An osprey does not express his love quietly. He screams it in decibels as sharp as glass shards that carry for miles. He does not proclaim his love from the rooftops, but from several hundred feet above the rooftops. And it’s not all just proclaiming. There’s a lot of hovering, as well as swooping, diving and climbing. And it usually involves a fish, gripped in specialized talons, though that’s tough to see from the ground. All that drama can come off as formalized and indecipherable as a German opera – though performed at a much higher octave – with more sturm and drang than you’d expect from a 4-pound bird with a 5-foot wingspan.
As with a lot of avian mating rituals, the craziest thing about it is: it works. And it has worked for thousands of years. If the performance pleases her, a female osprey will give her assent and the two will spend the next four months bringing a clutch of chicks out into the world. (They may copulate up to 130 times in the process, but they generally produce two to four eggs.)
Osprey are some of the most widely distributed raptors in the world, found on every continent except Antarctica. Though they sometimes winter in South America, they don’t breed there.
While most birds have some kind of descriptive term attached to their name, osprey are one of the bird world’s few mononyms. Like Cher, Madonna and Bono, their whole name is the single word. The name mutated from the Old French “ospreit,” which somehow mutated from the Latin “Avis praedea,” meaning bird of prey. But the name also mutated from the Latin “ossifrage,” which means “bone breaker,” because osprey look kinda sorta like bearded vultures who have a habit of picking up the bones of dead lambs, flying them up to a great height, then dropping down onto the rocks to crack them open and gain access to the marrow. Even though that’s not what osprey actually do. (Etymology and early natural history are not always precise sciences.)
Almost any paper you read about osprey will say they are nearly pure piscivores, with fish being at least 99% of their diet, but that 1% is probably something of an overstatement. One hundred percent is not a number scientists are generally comfortable with. There are reports of them occasionally eating snakes, very young alligators, or small mammals, but those are nearly always anecdotal.
As a result, osprey are occasionally called fish hawks or sea hawks (as in, the Seattle…).
Osprey fish by diving, usually from 30 to 120 feet up. They spot their fish from on high, often while hovering, then fall, talons out in front of their face. Sometimes they snag their fish in the top few inches of the water and haul them out seemingly without breaking their momentum. Sometimes they will dive as deep as 3 feet. The fish they catch are often 10% to 15% of their body mass.
Everything about their bodies works toward the goal of snagging fish from the water. Their feathers contain an oil that makes them water-resistant, though not waterproof, so after a series of dives they often have to perch and dry them out. Their eyes – a rich golden yellow – have nictitating membranes that slide over them like translucent protective curtains when they hit. Their nostrils can close to keep the high-pressure water from a splash from going into their respiratory system.
Their feet are large, muscular and double jointed, with long, sturdy talons that can pierce and grip their slick and often thrashing prey. Their wings have a telltale kink in the wrist and are long enough to seem almost rubbery when seen flapping from a distance, the length providing the power they need to pull the fish out of the water.
Once in the air, the flexibility in their joints allows them to turn the fish face forward, and it can often look as if they are riding a surfboard or a torpedo. They usually perch somewhere nearby and begin to devour their prey quickly. They tend to save the tail for last and often abandon it.
Because of all this, an osprey’s main environmental requirement is open water. In most of North America this means they fly north in the summer to breed, then south in the winter to avoid ice. As ice is not an issue in Florida, our populations tend to be non-migratory, and here they breed in the winter.
Most courtship tends to happen in December and early January. Hence all the aerial theatrics around here this time of year.
On the mainline Keys, osprey often use manmade structures for nesting. You see nests on radio towers, telephone poles and channel markers. But you also often see them on structures specifically constructed to be osprey nests – usually an old telephone pole with about a 4-foot-square platform on top.
In the backcountry they will often build nests in the mangroves and, occasionally, directly on the ground.
Mostly they build nests out of sticks, but will occasionally include manmade objects such as plastic bags, rope, nylon mesh bait bags and, in the Keys, the occasional bra or scrap of an American flag. Fishing line is also sometimes incorporated, which can be hazardous, as chicks can get fatally entangled.
A study done in the late 1980s showed that osprey had the highest breeding success in the Upper Keys when they nested on manmade structures, rather than on the undeveloped islands in Florida Bay. While that may lead you to think manmade structures were superior, those success rates leveled out between the mainline islands of the Lower Keys and the backcountry islands south of Marathon, which leads me to believe it wasn’t the structures that made the difference, so much as the fishing grounds.
Osprey seem to have adapted well to breeding around humans.
When at Fort Zach a few weeks ago, a pair looked to be nesting on the pole across the field in the northwest corner of the park. It wasn’t clear exactly which part of the breeding process they were in, but hopefully they’re going to move beyond the drama soon and we might all get to see them raise a couple of chicks.
