2023 OSPREY RESEARCH AND PRODUCTION SUMMARY
By Vanessa Greene
The 2022–2023 winter was long and very snowy, so the first Ospreys of the 2022 season were reported back on their nests on April 8, about a week later than usual. The first bands were read that day! In this 40th year of monitoring Osprey nests in the eight county Twin Cities metro area, the known population has continued to grow. There were more nests overall, with a higher failure rate, and much higher mortality rate than last year. This may be related to the extreme drought and heat experienced during the summer. The early Ospreys laid the first eggs by April 16!
There were 182 nests which were occupied* by a pair of adult ospreys. (167 in 2022). 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 174 active* nests (160 in 2022) which is quite a high percentage of occupied nests. There were only 129 nests that had at least one chick that was confirmed to have fledged successfully or survived to fledging age (132 in 2022). We documented 53 nests which failed (35 in 2022). We separate failed nests into two distinct subcategories; there were 9 nests where a pair was present but no eggs were laid (7 last year) and 44 nests where eggs were laid but they failed to successfully fledge a single chick or the cause of failure was unknown (28 last year). (Not laying eggs is considered to be a kind of nest failure by other scientists.) Out of those 53 nests where eggs were laid, there were 13 nests where hatching did occur but all chicks died. There were 15 nests where no signs of hatching were ever observed, and 16 nests where the timing of failure was unknown. The 2023 failure rate rose to 29%. This represents a slight increase over last year! (In 2022 the failure rate was 21%, 2021 the failure rate was 18%, 2020 it was 27%, in 2019 it was 39%, in 2018 it was 29%, in 2017 it was 28%, and in 2016 it was 25%.)
There were 253 chicks that were known to have fledged successfully or survived to fledging age! (264 in 2022, 295 in 2021). Most successful nests had two chicks this year, with 68 nests with two chicks, 28 nests with three chicks, and 33 nests that produced a single chick. The known mortalities of chicks this year were significantly higher than last year with 47 chicks which were known to have died or disappeared before fledging, (23 in 2022, 26 in 2021). Only one chick was known to have become tangled in baling twine this year and was taken to The Raptor center where it had to be euthanized. The causes for the high mortality rate among chicks are uncertain, but may be related to the unusually hot and dry weather. Many males seemed to be missing from nests more than usual, perhaps due to difficulties finding fish, requiring them to travel further, and be gone longer when hunting. Many females were observed leaving chicks alone to help provide food. These circumstances may have resulted in brood reduction, starving chicks and increased opportunities for predation. There were two known adult mortalities One was a 10-year-old banded male who was found on the ground not far from his nest, near a freeway, on April 15, and was taken to The Raptor Center where he had to be euthanized. Another was a five-year-old banded male who was found on the ground on May 6, not far from a nest where he appeared to be the new territorial male. He was also taken to the Raptor Center where he had to be euthanized. A third 17-year-old banded male was found injured and spent almost two months at The Raptor Center, and he was released on Aug 1, a long distance from his nest to prevent territorial fights since a new unrelated, unbanded male began bringing fish at this nest and providing parental care for chicks that were not his offspring. This is the first time a male has been this attentive to chicks that were not biologically his own in this project. The original banded male’s survival post-release could not be confirmed.
There were only 46 adult Ospreys identified by their bands, as the number of banded birds continues to drop. There were two additional adults with silver bands that were unable to be read. We were sad to document that there were 11 banded birds that did not return this year. Only one of the returning banded ospreys was from another state (Iowa).
There were 7 nests that were removed from cell towers over the winter. We located 14
new nesting territories with a pair present. Of these new nests, 8 of them successfully fledged chicks. It is interesting to note that of the 182 occupied territories this year, 85 were on osprey nesting platforms, 42 were on cell or radio towers, 31 were on ballfield lights, 20 were on a power pole or transmission tower, three were on other manmade structures and one nest was built in a tree.
The oldest male this year, was 20 years of age, with one that was 18, two that were 17 years of age, and one that was 16 years old. ALL of these older males bred successfully! Our oldest female was 17 years old, with two that were 16 years of age and all bred successfully.
The overall productivity of occupied nests which were successful this year dropped slightly to 71%! (79% in 2022, 82% in 2021, 73% in 2020, 62% in 2019, 71% in 2018, 72% in 2017, 76% in 2016, 68% in 2015).
The mean number of young fledged per successful nest dropped slightly to 1.96% (2.00% in 2022, 2.11% in 2021, 2.04% in 2020, 2.09% in 2019, 2.13 in 2018, 2.25 in 2017, 2.24 in 2016).
The mean number of young fledged per active nest dropped to 1.45% (1.65% in 2022, 1.78% in 2021, 1.65% in 2020,1.39% in 2019,1.64 in 2018, 1.75 in 2017,1.84 in 2016).
The mean number of young fledged per occupied nest dropped significantly to 1.39% (1.58% in 2022,1.74% in 2021, 1.49% in 2020,1.28% in 2019, 1.51 in 2018, 1.62 in 2017, 1.70 in 2016). These reflect the lowest numbers since 2019, when a large black fly hatch caused many losses.
It is interesting to note that we have recorded 3,516 chicks 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, active nests are those where eggs are laid and occupied nests 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.
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