I'd been meaning to post on this some time ago, but never got to it, for one reason or another. It is no surprise to most birders familiar with Orange County birds that the Lesser Nighthawk is a regular summer resident in the county, even if very localized and in small numbers. It is also known to be an irregular, scarce migrant through the county (most occurring in fall). Several years ago it was brought to my attention (by Steve Alter) that above average concentrations (per Orange County standards) of Lesser Nighthawks could be seen, at least in spring, at Peters Canyon Regional Park. For example, "a few dozen" were seen here in spring 2002; 21 here on April 15, 2006; 30 on Apr. 23, 2007 (reports by Steve and Marian Alter).
Then this year Steve informed me that they had by far the most they've ever encountered at Peters Canyon (when they made a rough estimate of about 80-100 on May 11 and 12). These seemed to be unprecedented numbers for Orange County, so I finally got down there on the evening of May 15 to take a look. It took awhile for the first bird to finally appear, but within 10 minutes I had a very hard time trying to estimate how many were present; made a wild guess of somewhere in the vicinity of 75 (and I wouldn't have been very surprised if the numbers were indeed higher). After their initial appearance over the upland areas surrounding Peters Canyon Lake, the nighthawks were concentrating their feeding low over the lake, and could be seen from one end to the other. Wondering if this is just a spring phenomenon, I made another visit just this past Tuesday (May 29) and only estimated about 20 to 25 (when the first didn't appear until 8:06pm). I'm not really sure what to make of this, whether this represents an unusually healthy breeding population in the nearby foothills and upper Santiago Creek wash, or if concentrations of migrants occasionally augment the local breeding population in spring. Peters Canyon Lake does appear to be a rich foraging area for aerial insects, as there could have been as many as a few hundred swallows feeding actively over the lake at and just before dusk, and a good number of bats began appearing before the sky became too dark to really see much.
For those that might be interested in seeing Lesser Nighthawks here (though the larger numbers seem to have certainly declined), the dirt parking lot at the north end of Peters Canyon Regional Park (off Canyon View Avenue, just east of Jamboree Road, in Orange) unfortunately is usually locked at 7:30pm on weekend evenings (such as it was when I tried to make a nighthawk count last Saturday evening, the 26th). On weeknights, however, it seems the rangers don't close the gates as early (I've left as late as almost 8:30, and the gates were still open). There is a sign that says the parking lot closes at 7:30 at this time of year, but the trails and park itself remains open. One could park in the residential areas northwest of the lake parking lot, but there is no parking allowed directly across from the parking lot, or along Canyon View Ave. (so a walk would be involved of a good 1/4 mile or more). In any event, I was quite amazed by the number of Lesser Nighthawks present (especially during the early to mid May visits). The previous high count reported in Orange County was 43 along San Juan Creek (just inland from San Juan Capistrano) on July 13, 1989.
A calling Least Bittern was heard at dusk on the May 15 visit, but not on the 29th.