2024 OSPREY RESEARCH AND PRODUCTION SUMMARY
By Vanessa Greene
The 2023-24 winter was very dry with little snow so our first Ospreys in the spring of 2024 were observed on 3/31, followed by many others in the first two weeks of April. In my 31st year of monitoring Osprey nests in the eight county Twin Cities metro area, the known population was somewhat stagnant. The number of occupied nests monitored was almost the same as last year, with a slightly lower failure rate, and an increased mortality rate over last year. The summer started out with heavy early rains and the second half of the breeding season was hot and dry. The early Ospreys laid the first eggs by April 15!
There were 183 nests which were occupied* by a pair of adult ospreys. (182 in 2023). There may be more nests we do not know about and we hope the public will continue to report new nests to us. We discovered 9 new nests, but also had previously occupied nests that were empty this year. Eggs were laid in 169 active* nests (174 in 2023). There were 134 nests that had at least one chick that was confirmed to have fledged successfully or survived to fledging age (129 in 2023). We documented 49 nests which failed (53 in 2023, 35 in 2022). We separate failed nests into two distinct subcategories; there were 12 nests where a pair was present but no eggs were laid (9 last year) and 4 additional nests where we are not sure if eggs were laid or not.
There were 34 nests where eggs were laid but they failed to successfully fledge a single chick or the cause of failure was unknown (44 last year). (Not laying eggs is considered to be a kind of nest failure by other scientists.) Out of those 34 failed nests where eggs were laid, there were 20 nests where hatching did occur but all chicks died. There were 13 nests where no signs of hatching were ever observed. The 2023 failure rate dropped to 27%. This represents a slight decrease over last year! (in 2023 the failure rate was 29%, 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 257 chicks that were known to have fledged successfully or survived to fledging age! (253 in 2023, 264 in 2022, 295 in 2021). Most successful nests had two chicks this year, with 64 nests with two chicks, 30 nests with three chicks, and 39 nests that produced a single chick.
The known mortalities of chicks this year were higher than last year with 57 chicks which were known to have died or disappeared before fledging, (47 in 2023, 23 in 2022, 26 in 2021). In addition, there were 9 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, requiring them to travel further, and be gone longer when hunting. Many females were observed leaving chicks alone to help provide food. We had at least 8 single parent nests. Many lakes had high algae levels which made fishing difficult. These circumstances may have resulted in brood reduction, starving chicks and increased opportunities for predation. There were 7 known adult mortalities and 3 banded males that disappeared mid-season, (but did not show up at The Raptor Center.)
There were only 45 adult Ospreys identified by their bands, as the number of banded birds 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 6 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 9 new nesting territories with a pair present. Of these new nests, 5 of them successfully fledged chicks, with outcome unknown on 1 nest. It is interesting to note that of the 183 occupied territories this year, 84 were on osprey nesting platforms, 44 were on cell or radio towers, 29 were on ballfield lights, 21 were on a power pole or transmission tower, 4 were on other manmade structures and 1 nest was built in a tree
The oldest male this year, was 21 years of age, with one that was 19, one that was 18 years of age. ALL of these older males bred successfully! Our oldest female was 18 years old, with three that were 17 years of age and all bred successfully.
The overall productivity of occupied nests which were successful this year rose slightly to 74%! (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 dropped slightly to 1.92% (1.96% in 2023, 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 rose to 1.52% (1.45% in 2023, 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 rose slightly to 1.40% (1.39% in 2023, 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).
A small group of nests had the chicks banded with silver bands only. Three chicks received silver bands while in rehab, prior to release. In spite of many days of searching, and reading 14 silver bands, we were unable to locate any of these rehabbed chicks to confirm survival post release. We will continue to watch for them in future years.
It is interesting to note that we have recorded 3,773 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.
