Essayist Margaret Renkl writes in a recent column for The New York Times (July 7, 2025) that the Northern House Wren is "a tiny, feathered terrorist" because of its wanton destruction of the Carolina Chickadee nests (including eggs and young) that graced her backyard. Nevertheless, that explosion of blood lust failed to dampen her enthusiasm about this spring which was replete with young birds leaving their nests and making their way in the world. Amid her pleasure in the season, she grappled with myriad questions about the ways of the birds she observed (for instance, "Why did the baby cardinals leave the nest too early, still half bald and flightless?"), questions that brooked no easy, simple answers. It was this clutch of questions that prompted Renkl to posit that, whereas once she had little tolerance for unanswered questions or ones not answered quickly (e.g., the results of some medical test), "I am older now, and these days not knowing often feels like a gift."
At this point in the essay, she shifts from unanswered questions involving nature on a small scale or her own personal well being, to the more fundamental question of what will happen in the long term environmentally to the planet, with those in charge evincing little regard for the consequences of their actions. It's in the not knowing the outcome that she finds hope; the dire expectations haven't been realized yet, so, in the space between the now and the future, action might be taken. "I am grateful for the way that not knowing allows room for a future that is different from the one I fear."
I'm not grappling in this post with the long term environmental consequences of how people currently in power are intent on sacrificing the future for some short term payoff in the present. Rather, I want to share a couple of Renkl-like questions that have left me stumped. Over the past three years, I have been monitoring a small number of Ospreys each summer on the North Fork of Long Island. It wasn't until July of this year that I returned to my summer cottage and found that, of seven nests that were active in July and August of 2023 and 2024, three are vacant. By "active," I mean these were nests where, as best I could determine, short of climbing up to peer into the cavity, female birds were incubating eggs and the Osprey couple was subsequently feeding and tending to young. Nests I deemed "vacant" this year were ones without any Ospreys in or on them. Significantly, none appears to be damaged. I admit that I do not know if these nests were the scene of some nesting activity earlier in the season, and were subsequently abandoned before I started observing at the beginning of July.
In a post in 2023 I described an active nest very near my summer cottage that, despite the commotion visited on the it and its occupants by the passage of daily commuter trains, boasted healthy parents and robust, demanding young. It was also active in 2024.
Now it stands empty.
My first question was: What happened to the pairs that once raised young in this nest and the other two? My second was an attempt to place the experience of my nests into context: What's the expected year-to-year vacancy rate for Osprey nests?
I am unable to answer the first question with any certainty. Though Renkl suggests she has a willingness not to have an immediate answer to her nature questions, she did pursue some with a bit of determination. That's the case here. I do want to know the fate of my pairs, though, as I explain below, not having an answer leaves some room for hope.
The starting point, I guess, is that, as with nearly every kind of bird, the nest during the breeding season is the focal point of the Osprey's activity. The breeding pair becomes singularly attached to its nest, not only dedicating great time and energy to its construction, but, often, returning year after year to the same nest, repairing and adding to it. (See, for example, Alan F. Poole, Ospreys: The Revival of a Global Raptor, 2019, p. 80.) Which makes it puzzling why so many of the nests I'd observed over the past three years now are vacant, some even with vegetation now growing in them.
The factors that can influence why any single nest might be occupied one year and not the next are many. The most dire, of course, is that one or both of the birds that dedicated upwards of six months to it, perished on the several thousand mile long migration the Ospreys took to and from their wintering ground in the southern hemisphere. Alan Poole in his 1989 work on ospreys describes various ways of estimating the raptor's mortality rate. (Ospreys: A Natural and Unnatural History, 1989.) For large banded populations this may be a relatively straight forward calculation. He writes that preliminary data for two such populations offer estimated annual mortality rates of between 10 and 17 percent. (1989, p. 142) As I noted in my previous post on Ospreys, mortality in the earliest years of the bird's life is quite high: "Fewer than half of the birds that fledged will survive to breed." (For similar data, see, Hinterland Who's Who: Osprey, Minister of the Environment, Canada, 1993, p. 4.) The most dangerous periods in the bird's life are during the long migrations to and from the wintering grounds, and the wintering period itself. It's also the case that mortality rates are relatively low in early adulthood through late adulthood. (Federico De Pascalis, et al., Shift in Proximate Causes of Mortality for Six Large Migratory Raptors Over a Century, Biological Conservation, volume 251, 2020.) The percentage of absent breeding pairs in the seven nests is higher (at 43 percent) than the estimated mortality rates among adults just cited. This does make me question whether mortality, alone or at all, might account for these vacant nests.
Of particular relevance to my concern is Poole's observation:
Because most Ospreys are faithful to breeding sites, one can reasonably assume that any established breeder failing to return to its nesting territory (or nearby) at the start of the season has died. (1989, p. 142)
I then considered what might influence that decision. Is the relatively substantial human activity in the area around some of the nests I've been tracking discouraging Ospreys from returning? Likely not. Ospreys adapt readily to urbanized locations. A very interesting study on the factors that influence the success (not the presence) of Osprey nests in an urbanized Florida location found that it was principally the timing of the nesting activity which affected success rates (earlier nests fared better than later), not urbanization. Results from this study are affected by the fact Florida hosts migratory and non-migratory Osprey populations; the latter may nest earlier than the former. (Elizabeth A. Forys, et al., Predictors of Osprey Nest Success in a Highly Urbanized Environment, Journal of Raptor Research , Volume 55, Number 4, 2021.) The authors found no significant effect on nest success from the location factors they measured, including the nature of the land surrounding the nests - forests, grassy tracts, parks and ball fields, and "urban cover." They write:
In conclusion, this study provides further evidence that Ospreys can be productive in highly urban environments and this might be particularly true for areas like Pinellas County that are surrounded by water. (p. 493)
That conclusion rings true with my local populations. There is substantial human activity in this environment (e.g., repeated passage of commuter trains) which has not deterred Ospreys from nesting and nesting successfully in the area in the past, and there's been no obvious change this year in that activity. I would note that, after the 2023, breeding season, the local power company added a platform to the utility pole seen in the photographs above. That change to the pole in one year didn't preclude nesting in the following. Might this modification, nevertheless, have rendered the site sufficiently less attractive so the pair this year looked elsewhere? Perhaps.
It is possible that some threat to an Osprey nest is now present in the neighborhood, say a Great Horned Owl, though there's no evidence of that, and it's not clear why all three of the vacated nests were affected. As already noted, none of the nests appeared damaged, ruling out that potential deterrent to reoccupying a nest.
So, this first question remains unanswered.
As for the second, I tried to determine if the vacancy rate of my nests is unusual. It certainly appeared so to this uninformed observer. My journey through the research has not been very productive. Much of the research on Osprey nesting is focused on the success of the nesting activity (as is the one just cited for Florida). In contrast, if one asks the question regarding year-to-year use of a nest, there appears to be little data readily at hand. I've tried to tease out the answer to that question from data provided in various published sources, data not focused on the vacancy issue. I turned particularly to state projects monitoring Osprey nests, but, so far (the search continues), I have found only one with reported figures even tangentially speaking to my concern.
The Connecticut Audubon Society, in its 2024 report on the observations recorded by its Osprey Nation (a network of citizen scientists dedicated to monitoring and reporting on the state's Osprey population), noted that, in that year, there were "105 vacant platforms or comparable sites previously used." (Osprey Nation 2024 Season Report, November 8, 2024, p. 6.) If I read that description correctly, that's potentially the numerator I need - nests used previously, now vacant. But, what's the denominator?
Based on the data reported by the Society, the aggregate total number of nests observed in 2024 was 945. This includes 726 active nests, 31 nests that were removed or somehow destroyed, 83 abandoned nests, and the 105 vacant nests. That's not the appropriate denominator since the count of active nests includes ones newly observed that year, and some of the removed, destroyed, or abandoned nests might not have been used in prior years. ("Active" is defined as nests in which observers saw birds in the incubation posture or young not ready to fly.)
Recognizing that it's not wholly defensible, I turned to the prior year's count of active nests - 688 - and added it to the 105 vacant nests from 2024, to calculate a potential denominator of 793. That generated a vacancy rate in Connecticut in 2024 of approximately 13 percent.
If this is at all close to a reasonable year-to-year vacancy rate in my locality, then the 43 percent (3 of 7 nests) vacancy rate of my nests is dramatically higher. I recognize, though, that it's folly to draw any conclusions from data based on such an absurdly small sample. So, I will leave off, for the moment, the search for an answer to that and my initial question.
To end on a bit more of an upbeat note: even with nearby vacant nests, I have still been enjoying the piercing calls of Ospreys soaring high overhead while I work in the yard of my summer cottage or walk around the neighborhood, down to the beach, and along the road that abuts the marshy, reedy extension of the bay. There are Ospreys here and in number, some with nests that have escaped my detection. I have seen the raptors with plump, glistening fish in their talons, taking a meal to mates and fledglings in nests somewhere nearby. I hope my previous tenants are among them.
Another bit of good news. At some distance from my cottage, in the heart of the town of Riverhead, I found an Osprey nest new to me. What a beautiful sight, even with the unintended product placement.
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