2019 OSPREY RESEARCH AND PRODUCTION SUMMARY
By Vanessa Greene
The first Ospreys of the 2019 season were observed on April 6, with reports coming in from various parts of the metro at the same time. The first bands were read successfully that day. The first signs of incubation were documented on April 19. This year was a struggle for many ospreys with a higher failure rate than past years in this 36th year of monitoring the osprey population in the eight county Twin Cities Metro area.
There were 151 nests which were occupied* by a pair of adult ospreys. (136 in 2018). There may be more nests we do not know about. There were five additional nests that were determined to be frustration nests which appeared after a nearby pair had failed to breed successfully, and therefore not counted as separate territories. Eggs were laid in 140nests (125 in 2018).There were also two additional nests that were discovered later in the breeding season and although no chicks were present, it was not known if eggs were laid or not and 93of these nests had at least one chick that was confirmed to have fledged successfully or survived to fledging age (96 in 2018). We documented 58 nests which failed (40 in 2018). We separate failed nests into two distinct subcategories; nests where a pair was present but no eggs were laid (9) and nests where eggs were laid but they failed to successfully fledge a single chick or the cause of failure was unknown (49). (Not laying eggs is considered to be a kind of nest failure by other scientists.) Out of those 49 nests where eggs were laid, there were 11nests where hatching did occur but all chicks died fairly early, before we could accurately count them. The remaining 38nests failed prior to hatching or for unknown reasons. This year’s failure rate reflects a significant increase so we looked at the statistical failure rate in recent years. In 2019the failure rate was 39%, in 2018it was 29%, in 2017it was 28%, and in 2016it was 25%. It was notable that a very large cluster of 20nest failures occurred in an approximate ten-mile square area surrounding Carver Park and the University of Minnesota Landscape Arboretum, near Victoria, Chanhassen, Chaska and Mound, MN. Most other failures occurred on scattered nests in the metro area. We do not know the reasons for these failures but in some cases, on these and other nests in other parts of the metro, we suspect that a large black fly hatch, after heavy rains, may have affected outcomes. Some adults were observed flying off the nest repeatedly during incubation. Swarms of black flies were seen on some nests with newly hatched chicks which probably succumbed to the constant biting.
There were 194 chicks that were known to have fledged successfully or survived to fledging age! (205 in 2018). Most successful nests had two chicks this year, with 41 nests with two chicks, 30nests with three chicks, and 22nests that produced a single chick. The mortality rate this year was similar to last year with 17chicks which were known to have died or disappeared before fledging, (19 last year) threechicks which died post fledge and twoadults which died; one from a vehicle collision and the other may have died from an impact injury after a territorial dispute. It was found dead near another nest on a cell tower with a severely broken wing. There were only 83adult Ospreys identified by their bands, as the number of banded birds continues to drop. Three of these were from Iowa. We located 13new nesting territories, including three nests that were newly discovered this year although reports indicated that they had been there for one or more years. Only four of these new nests successfully fledged chicks. There was one nest which was occupied by geese for the second year. It is interesting to note that of the 151occupied territories this year, 78were on osprey nesting platforms, 29were on cell or radio towers, 22were on ballfield lights, 18were on a power pole or transmission tower, twowere on other manmade structures and twonests were built in a dead tree. One of these laid eggs and produced two chicks who survived to an advanced age, but the nest blew down in a storm and both chicks died.
The overall productivity of occupied nests which were successful this year dropped significantly to 62%,(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 2.09%,(2.13 in 2018, 2.25 in 2017,2.24 in 2016, 2.43 in 2015, 1.77 in 2014). The mean number of young fledged per activenest was 1.39%, (1.64 in 2018, 1.75 in 2017,1.84 in 2016, 1.88 in 2015, 1.41 in 2014) and the mean number of young fledged per occupiednest was 1.28%,(1.51 in 2018, 1.62 in 2017, 1.70 in 2016, 1.65 in 2015, 1.25 in 2014). These numbers reflect a notable decrease in overall productivity per nest. There were two nests which have failed for five years in a row.
The four oldest males this year, dropped to 16years of age, with two others that were 15. Of these six older males, only two bred successfully. Our oldest female was a banded female that showed up on a nest this year for the first time and she was 13years old! This indicates that she must have been nesting previously in a territory that we don’t know about! She bred successfully. There were four females that were 12years old, three of which bred successfully.
It is interesting to note that we have recorded 2,467 chicks that fledged from monitored nests in the eight county metro area since the inception of this project in 1984.
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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.
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