This morning we saw over 10,000 Yellow-rumped Warbler fly past the Sanibel Lighthouse in two hours. Wow!
The warblers launched off the lighthouse tip, flying into a strong wind, headed for the distant shore.
They fly with strong rapid wingbeats in a burst, then sail for a millisecond with their wings tucked and look like little bullets.
It all started out innocently enough. I said to Don,
"Let's take Phoebe to the lighthouse, I need photos of the lighthouse to go with some bird images I took there yesteday".
We arrived and strolled down the center path, puppy and hubby not happy with my slow "I'm-looking-for-photo-ops "pace. On the corner, birds were huddled in the ditch, hiding from the cold, strong, north wind. I saw this Anhinga drying its wings and waited for the moment the blowing grasses parted and framed its face, to get my composition.
We to the beach to get the classic postcard photo of the Sanibel Lighthouse and began to notice Turkey Vultures milling overhead. They may have been getting some lift off warm air rising from the parking lot, since it was too cold and windy for good thermals. They looked like bats coming out of a belfry.
Suddenly we were hearing and seeing lots of Yellow-rumped Warblers. They were launching themselves in groups, headed right into the wind, out over the waves. At 9:08 am we decided to start counting them. We continually took sample counts of the number of birds flying by in a minute. Our low count per minute was 75; our high count was 125 and most counts were this number. They were surprisingly constant. We chose a number of 110 birds per minute as a conservative estimate and multiplied that by the number of minutes we watched. We also continued to sample the number of birds per minute to be sure the pace had stayed the same.
From 9:08 am to 10:28 am the pace of birds was constant and totalled 8,800 warblers. From then to when we stopped counting, 11:08 am, the pace slowed to 50 birds per minute and totalled 2,000 birds. In all we had 10,800 Yellow-rumped Warblers in 2 hours!
How many warblers actually passed over the lighthouse on their way to the mainland that morning? We can only guess. They could have easily started an hour earlier bringing the total to 17,400; and continued later making totals close to 20,000.
We noticed birds flying at various heights. In the first hour, many were about 50 ft. high and easy to see, but as we looked higher we saw many more 150 ft. high. During the second hour, when we thought things had slowed down a bit, we suddenly noticed hundreds of birds flying at the limit of our binoculars. They looked like little snowflakes, totally invisible to the naked eye. We had not thought to look this high earlier, and may have missed them, making our totals much higher.
Here are some other thoughts and observations we had. There was a strong north wind which they had to struggle against as they crossed east to the mainland. Why would they pick this time to cross? We conjecture that these birds chose to move because the north winds helped them come down all the barrier islands, which are oriented north/south, and this left them on the last island, Sanibel, which is oriented east/west. At this point, they had to head to the mainland by the shortest route which meant slightly against the wind.
We wondered if any birds were just circling back over the water and returning to the island and thus being repeatedly counted by us. We checked this by following individual birds and groups of birds as long as we could. They always kept going until they were out of sight. We also looked for any birds coming back onto the island. There were none. Thus, we felt sure we were not double counting.
We wondered why the stream of birds was so constant. Why were we not seeing 500 warblers all at once and then none for a while. The pace, as we continually checked it, was amazingly constant. We think this means that the warblers were fairly evenly distributed over the barrier islands before they started flying and that most started flying at about the same time, thus creating a steady flow. This may be due to their feeding habits, insects and berries, where large flocks could not find enough to eat. There are still questions here to be answered.
Also, where were are the birds going? And why? We do not know. We also do not know if anyone has reported a similar winter movement of Yellow-rumped Warblers. The reference, Birds of North America, makes no mention of movements like this.
Other birds we saw while out there were about 30 Cedar Waxwings heading out over the water but circling back. This was also the case with a flock of 200–300 American Robins. At one point we saw 200–300 Tree Swallows take off from the island about 1–2 feet over the water, going to the mainland.
At one point I decided to watch just one Yellow-rumped Warbler until it disappeared out of my sight. It got blown around then joined others. I realized it could see hundreds of other yellow-rumps up there where it was. What a strong urge compelled it to fly with its like kind, the flock instinct and migration urge functioning like a big magnet to pull these thousands of Yellow-rumps back to the mainland. It was our very own "Winged Migration" moment.
Bird photos © Lillian Stokes, 2007