Midwest Fish & Wildlife Conference 2018

AUTHORS: Kenneth L. Petersen, Bethel University; Steven Hogg, Three Rivers Park District; Judy Voigt Englund, Three Rivers Park District

ABSTRACT: For 3 decades, a restored population of Ospreys (Pandion haliaetus) nesting in the Minneapolis-St. Paul metropolitan area has used artificial sites nearly exclusively.  As the number of structures provided specifically for Osprey nesting has increased, so has the number of Ospreys using them, but with an apparent stabilizing of Osprey numbers over the last four years at 70-80 known pairs in the study area.  In 2000, Ospreys also began using “opportunistic” sites (structures not intended for nesting).  Since 1995, nesting success has ranged from 60% to almost 90%, averaging 76%.  Active nests have averaged 1.6 young fledged since 1995. Fledging success increased with the age of the male-female pair up to a combined age of about 20 years; at greater combined ages, success tended to decline.  We recorded 335 instances of a banded adult using the same nest site in successive years.  Mean fledging success for those adults was 1.84 in the prior year and 1.77 in the succeeding year.  We recorded 23 instances of a banded adult using a different nest site in the succeeding year.  In those instances, fledging success increased from 0.95 to 2.09.  Also, adults that moved to a different site in the succeeding year averaged 1.4 years younger than adults that used the same site in successive years.  Provided and opportunistic nest structures differed in some respects; opportunistic structures were taller and in locations with greater coverage of pavement and buildings.  But the two groups did not differ in fledging success.  The frequency of use of provided sites was negatively correlated with tree cover within 1 km of the nest and positively correlated with non-tree vegetative cover within 1 km.  However, fledging success showed little relationship with characteristics of the nest vicinity.