Insight: First push of Broad-wings

A migrating Broad-winged Hawk comes low over the parking lot at the Black Swamp Bird Observatory in northwest Ohio, late in the day on April 15, 2012. Photo by Kenn Kaufman.

April 15: Last week I had predicted that we'd get a good hawk flight today, "including the first big push of Broad-winged Hawks for the year."  That was on another blog where I try to make predictions for the migration in n.w. Ohio; the link to it is here.

Of course, after I make these predictions, then I'm sweating it, hoping that they'll prove to be accurate.  Today, through the middle of the day, I was beginning to doubt that it would happen. 

Here in n.w. Ohio, good spring hawk flights happen mainly on warmer days with southwest winds.  The hawks are moving north on a broad front, but the southwest winds shift them toward Lake Erie; then they cut back to the west-northwest, paralleling the shoreline, until they can turn the corner at the western end of the lake and continue north into Michigan.  Today we had good southwest winds, but after some stormy weather overnight, nothing seemed to be happening with the hawks during the morning. 

Shortly after noon I went to the hawkwatch tower at Magee and spent half an hour.  I did see one Broad-winged Hawk and a few Sharp-shinned Hawks, but not much else, so I went elsewhere.  Sometime after 1:30, Ethan Kistler called me from the hawkwatch tower, to tell me that things were picking up.  I went back there to watch.  Ethan and I watched from the tower for a while, then went to Maumee Bay State Park, then to the west edge of Ottawa NWR, then after 6 p.m. we were back at Black Swamp Bird Observatory; everywhere we went for the whole afternoon, we saw Broad-wings and other hawks migrating.  It was definitely a major movement.

I think a couple of things contributed to the quality of today's flight:
1.  We had had northerly winds most of the time for more than a week before this.  Broad-winged Hawks are affected by wind direction, so they probably had been dammed up somewhere to the south of us, just waiting for a good day to move.
2.  Winds of about 20 mph by late morning were good for getting the hawks moving.  Later in the afternoon the winds were stronger, gusting to over 30 mph, and I think this was influencing the birds to fly low so that they were very easy to see.  On a calmer day, they might have been flying much higher.  Indeed, at Maumee Bay, the Sharp-shinned Hawks were flying only a foot or two above the ground or above the water in open spots. 

Insight: Too much of a good wind

March 7: Here along the Lake Erie shoreline in n.w. Ohio, we get good hawk flights in spring mainly on days with southwest winds.  With any kind of south winds, or with warm calm weather with good thermals, the hawks will be moving on a broad front, but they won't concentrate anywhere.  Southwest winds push the birds up toward the lake shore, and they then correct and move west-northwest paralleling the shore, aiming for the west end of the lake where they can turn and go north into Michigan.

Today we had southwest winds but they were evidently too strong for a lot of the migrants.  With winds of 30 mph, and stronger gusts, there were probably no thermals rising anywhere, and the smaller hawks that were flying seemed to be having a tough time of it.  I spent a while at midday watching from the observation platform at the corner of Krause and Stange Roads (west side of Ottawa NWR) and saw very little flying.  (Well -- lots of debris, leaves, etc., flying on the breeze, but not many birds.)  Continuing west to Maumee Bay State Park, I counted 220 Turkey Vultures in an hour and a half, but only small numbers of other hawks (just a few Red-shouldered and Red-tailed hawks, Northern Harriers, and a couple of American Kestrels).  Even the Turkey Vultures were rocking in the wind, and the other birds were having a tough time.  I'm inclined to think that ideal conditions would have lighter winds, perhaps 15 to 20 mph from the southwest.