Monday, October 1, 2012

Adirondack Wildlife: Osprey Exit the Park

As the temperatures in the many lakes and ponds that dot the Adirondacks begin to cool, the fish inhabitants of these waterways start to spend more of their time at greater depths. While this change in the routine of these gilled vertebrates impacts the way late season anglers pursue them, it also affects the life of our region’s most effective surface fish predator – the osprey.

With its 4 to 5 foot wing span and 2 foot long body, the osprey is a bird that is difficult to overlook as it soars over a picturesque mountain lake, or perches on the limb close to the shore of a pristine pond.

From the time it arrives in the Adirondacks in mid April, just days after the ice typically melts from our larger bodies of water until the time when the foliage is beginning to turn color, the osprey sits atop the food pyramid that exists in these aquatic settings. Like all raptors, the osprey has an exceptionally well developed sense of sight that provides it with a high resolution image of its surroundings, even from some distance away. In the case of the osprey, small surface disturbances created by 6 to 12 inch long fish cruising the uppermost zone of a lake or pond for food are most readily detected. Once this bird becomes aware of a target below, the osprey may immediately dive at the exact spot where it detected the subtle wave patterns made by the dorsal side of a fish in the hope of snagging a meal. This predator may also fly over that spot and hover in place for a dozen seconds or more in an attempt to gain a better perspective of what lies below.

With its long legs fully extended, the osprey is able to reach at least a foot below the surface to grab hold of prey without getting the bulk of its robust body too wet. Should conditions warrant, the osprey is capable of diving into the water with enough force to plunge to a depth of nearly 3 feet in an attempt to sink its talons into a fish and haul it from the water.

The return of weather that requires a fire in the woodstove also causes a dramatic reduction in the number of bugs that fly through the air just above the water or swim close to the surface. Without an abundance of invertebrates present in this upper zone, perch, trout, suckers and other fish common in our waters concentrate more of their foraging time in deeper locations, out of the osprey’s range.

As prey becomes more scarce during the final days of summer, the osprey departs our region and head toward their wintering grounds. Like other raptors, the osprey tends to migrate during the day, rather than at night and prefers to travel at thousands of feet above ground, rather than at an altitude of around a hundred feet. Also, rather than gather into a sizeable flock, the osprey is known to travel by itself, although it will remain close to other osprey encountered during a marathon bout of flight.

Because of its need for fish to eat, the osprey, like the loon, heads toward the seacoast after leaving the fresh waters of the Adirondacks. In bays, the mouth of rivers, sheltered coves and protected harbors, the osprey often finds the relatively quiet water in which it can more easily detect the movements of fish just beneath the surface. Within New York State, Long Island supports the greatest population of osprey because of the abundance of suitable fishing sites. During periods when a favorable northerly wind is blowing, the osprey works its way down the coast toward the tropics. Unlike the loon, which remains at mid-latitudes throughout winter, many ospreys continue to fly southward, traveling into the Caribbean or to the northern coastline of South America.

Once an adult osprey is able to find a wintering site that provides it with food, and is successful in establishing a breeding territory during the warmer months of the year, the bird can lead a long life. A lack of natural enemies allows the osprey to live for up to 20 years, with some individuals having an even greater longevity. This characteristic enables methyl mercury to accumulate more in the tissues of this predator than in most other fish eating birds. While there is increasing concern regarding the level of this toxin in loons, the osprey is just as prone to the neurological damage associated with mercury poisoning as are other fish eaters, like the mergansers and the kingfisher.

It is hard to judge how many fish any particular body of water contains, however, the presence of an osprey lurking near the shore of that waterway in summer speaks volumes about the number of fish residing in that aquatic setting. While some anglers view the osprey as a competitor, other sees it as an indicator of good fishing here in the Adirondacks.

Photos: Above, local osprey in a photo taken in July by Almanack contributor Justin Levine; below, the osprey breeding range in New York State (courtesy DEC). 

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Tom Kalinowski is an avid outdoor enthusiast who taught field biology and ecology at Saranac Lake High School for 33 years. He has written numerous articles on natural history for Adirondack Life, The Conservationist, and Adirondack Explorer magazines and a weekly nature column for the Lake Placid News. In addition, Tom’s books, An Adirondack Almanac, and his most recent work entitled Adirondack Nature Notes, focuses on various events that occur among the region’s flora and fauna during very specific times of the calendar year. He also spends time photographing wildlife. Tom’s pictures have appeared in various publications across the New York State.

2 Responses

  1. Tom, great column as usual. Two notes about ospreys:
    (1) your breeding map is already out-of-date as the osprey continues its re-population after the disastrous DDT campaign. They are, for example, widespread in western New York.
    And (2) an odd aspect of osprey breeding: newly hatched birds migrate to South America where they stay for two winters before returning.

    • John Warren says:

      Hi Gerry,

      Tom is off the hook on the breeding map. I pulled that from DEC.

      John Warren