At sea the black-throated blue warbler has been observed on October 27, 1921, 12 hours run out from Port-au-Prince, Haiti, toward New York; and on March 29, 1918, in the Gulf of Mexico, 125 miles from Sabine Pass, La.
Destruction at lighthouses.—Lighthouses with fixed white lights have caused considerable destruction of bird life during migration and the black-throated blue warbler seems to have been especially lured to those in southern Florida. Records were received from several of these lighthouses over a period of 5 or 6 years. Those from Sombrero Key are most detailed and give an interesting picture of migration at that point, since they include date, weather conditions, number of birds that struck, number killed, and hours during which the birds struck the light.
Comparatively fewer birds struck the light in spring than in fall. The spring dates are from March 9 to May 29; but in 4 years birds are reported to have struck the light only on 24 nights and 4 individuals is the greatest number reported.
In the fall, the records extend from September 3 to December 5, the heaviest nights being from the middle of September to late October. In two different years birds struck the light on 19 nights in two months. The greatest number in one night was 400 with 56 killed. In one of those years 1146 birds struck the light; of these 193 were killed. It was not only on stormy nights that the birds were attracted, as 130 struck and 15 were killed on a night described as calm and dark. Sometimes they kept striking all night, but on others the flight seems to have been concentrated, as when 300 birds struck in 31⁄2 hours. On a few occasions the mortality was as high as one-third of the birds that struck.
On the night of January 26, 1886, two birds struck the light. These were either wintering birds or extremely early migrants.
Egg dates.—Massachusetts: 6 records, May 28 to July 5; 3 records, June 2 to 8.
New Hampshire: 17 records, June 3 to 22; 9 records, June 10 to 15.
New York: 51 records, May 29 to June 20; 37 records, June 3 to 12, indicating the height of the season.
Pennsylvania: 57 records, May 25 to June 26; 32 records, May 30 to June 6.
North Carolina: 10 records, May 5 to June 22; 6 records, June 4 to 11.