ON WING: What makes a bird down south starting thinking about
heading north for the summer?[neWLine]
Believe it or not, migration movements are set off by changes in
photoperiod – the amount of daylight in a given day – and, to a
lesser degree, weather conditions, such as a strong warm wind out
of the south.[neWLine]
We conclude today a report, “”Winging it Northward,”” written by
Joe Kosack, wildlife conservation education specialist for the
Pennsylvania Game Commission. The article focused mainly on
migrating waterfowl since their patterns make them a little easier
to spot than songbirds.[neWLine]
The urge to go north is triggered by increasing daylight hours,
although snow and frozen surface water will often stall or reverse
migration.[neWLine]
When winter lingers, waterfowl sometimes starts north before the
landscape can accommodate its needs. When birds that live on the
water can’t access it, they inevitably are forced back to the
south.[neWLine]
Winter’s conclusion is not decided by photoperiod, a groundhog’s
shadow or calendar progression. It lasts as long as natural forces
support it. Weather is erratic by nature and winter’s end is no
exception.[neWLine]
As a result, waterfowl migrations north are seldom as timely as
America’s holiday schedule, or as sequential as the days of the
week. In fact, they rarely go off without disruptions. But we can
surely ballpark waterfowl’s passage through Pennsylvania – always
under way in March – as confidently as we proclaim the start of
spring on March 21.[neWLine]
During migration, waterfowl species are believed to use the sun
and stars, as well as mountains, rivers and the coast to help guide
them. That’s why in foggy and rainy weather, waterfowl often ride
it out on the water until high pressure clears the air, and the
horizon.[neWLine]
Immature waterfowl learn migration routes and pit-stops on their
first trip south. The repetition of semiannual migrations seems to
help maturing birds stay on course.[neWLine]
But there’s something more to the guidance system of waterfowl
than terrain and celestial references. Some researchers believe it
may be related to the wind or the earth’s magnetic field. They
suspect these other navigational options come into play only after
visual referencing is impaired. Of course, there’s no way of
knowing for sure – yet.[neWLine]
Experts advise bird watchers to get afield when a warm front is
pushing through, and wear clothing to blend in with the
surroundings.
