Cattle Egret invasion?

Cattle Egrets are small white egrets that expanded to the western hemisphere from their natural African range in the early part of last century. The first record for Ontario was in 1956, and it gradually became a more common visitor, even nesting on occasion. Numbers seem to have peaked in the 1970s, although they are seen regularly in small numbers most years.

The first record for the Rondeau checklist area was on April 19, 1970, when two birds were observed. There have been several dozen records since that time, although 1973 was the year when they were most frequently seen and in the greatest numbers. The first record for that year were four birds on April 28. As many as 12-20 birds were seen regularly in May, and the last report for the year was of five birds on September 24.

Since that era, birds have been seen periodically, but usually only one or two at a time. The latest they have been recorded in the park checklist area in any year was a single bird on November 21, 1987. (I did have 4 birds at the Tilbury Sewage Lagoons, just inside Essex County, on Nov 1, 2014.)

The fall of 2016 has seen a minor influx of these birds. They have been reported in the last few weeks in various places across southern Ontario.

Most recently, they have shown up again in the Rondeau area. A birder/hunter reported one a few days ago flying over his blind along Rondeau Bay. In the last couple of days, two were seen regularly at the Blenheim Sewage Lagoons.

This morning, I went to the lagoons as they were reported there late yesterday afternoon. I arrived and noted two birds towards the far end of the main path between the ponds. Approaching them cautiously, I realized they were headed my way, so I stopped and waited for them to get even closer.

From time to time, I looked back towards the lagoon entrance to see if anyone else was coming along. Two birders appeared...it was Steve Charbonneau and his son Aaron....and then much to my surprise, two more Cattle Egrets appeared between us. At this point, I was somewhat 'trapped' by two pairs of the egrets....I didn't want to move for fear of spooking them. I did see a way out, however, by moving to a side path, waiting for the second pair to come by.

And come by they did, although I think when they got by the shrubby willows I was using to hide behind, they realized I wasn't part of the landscape, and took to flight. They were almost too close to get in the field of view....this next image has not been cropped even a bit, and I barely got them totally in (actually, the closest bird has one foot outside the image).

They didn't go too far, but joined the first pair of birds farther down the path.

They circled around and resumed feeding on the numerous grasshoppers in the recently mowed grassy area.

While four birds does not constitute an invasion in the true sense, in combination with the reports from several other areas across southern Ontario, just how many are out there? Are these two pair covering lots of territory and the reason for those many reports, or are there several other pairs out there?