Good evening from the very soggy Eastern Shore! We received 3.25 inches, or 8 centimeters of rain this afternoon in a fairly short amount of time. Our osprey family looked rather bedraggled and wet, but they should be drying out soon. Chick #3 finally had an advantage over his older and larger siblings. He/she could fit easily under Audrey and stay dry. Numbers 1 and 2 were hanging out from under mom, without much coverage other than their heads. You have to take the good with the bad, kids! The weather has rapidly shifted from very warm and humid to cool, dry and breezy. The air conditioner is off, the windows are open and it sure feels good.
A couple of items of interest, then to the rest of Dr. Spitzer’s latest chapter. Last night, two of our Facebook followers commented on being able to see the nest due to the moonlight, and then commented on some flashes of light that could be seen on the ospreycam. There was a large thunderstorm passing to the north of us in Kent County, and we were able to see lightening flashes for quite some time during the evening. Great observation, ladies! On a clear night when the moon is full, you should be able to see the nest and occupants very well for most of the evening.
Around 1:00 p.m. this afternoon, Tom caught one of the biggest fish we have ever seen him catch! We saw him fishing, and then trying to head back to one of his favorite dining spots. He was struggling, and when we put the binoculars on him, we saw a huge fish in his talons. Tom was close to landing in the drink with his catch, who was still flapping around, when he managed to get to the perch off the end of our dock. The perch is about 18 inches across, and the fish was almost as long as the perch, probably at least a foot. The fish had a very deeply notched tail, so we are taking an educated guess that it was a large menhaden. Tom had a few bites, and then the rains came. We couldn’t watch for very long, but are sure that everyone in the osprey family eventually had a good meal off of Moby Dick.
Starting this week, another writer will be sharing blogging duties with me. She is a summer intern at the Chesapeake Conservancy who has lived her entire life on the Chesapeake Bay. In addition to filling you in on osprey activities, she will be writing about the osprey’s Chesapeake Bay environment and surroundings. Her insight and perspective should enrich your reading pleasure. I hope you enjoy her contributions to the blog.
Please don’t forget to vote in the “Name The Osprey” contest which closes tonight at midnight. Our chicks will be officially named tomorrow on the Conservancy’s Facebook page. Go to https://www.surveymonkey.com/s/6FCZFL7. Remember, one vote per person from the names selected during the Great Give.
Without further ado, please enjoy the continuation of Dr. Spitzer’s Ospreys Explained-Chapter #5 Osprey Population Dynamics or Life In The Osprey Garden:
During my 1980’s Chesapeake study I took a much more intensive approach, actually trapping the banded breeding ospreys. This was a great deal of pleasant work, and it yielded far more detailed data, such as the age distribution of the trapped sample. I spent the springs of 1983 and 1984 “fishing for ospreys”, which required patiently lingering in a johnboat on every creek and cove where they nested. Thus I explored the coasts of Talbot, Dorchester, Caroline, and Queen Anne’s Counties, and trapped 156 banded ospreys. Unknown to me, this was the beginning of the rest of my life in The Osprey Garden. By my count, Jan Reese of St. Michaels, MD, had banded 2,779 nestling ospreys in the years 1965-1980. Prof. Mitchell Byrd of William and Mary College and his students had banded similar numbers in tidewater VA during the same period. This was especially helpful, because it enabled me to look at long-distance dispersal across and up the Bay. Trapping along the Maryland Eastern Shore, I caught 16 breeding birds banded as nestlings on the Western Shore, VA or MD. All were females. I never trapped a male that crossed the Bay to breed.
One day I trapped a female on quiet little Leeds Creek, off the Miles River. The band number was familiar: One of my own. Scanning the Federal computer printouts, I realized I had banded that fledgling 11 years earlier in Connecticut, at the Millstone Point Nuclear Power Plant. It was on top of a 75-foot pole in that industrial area; a very professional lineman lowered it down to me in a canvas bag.
One of my casual “findings” was that the closer you got to Jan Reese’s house on upper Broad Creek, the more banded ospreys you saw, especially males. Broad Creek is a great, many-branched system off the north side of the lower Choptank River. On a nautical chart, its wide main stem and great dendritic profile with many big side creeks make it look like the old Wye Oak. It supports over 50 osprey nests, and careful survey of that colony on a torrid early-summer day is not for the faint of heart.
The age distribution of the trapped MD sample proved to be especially revealing and helpful. There were surprisingly few 3 and 4-year-olds (9 total), 5-year-olds were common (21), and my second year of trapping found five breeding 7 and 8-year-olds where I did not have banded birds the previous year. Considering the entire data set, I estimated the mean age of first breeding in this healthy, stable MD population to be fully two years older than in my 1970’s study of a remnant, low density population with abundant resources: 5.7 vs. 3.7.
Over the many years of his careful MD population study, Jan Reese counted active nests and fledglings, and published this data in scientific journals. His overall figure for productivity (young/active nest) was 1.14. This was after considerable nestling mortality and brood size reduction (chapter #3) had taken their toll. But I also had to consider the impact of two more years of pre-breeding survivorship, estimated at 85% annually, on this productivity. To get there, I multiplied 1.14 by 0.85 squared and got 0.8, a replacement rate similar to my previous northern study. Normal nestling and adult mortality, combined with deferred breeding, yielded a balanced and stable MD osprey population.
Deferred Chesapeake breeding implies intense competition for experienced mates and good nest sites, and I often witnessed that during my trapping study. In the brief period that I held one or both of the pair for processing, other ospreys would appear close by, sometimes attempting to land on the nest. (I assumed the territorial mantle and shooed them off.) In 37 cases, both members of the trapped pair were of known age, and that sample showed no statistical tendency for birds of similar age to be paired, no significant age correlation. This implies that experienced survivors were recruiting new breeders to quality nest sites: Once again, the “Osprey Culture” (chapter #2) was promoting the success of ospreys in humanized environments. The surplus of potential breeders would also push ospreys to try novel nest sites, such as high microwave towers. This successful adaptation is ongoing.
Ospreys’ relatively low replacement rate of 0.8, calculated from my years of study, has many implications. It explains ospreys’ rapid and tremendous population recovery post-DDT. This includes big breeding range extensions in man-dominated regions, and nesting “colonies” where abundant food and nest sites are available. It also helps explain ospreys’ world distribution, breeding in much of the temperate northern hemisphere and Australia.
The quality of any scientific hypothesis is measured by the accuracy of its predictions. We even have a struggling colony that proves the rule: “The Gardiners Island Anomaly”. This 3,000 acre glacially-deposited island lies between Orient and Montauk Points, NY. In much of the 19th and 20th centuries, it famously supported an osprey colony of 200-300 nests. For the last decade, it has struggled to sustain about 20 active nests, despite intensive nest-site management. Egg viability is fine, but nestling starvation is rampant. Gardiners is surrounded by many miles of open bay and ocean water. These marine habitats were a prime spring and summer destination for great quantities of migratory adult Menhaden, nurtured as juvenile fish in the Chesapeake and adjacent Atlantic waters. When they reach Gardiners Bay, these densely schooling fish are nearly a foot long. They filter-feed on plankton near the water’s surface, and are perfect prey for the osprey’s heroic dive. A great memory of my 1970’s studies on Gardiners is male ospreys toting blunt-headed silver-and-bronze menhaden in to nests clustered on a great beach meadow, their long forked tails shining yellow and translucent below the working bird.
Gardiners ospreys began a successful post-DDT recovery, rising to 70 nests, but this failed coincident with the collapse of Atlantic menhaden in the early 1990’s. There may be other ecological changes in the local food regime, but this “bioindicator” island osprey colony bears close watching. In the meantime, the Gardiners colony manages to fledge about 0.8 young/active nest, and thus survives at a subsistence level.
Paul R. Spitzer
Windy Hill on the Choptank
May 24, 2013
Great chapter, Dr. Spitzer! You are a true wealth of osprey information, and we appreciate your input.
That’s it for now from the slowly drying Eastern Shore. Until next time, we remain
Crazy Osprey Man and Mrs. Crazy Osprey Man
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