Summary of 2015 research data...

The year 2015 was a successful year for the Ospreys in the eight county metro area surrounding Minneapolis and St Paul. Osprey sightings were reported as early as March 20, but the first Osprey positively identified was our second oldest banded male, at 22 years of age, back on his nest on March 31! This year must be characterized as a very productive one for the Osprey population in this 31 year study. The number of chicks rose dramatically as the number of nests increased somewhat. (There may be more nests we do not know about.) There were 110 nests which were occupied* by a pair of adult ospreys. One additional nest was thought to be a frustration nest and therefore not counted as a separate territory. Eggs were laid in 97 nests (89 in 2014) and 75 of these nests had at least one chick that was confirmed to have fledged successfully or survived to fledging age (71 in 2014). There were 35 nests which failed (30 in 2014). There are two distinct subcategories under failures; nests where a pair was present but no eggs were laid (10) and nests where eggs were laid but they failed to successfully fledge a single chick (25).  One of these nests was discovered late in the season, when it was not known if eggs were laid or not, but no chicks were ever observed. The neighbors reported that this nest had been active for many years, (though unknown to us until this year) with a pair present in the early spring.
There were 182 chicks that were known to have fledged successfully or survived to fledging age! This is a surprisingly high number compared to past years and it is noted that most successful nests had two to three chicks (29 nests with two chicks and 38 nests with three chicks) with only eight nests that produced a single chick and one that produced four chicks.  There was a moderately high mortality rate this year with at least 30 additional chicks which were known to have died or disappeared before fledging.  Four adults also died or disappeared midseason. There were 100 adult Ospreys identified by their bands. One of these was from Iowa, and one was from southern Ontario. There were 11 new nesting territories that we know of, including the nest that was newly discovered this year (mentioned above). Only three of these new nests successfully fledged chicks.

The overall productivity of occupied nests which were successful this year was 68%, (70% in 2014, 67% in 2013, 77% in 2012). The mean number of young fledged per successful nest was 2.43 (1.77 in 2014). The mean number of young fledged per active nest was 1.88 (1.41 in 2014) and the mean number of young fledged per occupied nest was 1.65 (1.25 in 2014).  These numbers reflect a significant increase in productivity per nest, especially in comparison to the drop in productivity noted in 2014. There was a notable cluster of ten nests which all failed within a small area, (approx five mile radius). The causes for these mortalities are not entirely clear. A few nests were harassed by eagles. At least one nest was a known predation, probably by Great Horned Owls, as the adult females headless body was found beneath the nest. We hope to increase the monitoring on these nests in 2016. Some losses in other areas of the metro can be attributed to a large storm on July 18. Two nests were completely blown down and all chicks died, and many other nests had some missing chicks after that storm. Our oldest male on record, at 23 years of age, died this year after returning late from migration. Our oldest banded female also died this year at 21 years of age from unknown causes. The banding program at Three Rivers Park District continued to be severely curtailed with only 15 chicks at six nests receiving bands.

(*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 whether or not they lay.)

Any use of this data should have its source appropriately acknowledged.
Vanessa Greene
Twin Cities Metro Osprey Watch