Monday, September 13, 2010

Weather & Climate

How it Affects Osprey Reproduction

2003 was one of the worst year's for osprey in New Jersey. Here is an excerpt from the 2003 New Jersey Osprey Project Newsletter:

"While the statewide average production was 0.86 young per active nest, it was somewhat better in Delaware Bay nests, at 1.09, than in Atlantic Coast nests, 0.73.  Productivity was depressed at all study areas, however, from Raritan Bay to Cape May to Delaware Bay.  Overall, productivity was down 27% from the 1997-2002 average of 1.18 young per nest.  This year it hovered close to the 0.80 young per nest considered necessary to maintain a population.

The most likely cause of this year’s nest failures is the weather during April and May, when ospreys were incubating and just hatching.  It was unusually cool and wet, and those conditions can have several implications for ospreys:  the high precipitation may have delayed fish migration and spawning, making prey harder to find; it may also have increased water turbidity, making it more difficult for ospreys to see fish.  As ospreys spent more time hunting with less success, their incubating partners may have been forced to leave the nest – exposing eggs or young chicks to weather and predators – to hunt for themselves.  In addition, we found that many young nestlings died when they were just two to three weeks old in June and early July, most from starvation, so the effects of the cool spring were far-reaching.  Unlike previous years when nest success declined in one region or another (primarily the Atlantic Coast), this year’s problems were statewide, which supports the theory that weather was the predominant cause." -- Kathleen Clark, Principal Zoologist, Endangered and Nongame Species Program.

Courtesy NJ Office of the State Climatologist.

No doubt we all know we had a HOT summer! It seems to have helped boost the osprey populations reproductive rate in all areas from Raritan Bay south to Cape May and west to Salem County, except for one area, Sedge Islands WMA. Its unclear why the Sedge population did not do as well this year. The productivity at Sedge varies from year to year, while the number of active nests has remained very similar (between 21 to 28 active nests from 2005 to 2010). Productivity peaked in 2008 and was at its lowest in 2003.

Courtesy NJ Office of the State Climatologist.

 A warm and dry climate will make nesting attempts more successful, while calm conditions will make foraging attempts more successful. Many bald eagle nests failed this year most likely from the wet conditions in February and March (when young nestlings are more vulnerable to harsh weather). Timing is everything. Osprey feed a variety of species of fish. Whatever is plentiful. This year menhaden was very plentiful off-shore. Boats from New England even came down to catch it for use as bait in the lobster fishery. Calm weather probably made it much easier to see and catch fish this year. Turbidity in water in calm weather is reduced so in-shore and off-shore waters were pretty clear. To be able to successfully raise young, male osprey need to supply a large amount of food to the female from coopulation through to when the young fledge (from early April to early-mid July). They need about 6 lbs. of fish a day to sustain themselves. Of 304 nests that were occupied (with a known outcome) 114 of them produced 3 or more young. Three nests produced 4 young. Outstanding results that will be summarized in the 2010 New Jersey Osprey Project Newsletter, which I'll be working on over the next week.

Osprey nestling giving Eric Sambol the stare down. © Eric Sambol.

On another note, we hit a whole bunch of milestones this year! Here's one: Volunteers and biologists surveyed more nests this year than any other year (when not conducting an aerial survey). 350 nests were observed as being occupied by a pair of ospreys. Previously the highest count was 288 nests. 70% of the population was covered this year! I just want to thank all our awesome volunteers who access many of these nests to band the young for future tracking and to all the other volunteers who report new nests in areas we don't routinely survey! Thanks!

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