Raptors of Disasters

The dinosaurs have been the dominant life form on Earth for most of the last 250 million years. The rose up on their hind legs in the Jurassic and marched off to rule the world – their skins shimmering with the iridescence of feathered scales. All the other animals retired into hiding from the dominant reptilians.

The reign of these creatures was interrupted three quarters of its way to the present by a cataclysmic mass extinction. All forms of animal life “larger than a bread box” – including all of the “non-avian” dinosaurs – met the end of their evolutionary lineages then. But the most aggressive of the reptile-derived lines, the flying raptors, continued their predominance into modern times.  They emerged from the end-Cretaceous extinction as feathered hunters smaller than a bread box, and, as the birds, they have been expanding across predator niches ever since.

The limitations of weight on flight have curtailed their maximum size – these feathered dinosaurs are no longer the largest creatures on the planet. But they are still by far the most numerous of the apex predators. Upon the open ocean, millions of sea birds still top the food chains. And the most numerous of the herbivores on land – the insects – have all perfected their camouflage strategies against the avian dinosaurs they know will be looking down upon all of their hiding places.

The insects have become so cryptic that a forest full of them looks empty, even while their calls fill the dusk. Only the lepidopterans, airborne and agile as they are, escape their feathered nemeses. Those butterflies and moths share the air with the modern flying dinosaurs.

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Today’s feathered raptors are specialists. Some of them specialize in disasters. These ones are poised to seize their earth-bound prey whenever the smaller forms are thrown from cover by local catastrophes. The birds look down like vultures, waiting to add further misfortune to the plight of their unfortunate prey.

The Rain Birds. Local disasters take many forms. Excesses of rain bring troubles for the creatures that hide at ground level or below. The rain puddles into pools, saturating the earth. Animals that burrow into or through the soil are drowned out of their concealment. Thrushes, black birds and jays are waiting to pounce when these smaller creatures are forced up for air.

Ponds and streams overflow their banks, and the waterline advances up and over the low ground. Creatures that live hidden under the deadfall on the earth find themselves collected at the advancing margin of a rising tide. The raptors stalk that margin. Crows and gulls gather to take advantage of the plight of the displaced. Wading cranes, herons and egrets flock to these situations – disasters for the lower forms, bonanzas for the feathered hunters.

The Fire Birds. Where the land rises and the season dries, fire replaces flood as the disaster that threatens the smaller creatures. The advancing front of a ground fire forces the insects, the small reptiles and mammals, and the smaller birds from cover. And, just as they stalk the advancing margin of the flood in other seasons, the raptors stalk that advancing wall of flames.

Cattle Egrets, falcons and storks look through the smoke and wait in the Australian out-back for their prey to flee to them. Ground hornbills and Secretary Birds on the African veld, caracaras on the Pantanal do the same. These raptors divide the advancing margin of fire, patrolling its edges, its front, the air roiled with rising thermals above it, and the charred track behind. The creatures that flee the flames have little time to regain the safety of cover when flushed by the fire.

The archetype fire bird is the Australian Black Kite. It follows the firelines across the brushlands, stooping on any creature that is driven into the open. Then, after the fire has run its course, the bird has been seen to perpetuate the flames by seizing a burning stick, carrying it away through the sky to a new location, and dropping it into more dry grass to start another fire.

The Ant Birds. The fiery wave that spills across the ground in the most productive of habitats is a living, breathing beast that flows on millions of tiny legs. Hordes of these stinging, biting pests are the scourge of the populations of creatures that flourish in the rain-forest tropics.

The advancing army flushes its prey from every surface. It rustles and sighs as it goes, like a relentless tide rising above the waterline. A particular scent rises from the advancing column, alerting creatures with sensitive noses. But its approach is most noticed by the raucous ruckus of ant birds that flock at the point of the army ants’ advance.

The ant birds are not eating the army ants. They are eating the ants’ prey. They pursue the small animals chased from cover by the invasion that flows through the niches of fallen leaves, down into burrows and up into trees. The birds steal from a stampede of running, crawling, hopping insects, spiders, centipedes, scorpions, skinks and snakes trying to stay ahead of the ground-borne assault.

Many of these birds are specialists, living in obligate association with the raiding ants. They stand aside, briefly taking wing if they find their feet crawling. Then they peer down from the foliage inches away from the action, waiting to pounce.

There are more species of birds exploiting of the waves of army ants than all the other bird species dedicated to the exploitation of all other waves of destruction combined. This is because the army ants in the New World, and the driver ants in the Old, are on the march every day, in every square kilometer of their tropical range. They are not seasonal or sporadic. They are reliable enough to support a dedicated guild of birds that prospers as their parasites.

The hundreds of species of antbirds have diversified into each of the niches that sustains army ants. This includes higher elevations, hilly up-lands vs. flatter lowlands, riversides, forest edges, and second growth jungle. These specialist birds all have different nesting strategies. Some supplement their diets by foraging away from ant raids. But all are alert to the sound of ants on the march, or to the calls of other ant birds who have found a march underway

The niche these birds exploit has brought them success. They make up less than ten percent of the tropical avifauna species, but their numbers can make up more than a quarter of the numbers of birds in areas where raiding ants occur.

 

Raptors of Disasters: notes. {This story is a precursor to “Ant Butterflies,” the first story in “Between the Rocks and the Stars.”}   The birds are the direct descendants of the warm-blooded dinosaurs. The flying dinosaurs reached maximum wingspans of thirty feet in the Cretaceous. The fossil record is incomplete about the smaller forms, which still predominate in the raptor niches today as the did. Maximum wingspans now are no greater than ten feet. The smaller forms have diversified into thousands of niches as the world recovered from the end-Cretaceous extinction. Many are still opportunists, ready to pounce in situations where their prey become exposed. The Black Kites of the Australian out-back have been reported to perpetuate the fires that flush their prey from the tall grass (Montague, 1970). This raises the possibility that once upon a time, at the dawn of human history, these firebirds by their example taught another animal about the handling of fire.

Montague, A. (1970) A remarkable case of a tool-using bird. American Anthropologist 72, 610