We received a lot of “First of the Year” Swallow-tailed Kite
sighting reports on 2/24/2016, and it’s no wonder after a look at the following
wind maps. The arrows show the wind directions around two high-pressure systems
that were moving from west to east (left to right) on 24 and 25 February. The
air in a high-pressure system always circulates clockwise and outward, whereas
the air in a low flows counter-clockwise and inward. The more “feathers” on the
wind arrows, the faster the winds.
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Map 1. 11:00 Eastern
2/24/16
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On 2/24 (Map 1), a high that had just passed into the eastern
Gulf of Mexico was producing southerly winds (i.e., blowing from the south)
over the Yucatan Peninsula. This would have encouraged kites staging on the
northern Yucatan to begin flying northward. By late morning on the 24th,
as this high was leaving the Gulf to the east, it was being replaced by another
high approaching from the west. The clockwise-and-outward flow around this
second, approaching high produced strong westerly winds across the northern
Gulf of Mexico, which blew any northbound Swallow-tailed Kites in that area directly
toward the Florida Peninsula (Map 1). This
explains the sudden up-turn in sightings in Florida on the 24th. For
the previous 15 days, northerly winds had dominated the region. Most of the
birds reported in peninsular Florida on the 24th probably had just
reached land.
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Map 2. 07:00 Eastern 2/25/16
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But wind directions and velocities are continuously
changing, and they change particularly fast over the Gulf of Mexico. Just 20
hours later, at 7:00 a.m. on 2/25/2016 (Map 2), the same high had shifted
farther to the northeast and was now creating steady northerly winds from the
southeastern U.S. southward across the Gulf and deep into the Yucatan
Peninsula. This would have discouraged any kites still on the Yucatan from
migrating northward. They were safe as long as they stayed on land.
This could not be said for the Swallow-tailed Kites - and
all the other northbound migrants of many species - that had already struck out
over the Gulf. These birds were now facing solid headwinds. Some that were
already close to Florida may have gotten blown far enough south or southeast to
encounter Cuba and survive. But we know
from our satellite-tracking studies that many northbound Swallow-tailed Kites come
to a virtual stand-still out over the Gulf, turning in circles awaiting a change
in the winds that will help them reach shore. We have learned that they can
remain aloft over the water for three to four days. Most northbound kites will
experience favorable winds in time and reach land. The rest will perish.
