2025 OSPREY RESEARCH AND PRODUCTION SUMMARY
By Vanessa Greene
The 2024-25 winter was very dry, with little snow, so our first Ospreys in the spring of 2025 were observed on March 27, followed by many others in the first two weeks of April. In my 32nd year of monitoring Osprey nests in the eight county Twin Cities metro area, the known population remained somewhat stagnant. The number of occupied nests monitored was almost the same as last year, with a higher failure rate, and a slightly decreased mortality rate over last year. Ospreys laid the first eggs quite early, on April 12!
There were 184 nests which were occupied* by a pair of adult ospreys. (183 in 2024). There may be more nests we are not aware of, and we hope the public will continue to report new nests to us. We discovered 13 new nests, but we also had previously occupied nests that were empty this year. Eggs were laid in 167 active* nests (169 in 2024). There were 127 nests that had at least one chick that was confirmed to have fledged successfully or survived to fledging age (134 in 2024). We documented 57 nests which failed (49 in 2024, 53 in 2023, 35 in 2022). We separate failed nests into distinct subcategories; there were 16 nests where a pair was present, but no eggs were laid (12 last year). There were 40 nests where eggs were laid but they failed to successfully fledge a single chick (34 last year), and one nest where the cause / timing of failure was unknown. (Not laying eggs is considered a kind of nest failure by other scientists.) Out of those 40 failed nests where eggs were laid, there were 21 nests where hatching occurred, but all chicks died. There were 19 nests where no signs of hatching were ever observed. The 2025 failure rate rose to 31% (27% last year). This represents a slight increase over last year. (in 2023 the failure rate was 29%, 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%)
There were 245 chicks that were known to have fledged successfully or survived to fledging age, the lowest number in the past 5 years, (257 in 2024, 253 in 2023, 264 in 2022, 295 in 2021). Most successful nests had two chicks this year, with 56 nests with two chicks, 31 nests with three chicks, and 40 nests that produced a single chick. The known mortalities of chicks this year were slightly lower than last year with 55 chicks which were known to have died or disappeared before fledging, (57 in 2024, 47 in 2023, 23 in 2022, 26 in 2021). In addition, there were 10 nests where signs of hatching were observed, with adults feeding chicks, but they all died before we could get an accurate count. The causes for the increasingly high mortality rate among chicks are uncertain but may be related to climate change. Many males seemed to be missing from nests more than usual, perhaps due to difficulties finding fish, as many lakes had very high algae levels. We had 2 single parent nests, which were caused by two polygynous males that were initially going between two nests. Eventually both males ceased attending one of their nests. This resulted in one female giving up during incubation, and her nest failed. The other female continued to incubate alone when her new male disappeared about a week after eggs were laid. She left for very short periods to catch a fish and ate quickly on the nest edge. She managed to hatch two chicks, but one died after about 10 days. One chick fledged successfully. There were 2 known adult mortalities.
There were only 36 adult Ospreys identified by their bands. There were 27 Ospreys with color bands and 9 with just silver federal bands. The number of banded Ospreys continues to drop.
There were four additional adults with silver bands that were unable to be read. We were sad to document that there were 9 color banded birds that did not return this year. Only one of the returning banded ospreys was from another state (Iowa).
There were 6 nests that were removed from cell towers or lights over the winter. We located 13 new nesting territories with a pair of ospreys present. Of these new nests, 6 of them successfully fledged chicks. It is interesting to note that of the 184 occupied territories this year, 85 were on osprey nesting platforms, 47 were on cell or radio towers, 29 were on ballfield lights, 18 were on a power pole or transmission tower, 5 were on other manmade structures.
The oldest male this year, was 20 years of age, with one that was 19, one that was 18 years of age. All three of these older males bred successfully! Our oldest females were two 18-year- olds, with one that was 15 years of age, and all bred successfully.
The overall productivity of occupied nests, which were successful this year, dropped to 69%! (74% in 2024, 71% in 2023, 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 rose slightly to 1.93% (1.92% in 2024,1.96% in 2023, 2.00% in 2022, 2.11% in 2021, 2.04% in 2020, 2.09% in 2019, 2.13 in 2018).
The mean number of young fledged per active nest dropped to 1.47% (1.52% in 2024, 1.45% in 2023, 1.65% in 2022, 1.78% in 2021, 1.65% in 2020,1.39% in 2019,1.64 in 2018)
The mean number of young fledged per occupied nest dropped slightly to 1.33% (1.40% in 2024, 1.39% in 2023, 1.58% in 2022,1.74% in 2021, 1.49% in 2020,1.28% in 2019, 1.51 in 2018).
It is interesting to note that we have recorded 4018 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.
