Thursday, September 24, 2015

Raptors on your Radar?

Duluth Area Map
I'm sure many of you will have stumbled upon the concept of birders and ornithologists checking out the night's NEXRAD Radar readings to look for migrant land birds flying during the night. What many don't seem to have cottoned on to is that you can do exactly the same thing with raptors. For some basics on using radar to observe bird migration check out eBird (here). 

Tom Carrolan, author of the irreverent Hawks Aloft blog (read it here), from Derby Hill is a big proponent of studying hawk flights on radar. He sent me an email this week with some cool images and video from the first big flight at Hawk Ridge on September 12th. Above I have attached an image of Duluth so that you can see where the lake etc is. Hawk Ridge Bird Observatory is a couple of miles north of Duluth, right along the lake shore.

From here I'll let Tom explain:

Radar capture of Hawk Ridge Flight (the thin blue line)
"Above is a still image showing the typical Hawk Ridge flight line affected by the lake line… initially it’s on rails at the shore (indicated by the thin blue line of raptors). As the day goes along you can observe the raptor flight drifts inland (west). From the day's hawkcount report conditions were described as southwest to east, however, they were certainly northwest inland as indicated by the still image and radar loop, which would indicate the SW-E readings at the lake were caused by a lake breeze.

This link is for a two-hour sample, showing the flight. Note birds at the northeast end of the loop first, then look towards the hawkwatch

The radar shows exactly what was observed on the ground. From the report: "Broad-wings started strong during morning lift off, but the kettles drifted off to our west with the light easterly breeze, two more dark Swainson's were spotted, the fifth day in a row” (you can read the days report on BirdHawk here)."

As far as I'm concerned it's really cool to be able to see and capture the flight of birds during a day like this. It allows you to see both how a large flight of raptors looks on radar but also to get an idea of what you were missing by being stuck at one site if the flight lines of the birds move. Another thing for radar fans to mess around with. 

Out of interest, here's the radar loop from their 17 thousand bird day on the 19th of September (click link).

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