Dear Journey North,
the email I've been receiving, it's obvious that lots of people
are concerned about the April 2007 cold snap and its effects on
the Ruby-throated migration. I don't have many specific answers
about this unusual event, but I do have a few theories and opinions.
The stage was set by an unusually warm early spring, with no significant
cold fronts during the entire month of March. As a result, although
the arrival of the first migrants on the Gulf coast was normal,
some birds made extraordinary speed northward with no bad weather
to slow them down.
my opinion, the spring hummingbird migration is constrained by the
availability of active insects, not by the blooming of flowers.
There were plenty of bugs for the earliest birds to eat. Freezing
temperatures are not a direct factor in hummingbird mortality (death);
healthy Ruby-throated tolerate nights in the teens easily, but freezing
weather limits insect activity. Hummers can do without nectar, but
they need bugs at least every few days or their nutrition suffers
(including their tolerance for cold).
the first week of April, a few birds had made remarkable progress,
particularly into the midwest, which saw unseasonable highs in the
80s. Everyone knew a cold front was long overdue, and it was a nasty
one, bringing thunderstorms, hail, sleet, and snow.
do not migrate in flocks. Each bird has its own internal clock and
migration schedule, probably inherited; the migration starts with
just a few individuals in early March, builds over several weeks,
then tapers off until it's essentially over by June. The dates on
the map reflect the earliest birds, not the vast bulk of the population.
Since they are spread out both geopraphically and in time, the species
limits its vulnerability to catastrophic conditions, including bad
weather. This is also why you may not see any hummingbirds for weeks
after the map shows sightings in your area. If a hummer passed through
a yard two houses away, you probably wouldn't notice.
a very small percentage of the Ruby-throated population had the
misfortune to be caught on the wrong side of the cold front. Will
they survive? There's little research to suggest answers, but I
would expect most individuals to find enough shelter and food to
manage, while some others will not. There's an advantage to being
first to arrive: a chance to claim the best breeding territories
— but there's always a risk of outrunning the food supply.
can you do to help? Don't wait to hang your feeders until
after you see hummingbirds. Let the map guide your timing. The standard
1:4 feeder syrup won't start to freeze unless nights drop below
about 27 degrees Fahrenheit, and even a slushy feeder is better
than none at all. You don't need to worry about insects or shelter,
because hummers are adept at finding both on their own.
heart-wrenching to think of hummingbirds dying from the cold, but
remember only a small portion of the population is affected, and
they're tougher and more resourceful than you might think. I'm more
concerned about what's happened to the wildflowers on which the
rest of the species will depend as they head north. The loss of
flower resources might have a much harsher impact overall than the
direct effects of cold weather on the leading edge of the migration.
Remember that many hummingbirds never use feeders, so try to replace
the freeze-damaged flowers in your garden as soon as you can.