It’s that time of year when the birds are getting restless. Migration is stirring in their bones — hollow bones evolved for long-distance flight. We expect thousands of Vaux’s swifts to roost in the old Agate Hall chimney for a week or so on their way south. Watch for the Audubon Society’s Friday night vigils Sept. 20 and 27 when that happens.

The equinox on Sept. 22 comes as the change in day length is at its greatest. After equinox the rate of change decelerates until the change is barely noticeable during the season of longest nights.

Like birds, seeds are dispersing. The ones with tiny, barbed hairs may be the most noticeable. They bind tightly to socks and twist up tough knots in long-haired dogs. These are known as hitchhikers. Other seeds use temptation for dispersal, being buried in a fleshy coating that attracts birds like robins and cedar waxwings. The birds swallow the fruits and then deposit the seeds far and wide.

In 2009 there was a massive production of California black oak acorns but not Oregon white oak. This year there’s a bumper crop of both. Known as masting, an overproduction squirrel and jays can’t keep up with, more are buried than are likely to be used. Popular lore maintains that squirrels forget where some were buried and those germinate to produce seedlings. The truth is they don’t have a bad memory; seedlings abound when hawks thin the squirrel population. All the acorns buried by thinnings are free to grow.