Notes about your surroundings.

Rare Birds--Orange County bird enthusiasts are familiar with the great blue heron, a majestic blue-gray bird that--standing almost four feet high--is a conspicuous sight along the Santa Ana River and in local estuaries.

But there is also such a thing as a little blue heron that is seen in the Southeastern United States but is rarely found this far north on the Pacific coast. Although a few are seen regularly in San Diego, sightings are made in Orange County only every three or four years.

One little blue heron, first spotted in January, has been making a temporary home in Upper Newport Bay. It is an immature bird whose white plumage makes it difficult to distinguish from the snowy egret, but when last seen on March 11, it was starting to molt and its darker adult plumage was beginning to sprout.

Another locally rare bird is the glaucous gull, which is rarely seen this far south. There are only six spottings of the gull in Orange County, according to birder Doug Willick, who tracks rare bird sightings in this area.

Jim Pike spotted one of the birds March 14 along the Santa Ana River in Anaheim, picking it out from among a group of thousands of California and ring-billed gulls that travel along the river each day between the sea and inland landfills.

Other recent rare sightings:

* Merlin, Santa Ana River, March 17. Rarely seen locally this late in the season.

* Williamson’s sapsucker, Anaheim Hills, March 2 and 3. Usually found in coniferous forests at high elevations. Third Orange County record.

* Harris’ sparrow, Irvine Regional Park, early January (most recent sighting, March 2). Usually spends winters in Texas and Oklahoma.

Migration--Swallows are among the first spring migrants to arrive in the county, with several common species usually spotted in late February. One of the rarer species, the bank swallow, usually doesn’t arrive until April, if at all.

So far, however, two bank swallows have already been sighted in the county--one at Irvine Park on Feb. 28 and another at Yorba Regional Park on March 3. “Both of those are extremely early,” Willick said.

One locally rare swallow that hasn’t been spotted yet is the purple martin, which once bred in large numbers in the county but has been displaced by nest competition from the more aggressive European starling, a non-native bird. Both birds nest in cavities, such as those found in dead trees.

“Purple martins are pretty timid, and they couldn’t compete,” Willick said. “Their numbers on the West Coast are fairly decimated.”

Land birds that are beginning to migrate into the county: warbling vireo, Wilson’s warbler, hooded oriole and northern oriole. Another is a bird still known in guide books as the western flycatcher, although its name was recently changed to Pacific slope flycatcher.

Earth Day Countdown--The Orange County Earth Day 1990 Coalition has scheduled a series of Saturday activities leading up to the observance of Earth Day on April 22. This Saturday, volunteers will meet at 9 a.m. at University High School in Irvine, Campus Drive and Culver Street, to pick up aluminum cans collected by Irvine residents and to plant native wildflowers at Mason Regional Park in Irvine.