Twenty-thousand fish crows will meet up on two small islands at the mouth of the Alafia River tonight. Every healthy crow for miles around will be there.
The birds will begin rising from the southeastern shore of Tampa Bay a few minutes after sundown. They will form a thick black column and stream west across the water to their islands and the sun's last color. The swaying span will stretch from island treetops to roadside telephone wires and then disappear into dusk.
It will take minutes for them to pass overhead.
Some will swarm high over the island. Others will plunge immediately into the trees below. As the light dies, they will raise a raucous chorus of "caws" and "uh-ohs."
It may sound Hitchcockian, but it is just your average murder (or flock) of crows, one of about a dozen crow roosts in west-central Florida. Other murders, or large flocks, of crows will be acting out the same ageless behavior across the country.
The spectacles will be repeated every night until the crows disperse to their breeding territories, which in Florida is usually May. After the young have fledged, they and their parents will return to the communal roosts.
Why do crows gather in such numbers?
It probably helps protect them against their predators, according to Rich Paul, manager of Tampa Bay Audubon Sanctuaries. Raccoons, owls, hawks and falcons all like to eat them.
More significantly though, crows, along with ravens and jays, have the highest brain-size-to-body-weight ratio of all the birds in the world.
Many animal behaviorists consider this measurement a sign of relatively high intelligence. They think crows might use that extra brain power to develop and maintain bonds with other crows. Their mass roosting may satisfy a need for plenty of socializing.
But no one knows for sure.
Ted Below, a biologist with the National Audubon Society in Naples, has been monitoring a roost of approximately 3,000 fish crows for 10 years. They are the same kind of crow found in the Alafia roost. Most of the crows in Florida are fish crows, almost identical to the slightly larger American crow found in dryer ecosystems.
"Very little is known about fish crows," Below says.
Watching fish crows is not an easy job. They fly in such great numbers that biologists count crows by estimating groups of 100. Keeping track of individual birds within a murder is almost impossible, because crows will not tolerate being banded.
"They will tear their leg off if they can't tear the band off," Below says. "They will tear wing clips off, too."
Anyone who watches crows for any length of time quickly learns that they are very clever creatures.
The Suncoast Seabird Sanctuary on Indian Shores has sheltered its share of cunning crows. Cyndi Sandusky, an aviculturist at the sanctuary, says that crows there have learned to mimic human speech. It is a common trick among many species of crows.
"We had a crow named Ichabod," says Sandusky, "that called our outdoor supervisor to the phone. "Ernie, get the telephone,' he would say.
"Another crow _ Jeffrey _ learned to say "Let's go' and "right now.' I guess he has heard parents talking to their kids."
One captive crow at the sanctuary learned to pass food through the wires to free-flying crows on the outside. Nothing tangible gets passed back inside to him, so what's in it for the captive crow?
Ornithologists don't know why crows do what they do, but at least their behavior is often predictable.
The Alafia fish crows will disperse early in the morning to all corners of their territory. They may fly as far as 15 miles before beginning to feed. The birds will eat almost anything, including baby songbirds and squirrels, road kill, fruit, nuts, insects and garbage.
They forage all day, and begin working their way toward the roost during the afternoon.
Small bands join with others as they move closer to their islands. With each stop, or staging area, the flocks grow in size. Finally they all come together near the Cargill Fertilizer plant on the shores of the Alafia River.
A murmur builds as the last crows arrive. They adorn trees, buildings and utility wires as they await the mad rush to the island roost.
Despite its predictability, the crossing is different every night.
Sometimes a vanguard of a few hundred crows ventures out well before sundown. They will mix with resting pelicans, cormorants and other birds before calmly returning to shore.
The main crossing is not always completed on the first attempt. On some nights, hundreds of crows make several false rushes until the others join in. A small flock may even make it to the islands before realizing the others haven't come; then they turn and streak back to the mainland.
The first few thousand crows become very nervous if a hawk or falcon is perched in an island tree top. They break formation and swirl over the open water, unsure of carrying on or returning to shore. Eventually they settle on a path that does not bring them too close to their enemy, and the procession continues.
The singing begins as the last crows arrive. Perhaps it is a celebration of another successful day of foraging. Maybe they are warning predators to stay away. They could be defending personal space, or inviting friends to come closer.
No one knows, other than the crows, of course.
Mating season is the only thing that disrupts their routine.
Nesting crows do not join the big roosts and are very territorial. They will defend their nesting areas against all other crows. But even during the breeding season there will be immature birds that continue to roost on the islands.
All murders are not always so predictable. One in north Pinellas County recently disappeared overnight.
An estimated 3,000 crows had been roosting on a spoil island off Ozona's coast line. They have not been back since November, although large numbers still feed on holly and camphor berries only a quarter mile from the abandoned roost.
Where did they go, and why?
They may have joined a larger roost near the VA Medical Center at Bay Pines. Or they may have found a site elsewhere they liked better. Maybe the brainy birds just need a little variety.
Rich Paul, manager of the Audubon sanctuary that is home to the Alafia roost, offers that roosts are sometimes abandoned because of people shooting the crows. Increased predation will also drive them away. But neighbors of the Ozona roost have not heard any gunshots. And the presence of other roosting birds on the island seems to indicate that it is safe haven from predators.
Fish crows commonly share their roosts with lots of other birds. Ibises, herons and egrets are often found sleeping close by. Usually the crows are good neighbors.
But the Ozona murder, before it disappeared, was the scene of more baffling behavior.
On occasion, the crows would rise from the trees to mob and drive off an arriving pelican. All the other pelicans, in the trees or in the air, remained unmolested.
Pelicans are not known to harass crows, nor crows pelicans. Why the crows would target one hapless pelican is just one more crow quirk.
Maybe the crows were just having fun.
Dave Lowerre is a freelance writer who lives in Crystal Beach.
TO SEE THE CROWS
Williams Park, 9425 U.S. 41 S in Riverview, is the best place to watch the crows fly. Be there by sundown.