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Helpful Hints for Osprey Watchers

By Sergej Postupalsky

Optimum times for checking Osprey nests for:

  1. Occupancy/Incubation: mid-May
  2. Production/Number of Young: mid-July to the third week of July

In individual pairs, the timing of breeding tends to be quite consistent from year to year.  A new pair nesting for the first time, however, might be late by as much as three to four weeks. The same may happen if a mate change has occurred, and there is a new (young) female.

To determine if a nest has been repaired in the current nesting season, look for new sticks on top - sticks with fresh breaks.  This becomes important when no incubating adult is seen.

Photo by Jim KortgeIncubating adults may sit very low in the nest so that only the top of the head may be visible.  Sometimes not even that is visible. The trick is to whistle, clap one’s hands, or honk the car horn. The incubating bird’s head will pop up briefly to look around.

Later, if adults are present and defending, there is a high probability that young are in the nest. To see them may take some time.  Ospreys are very attentive and guard the young. One - usually the female - is almost always present.  When she becomes aware of an intruder, she’ll vocalize, and the young - even large ones as big as her - will flatten low in the nest and out of sight.

Therefore, it is best to watch through a scope from a distance or try to sneak up closer behind some cover.  It may take some time before the young come into view.  I’ve waited as long as an hour or more.  A youngster may stretch a wing or rise up to defecate.  The best one can hope for is that the male will come in with fish, in which case all of the young are likely to stand up - or at least raise their heads. One other way to tell if young are present is to look around the base of the tree or snag or platform for accumulated fecal matter. Much “whitewash”, including some that is fresh, will give an indication of the presence of young, but you won’t be able to see them until you’ve ut some distance between you and the nest, and the adult has quieted down and relaxed (in a sense sounded the “all clear” signal).

Adults can often be sexed in the field.  The female is slightly larger than the male, usually noticeable when they are standing or perched side-by-side. The female has heavier and darker brown blotching in her chest.  As a rule, the male has much less, and, if present, the spots are fewer, smaller, and paler. His chest may appear all white.  This works in about nine out of ten cases. Occasionally, one encounters a pair with the female’s spotting below average and the male’s above average; all of which will make them hard to tell apart.

Down young have a prominent white dorsal stripe. The stripe becomes covered when the chick develops body feathers at about four weeks of age. Nestlings can be thus aged as being less than four or greater than four weeks old.  In feathered young and fledglings, the dark brown body feathers are each edged with salmon or whitish color, give the bird a spotted appearance.  This and some tan feathers on the back of the head help to tell a fledgling from an adult - in reasonably good light, at least. Also, at about fledging time, eye color changes from brown to orange, but this varies between individuals. Young fledge - starting to fly - between seven and eight weeks of age, males a few days earlier than the larger, heavier females. This knowledge may help one judge if a missing young may have already fledged and left the nest.  Fledglings tend to return to the nest at feeding time when an adult comes in with food. In such instances, they may materialize out of nowhere.

Click here to read more about Sergej Postupalsky and his Osprey research.

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