Each spring, I await the return of one particular raptor with particular anticipation, the Osprey. Always around the first of April when the ice has disappeared, they re-appear to their platform nests that sit atop numerous snags along the rivers and lakes of western Montana. All at once, there seems to be a pair occupying every available nest site. They are returning from Mexico and Central American where they spent the winter plunging into warm, tropical waters for their meals. The sheer numbers of Osprey can make seem as if they are an incredibly common.
This was not always the case. When I was a small kid around 1980 – I am starting to feel old – I remember when the first Ospreys returned to the Clark Fork River near Plains. I can still see that bird in my mind’s eye. During the years preceding this first observation, Osprey populations had declined significantly due to DDT, which caused thinning of the egg shells causing them to break easily. DDT was used of mosquito control through the 1940s to the 1970s, when it was banned from use in the United States. As most people know, Rachel Carson’s Silent Spring (1962) cast a monumental light on the various detrimental effects of introducing organochlorine and organophosphate insecticides into the environment. With the bans, Osprey populations began to rebound across North America. I remember how large that first Osprey seemed to my small eyes. Its wings covered the sky as it leapt from a cottonwood snag near the river. My father told me it was an Osprey, and upon learning that one word, I was hooked by the proverbial talons of this raptor.
Raptor is an odd moniker to place on the Osprey as it is radically different any of its relatives. While it looks superficially like an eagle, it is quite different structurally. The feet of Osprey are particularly well evolved to deal with catching fish, which make up the entire diet of the bird. The bottom of the toes are covered with spicules – little fleshy spikes that help the grip on a slippery fish. The arrangement of the toes is called zygodactyl, meaning that the first and fourth digits are back and the second and third digits are forward. This arrangement of digits creates grappling hook effect that grips tightly on fish with two digits on either side. This digit arrangement is not found in any other member of Accipitriformes (birds of prey other than falcons). The talons of the Osprey are rounded in cross-section, rather than the grooved talons of all other birds of prey. The talons are ideally suited to perched the scales and tough skin of fish.
Taxonomically, the Osprey is an enigma with its variety of unique physical characteristics. and so it is placed within its own monotypic family, Pandionidae. There are 4 acknowledged subspecies of Osprey across its immense cosmopolitan range, which includes every continent other than Antarctica. But, these 4 subspecies may actually constitute 2, 3, or 4 full species (depending on your source).
“Pandion haliaetus, as currently recognised, has a cosmopolitan distribution (Poole 1994). Genetic distances (based on almost complete nucleotide sequences of the cytochrome-b) between subspecies of Osprey (1.9-3.8%) are equivalent to, or greater than, those seen between members of several closely related sister species within Aquila and Hieraeetus (Wink et al. 2004a). This, combined with small, but consistent, differences in plumage and morphology, led Wink et al. (2004a) and Wink and Sauer-Gürth (2004) to suggest that three species of Pandion could be recognised. Acceptance of this recommendation means that Australian birds become Pandion cristatus (Eastern Osprey).” – Christidis & Boles 2008
At Lee Metcalf National Wildlife Refuge yesterday, 7 Ospreys were vying for two adjacent nests, in the form of man-made platforms placed atop of a couple of snags near the ponds. They would circle one another and engage in battles without ever making contact. The wind blew strongly across the landscape, and the snags swaying heavily. The larger of the two seemed to be in danger of toppling over at any moment, but this did not stop an Osprey from landing on the platform and hunkering down. I admired this trust in a structure of seemingly dubious integrity. As the wind cycled through periods of calm, one Osprey made several diving attempts at the fish in the pond. It streaked through the sky several meters in front of me, and I reeled off hundreds of shots in the hope of obtaining at least one decent image. The Ospreys have returned to western Montana in terms of this year and historically.