For the past three seasons (2017, 2018, 2019), Purple Martins have formed a premigratory roost in the trees of the US Army Corps Lock & Dam #4 facility in Natrona, PA. This video was taken in 2018. The roost has grown to 5000 – 7000 martins, which gather in the evening into large swirling formations and eventually land in several large trees on the Corps grounds. The roost forms all through the month of August with peak numbers occurring in mid-august. The martins begin gathering about an hour before dark, streaming in from all directions, landing on wires and and swirling in large formations several hundred feet above the Allegheny River, eventually landing in the trees in spectacular fashion just before dark (watch video above). There is a 20 pair Purple Martin colony on the grounds. This colony was established by Ken Kostka in 2005 with one breeding pair that was displaced from the Saxon Golf Course colony near Saxonburg, PA as part of a project intended to establish new breeding sites. There are several other articles about the Lock 4 colony and the displacement project on this website. I hope to publish more information and videos here about the roost in the future as time and energy permit.
If you want to view the site with GoogleEarth, the address is:
1 River Rd., Natrona, PA 15065
There are also many articles with photos about the Lock 4 Purple Martin colony on this website.
Additional video of roost and Lock 4 facility:
video of roost (swirling formations) in August 24,2017:
video of martins bustling in the trees:
Below is GoogleEarth Photo of the Lock 4 facility, 1 River Rd., Natrona, PA on the Allegheny River in northeast Allegheny County. The red lines converge in the lawn area containing the martin housing and the roosting trees. This is a restricted U.S. Army Corps of Engineers Facility, not open to the public. Viewing must be done from outside the fencing. The large parking lot to the east is a good vantage point. This is a large private parking lot that is usually pretty empty but I’d stay with my car. The other option is a small parklet just downstream of the Lock facility. This parklet can only be accessed by way of a dead end alley. The entrance to this alley is 0.36 south of the Lock facility off River Rd. The parklet viewing area is better for watching the large swirling formations that form above the river, but the parking lot viewing area is better for watching the martins as they come down into the trees, also a spectacular sight.