Here are the data results for 2020, for those who are interested in the numbers!
2020 OSPREY RESEARCH AND PRODUCTION SUMMARY
By Vanessa Greene
The first Ospreys of the 2020 season were several territorial males that returned to their nests on April 1-2, with their mates returning the following week. The first birds to return were also the first to lay eggs on April 15. It was a good year for the Ospreys in the metro area in this 37th year of monitoring the osprey population in the eight county Twin Cities metro area, with increased numbers and a higher success rate than last year.
There were 159 nests which were occupied* by a pair of adult ospreys. (151 in 2019). There may be more nests we do not know about and we hope the public will continue to report new nests to us. Eggs were laid in 144nests (140 in 2019). There were four additional nests that were discovered late in the season with either no birds present (2), one bird present (1) or in one case, a dead adult osprey hanging on the side of the nest, which could not be included in the above counts without more information. Some of these nests may have been frustration nests. There were 116 nests had at least one chick that was confirmed to have fledged successfully or survived to fledging age (93 in 2019). We documented 43 nests which failed (58 in 2019). We separate failed nests into two distinct subcategories; there were 15nests where a pair was present but no eggs were laid (9 last year) and 28nests where eggs were laid but they failed to successfully fledge a single chick or the cause of failure was unknown (49 last year). (Not laying eggs is considered to be a kind of nest failure by other scientists.) Out of those 28nests where eggs were laid, there were 8nests where hatching did occur but all chicks died fairly early, before we could accurately count them. The remaining 20nests failed prior to hatching or for unknown reasons. This year’s failure rate reflects a significant decrease! The 2020 failure rate dropped to 27%. (In 2019the failure rate was 39%, in 2018it was 29%, in 2017it was 28%, and in 2016it was 25%.) We were encouraged to experience no repeat of the devastating black fly problems that occurred last year.
There were 237 chicks that were known to have fledged successfully or survived to fledging age! (194 in 2019). Most successful nests had two chicks this year, with 47 nests with two chicks, 37nests with three chicks, and 32nests that produced a single chick. The mortality rate this year was lower than last year with 8chicks which were known to have died or disappeared before fledging, (17 last year). There were two known adult mortalities. One was a female that was found injured below a nest in early April, was taken to The Raptor Center where she had to be euthanized. The other was the adult osprey found hanging dead from the side of a nest that was discovered in early September.
There were only 74adult Ospreys identified by their bands, as the number of banded birds continues to drop. We were sad to document that there were 18banded birds that did not return this year. Three of the returning banded ospreys were from Iowa.
We located 20new nesting territories with a pair present, including at least one nest that was newly discovered this year although reports indicated that they had been there for more than one year, and 11of these new nests successfully fledged chicks. There was one nest which was occupied by geese and one that was occupied by Great Horned Owls. It is interesting to note that of the 159 occupied territories this year, 75were on osprey nesting platforms, 30were on cell or radio towers, 26were on ballfield lights, 24were on a power pole or transmission tower, twowere on other manmade structures and twonests were built in a tree.
The three oldest males this year, were 17years of age, with two others that were 16 and 15. Of these five older males, two bred successfully, two others produced chicks that survived to an advanced age but did not fledge successfully, and one male failed to breed. Our oldest female was 14years old and she bred successfully. There were four females that were 13years old, which all bred successfully.
The overall productivity of occupied nests which were successful this year increased to 73! (62% in 2019, 71% in 2018, 72% in 2017, 76% in 2016, 68% in 2015, 70% in 2014, 67% in 2013, and 77% in 2012). The mean number of young fledged per successfulnest was 2.04%(2.09% in 2019, 2.13 in 2018, 2.25 in 2017,2.24 in 2016, 2.43 in 2015,). The mean number of young fledged per activenest was 1.65%(1.39% in 2019,1.64 in 2018, 1.75 in 2017,1.84 in 2016, 1.88 in 2015) and the mean number of young fledged per occupiednest was 1.49%(1.28% in 2019,1.51 in 2018, 1.62 in 2017, 1.70 in 2016, 1.65 in 2015). These numbers reflect a notable
increase in overall productivity per nest. There was one nest which has failed for six years in a row, but one nest that had failed for five years was successful this year!
It is interesting to note that we have recorded 2,704chicks that fledged from monitored nests since the inception of this project.
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*Successful nests are those that were known to have fledged at least one chick successfully, activenests are those where eggs are laid and occupiednests are those where pairs are present at a nest site for a period of time, regardless of the time of year or whether or not they lay.
