sometimes). Also, the geographic situation at the mouth of the Detroit River, along with the bird's more purposeful flight, might tend to make the birds group up even more, and as they're crossing they don't usually zigzag around like they do at Holiday Beach, making it more straightforward to count them. Just my ideas. I could be totally wrong! Detailed radar images on such peak days could tell us a lot. Allen Chartier [EMAIL PROTECTED] 1442 West River Park Drive Inkster, MI 48141 Website: http://www.amazilia.net Michigan HummerNet: http://www.amazilia.net/MIHummerNet/index.htm
