Fratricide in the Osprey Nest
When you think about birds, do your thoughts turn to romance, or murder, perhaps? In the true story that follows, you do not have to choose. You will read about both. Join me on the hunt along the San Joaquin River in search of Osprey nests.
I’ve been captivated by Ospreys (Pandion haliaetus), magnificent fish hawks that nest along the San Joaquin River near Fresno,California, where I kayak every week. There is a fish hatchery near the put-in. During winter months I invariably see an Osprey perched on the upper branch of a leafless tree, patiently waiting for a meal to swim by.
Osprey diving for fish
Six or seven miles further down the river, an Osprey will occasionally circle overhead, then drop out of the sky like a scud missile. Seconds before hitting the water, it will thrust its legs forward to grab a fish. Unlike humans who hold their nose when jumping into the water, Ospreys have a closable valve in their nostrils to prevent water from entering airways. With spiny pads on its feet and reversible toes to securely grip a slippery fish, its success rate averages about 75%, far superior to the Bald Eagle whose fishing success does not compare. Once in the air, the Osprey may position its catch in line with its body to reduce aerodynamic drag. Catch or no catch, the sight of an Osprey is always a thrill.
Osprrey carrying fish under wings
I’ve often wondered just whereabouts these birds nest. Trees along the river prevent views of the landscape beyond the banks, and most of the adjacent land is private property. If only I could get a closer, more personal look at their daily lives.
Unlike birds of stealth, such as Cooper’s Hawks who are maneuverable in close proximity to tree branches where they lurk, Ospreys seek open space. Having a long, narrow wingspan (about 5.5 feet), Ospreys are adapted for flying in wide arcs. Open space facilitates landings and departures from their nest, and offers a clear view of the approach of aerial predators such as other raptors and ravens, as well as dangers on the ground.
Broad wings of Osprey in flight
While hiking in an area with public access, I came across a sizable nest atop the sheared off trunk of a long dead oak tree. Judging by its three foot diameter, I presumed it to be an Osprey nest. It was the only one I found in the one mile perimeter that I was able to explore. A stable platform capable of sustaining the weight of such a large nest is a rare commodity; it becomes the prized possession of its owner, to be defended at all costs.
As I looked around, I noticed a lone Osprey perched on a leafless branch of a small tree nearby. I was about to take a photograph when, all of a sudden, a second Osprey appeared out of the sky from behind, vocalizing loudly. It landed confidently on the back of the perched bird.
My initial impression was that I had just witnessed an attack. The behavior of the perched bird told me otherwise, though, as it displayed no objection to the bold intrusion. I had just seen a male Osprey mount a female.
Two Ospreys mating
Osprey romance is decidedly demonstrative. Males perform this mounting behavior throughout the mating season: during courtship and nest building, while eggs are being laid, even while the female incubates her eggs. Copulation happens frequently. In this manner, the couple confirms their pair bond, the female ensures all her eggs are fertilized, and the male knows that his genes, and none from another male, are the ones he will be protecting during the several weeks of the nesting cycle.
Typical of Osprey nest sites, it was free of obstructions all around. Better still, for me, I could observe it from an earthen berm that had been created by the excavation of a nearby abandoned rock quarry, now filled with water, as well as fish. Instead of craning my neck upwards from ground level, I was already one story up, which meant that I had an elevated view of the goings on inside the nest some 100 feet away. The location was convenient, too, being only a one mile fast walk from a public parking area.
Discovering this nest at an early stage in the breeding cycle of this pair was promising. Having witnessed the male mount the female, I knew egg laying would start soon, if it had not already begun. A month would pass before the eggs hatched, and then nearly two more months before any nestlings actually fledged. I’d have ample opportunity to observe the whole breeding cycle from start to finish, and that would be a unique experience to record. Everything seemed so easy and straightforward. What could possibly go wrong?
Unknown to me at the time, the discovery of this nest would set in motion a multi-year quest to witness what I considered to be the grand reveal of bird watching: seeing fledgling chicks leave the nest for their very first flight.
One strategy for the successful perpetuation of parental genes is asynchronous hatching of eggs. Unlike birds who postpone incubation until all eggs are laid (quail, for example) the female Osprey will begin incubating her first egg right away; then, incrementally, the others as they are laid. Spacing the hatching of eggs out over several days will, presumably, guarantee the survival of at least one offspring.
The first chick to hatch will have a head start over those who hatch two to four days later. Bigger, stronger, it may jostle the other nestlings, even peck them into submission, and thus monopolize food dispersal by the female. Studies on Osprey nest success report the survival rate of the second hatchling to be about 88%, while survival of the third chick falls dramatically to 38%. Limited availability of fish, resulting in fratricide by starvation, may also account for those results.
Danger to the nest is ever-present, both on the ground as well as in the sky. A corollary to the survival strategy exemplified by the above study might occur when the first chick to hatch (perhaps the only chick at the time) is picked off by an aerial predator.
Aerial attack over Osprrey nest
I witnessed such an attempt one morning when a rival Osprey flew low and directly over the nest. The female immediately took to the air in hot pursuit of the interloper. Had the depredation assault been successful, any remaining chicks would then each have had a greater chance of survival, again confirming the benefit of asynchronous hatching.
Osprey chases rival over nest
My observations of the three chicks in the nest followed a textbook sequence. The first two nestlings grew decidedly larger, while the third, whose head barely rose above the nest rim, struggled to be fed.
Felmale Osprey feeds her chicks video
On some occasions, I saw only two heads stretching upward to receive food from their mother’s beak. Days passed, and when the nestlings had grown large enough to become mostly visible, clearly there were only two remaining. Fratricide in the Osprey nest?
The goal of my bi-weekly visits was to be present when each nestling first took wing. It was an exciting prospect, as I envisioned it. Bad timing intervened, however. I left for a two week vacation; when I returned to the nest site, all was quiet, and nobody home.
I would return the following year, of course. Why not? The nest was a good one and I had an elevated view. I took care not to schedule any vacation time during Osprey nesting season. What could possibly go wrong this year?
With great anticipation, I walked along the berm. But I could not spot any nest, or any tree, for that matter. I was dumbfounded. Doubts about my memory stopped me in my tracks, and I looked around, mystified. It was then that I spied the trunk of the tree, toppled onto the ground below me. There was no evidence of any nest.
Fierce winds and ground-saturating rains that had pummeled our area over a period of several days during winter were the likely cause. When dealing with the natural world, as I was beginning to realize, best-laid plans often turn to fool’s gold. Once again, I put my vision on hold.
Lest one think my efforts at this nest site did not justify the time spent there, in truth I observed many exceptional moments that most people will never witness, events which make bird watching such an engaging activity. Standouts include the Osprey pair bonding behavior, the aerial predation attempt previously described, as well as a marvelous episode where a tiny Western Kingbird, its feathers all in a tiff for some reason, repeatedly mobbed the nesting Osprey, who ducked for cover and screeched vociferous alarm calls.
Western Kingbird mobs Osprey nest video
A Western Kingbird mobs an Osprey nest
In the broad spectrum of bird nest construction, from a simple, solitary scratch on the ground to an elaborate colony of elegantly woven grass basket nests (with, perhaps, a false entrance to foil predators) hanging from trees, Osprey nests fit somewhere in the middle. Because these nests are reused year after year, they change shape and might expand to over six feet wide and deep.
The nest is a complex assembly of sticks and branches of various length and diameter, with diverse pliable plant materials added for insulation, parasite containment, and simple fill. Typically, the male sources the construction material, while the female adroitly puts it in place with beak and talon. Just picture a male dropping off a pliable branch six feet long, and the female finding an appropriate place for it.
Male Osprey brings large branch to nest
Some nests are neat and tidy, while others, from a human point of view, are a haphazard jumble of matchsticks and Tinkertoy parts. Do you have what it takes to assemble an Osprey nest?
Neatly constructed Osprey nest
Two Adult Ospreys on power pole nest
Another twelve months elapsed. I happened upon Ospreys constructing a nest on, of all places, an electric power pole. With human encroachment upon land bordering rivers, power poles (as well as cellular towers) have become as ubiquitous as the homes and businesses they service. Securely planted into the ground, and having one or more crossbeams, it is no surprise that such frameworks provide an attractive structure that Ospreys have adapted to their nesting needs. These poles often work out well for the Ospreys. much to the dissatisfaction of the power companies.
The location of this nest, much to my satisfaction, was more easily accessible than the one I visited the two previous years. I could even drive my truck there, and park in the open space nearby. The truck would become my photography blind, and thereby reduce the disturbance my presence might cause the nesting pair. I began weekly outings, and was engrossed by the ongoing activity, particularly the frequent Osprey pair bonding previously described. Fratricide, such as any that might eventually occur, would be weeks away. What could go wrong this year?
After a brief hiatus to do work around my home in the foothills of the Sierra, south of Yosemite National Park, I returned to the nesting site. Words strain to describe my dismay at what I saw before me. Instead of a lovely, painstakingly constructed Osprey nest, in its place there was an enormous vessel that I would only kindly describe as a child’s backyard wading pool. There were two of them, actually; one on the nest pole, another on a second pole 100 feet away.
Nest supplied by utility company
What happened?
The attendant at a nearby bait shop related to me the following extraordinary chain of events. Due to arcing in the power lines, the nest caught fire, much to the consternation of the utility company. The company removed the charred nest and, apparently making no modifications to the pole fixtures, resumed power transmission.
The Ospreys, driven by their seasonal biological nesting clock, began anew. With options for finding a new abode limited, they resolutely built another nest on that same power pole. That second nest, reportedly, also caught fire, much to the displeasure of the utility company, and, presumably, the Ospreys as well.
This time around, though, the utility (most likely fearful of a wildfire raging through the area) had taken precautionary measures to prevent future fires should the ospreys resume their nest building. All well and good, perhaps. But active Osprey nests are federally protected, and should not be disturbed. Was the selection of this abominable gray tub influenced by the legal vagaries of this protection?
The Osprey pair clearly did not embrace nesting in a manmade container – one apparently without drainage holes to disperse rainfall, no less – and ceased their nesting efforts. I noticed a few sticks jutting out over the edge of the tub, though. Did the utility place them in hopes of enticing the Ospreys to return? The answer remains a mystery.
Still aspiring to witness the fledging of Osprey chicks, and wondering about those manmade nests, I returned to that location the following year. The gray tubs remained empty. and Ospreys were nowhere to be seen.
Propitiously, the bait shop attendant clued me in to an active nest along a nearby river trail. He pointed out the location on a map of conservancy property open to the public. There was even parking about a mile away; I could easily carry my camera equipment there. I might be too late, though, the attendant cautioned; chicks might have already fledged.
Encouraged by the possibility of observing another Osprey nest, I set out the next morning at sunrise. What could possibly go wrong this time?
As it turned out, the attendant at the bait shop was wrong about the status of nesting activity. In actuality, no chicks had fledged. In fact, incubation of eggs had only just begun. I was not late, after all.
Success was finally on the horizon, literally: a 100 foot power pole sat squarely in the middle of an expansive open space. Atop this skyscraper sat a ramshackle multi-story nest. No fire had ever occurred there. I could set up my gear anywhere I wanted.
Woman runner looking at Osprey nest on power pole
Being part of a public trail system, this area receives a constant procession of walkers, joggers, runners, and bicyclists; some photographers, too. Seeing me seated on a tiny, foldable stool, camera on a tripod pointed at the nest 150 feet away, people would invariably stop briefly to chat:
“What are you photographing?”
“What bird is that up there?”
“Is that a Bald Eagle?”
“Are you getting some good pictures?”
My favorite question was: “Did you know that you can get a better view from the other side?”
Yes, indeed, that observation was correct: the rim of the nest was lower on that side. However, I would be directly facing the sun during the early morning hours I was there, and my subject birds would all be in shadow.
Mid-July this year, nighttime lows were in the 67-68 degree range. By10:00 a.m., temperatures were pushing 90 degrees. No one asked if I was crazy enough to sit out in the noonday sun. I was always gone by 9:30 a.m.
Finally, at long last, in this riverside location, I knew my efforts to photograph an Osprey chick as it fledged would come to fruition. I had three chances, after all. How would they play out?
The first of the three nestlings left the nest a day earlier than I had expected. I spotted it the following morning perched on a branch, and two adults nearby, as I arrived with the sun reaching over the peaks of the Sierra behind me in the distance. Osprey chicks have orange eyes, while eyes of the adults are yellow, so I could tell who was who.
The following morning, a second nestling was ready to fly, and when it did, I captured the moment just as it launched into the air for the very first time.
Osprey fledgling takes wing for fery first time
A few days later, the third chick fledged.
That morning, I tracked all three fledglings as they explored their unbound surroundings … high up on a wobbly branch, lower down on a steady power pole, lower still on the stump of a felled oak tree, and even on the ground, obscured by the tall grass. There was no fratricide in the Osprey nest this year; only bird love.
It is hard to say what was the most memorable moment of this now concluded saga. Surprisingly, watching a nestling fledge was somewhat of an anticlimax after having witnessed so many fascinating life history events on the part of the adults and nestlings: courtship and romance, nest construction and maintenance, fish deliveries and feedings, chicks doing what chicks do in the nest as they grow … It was at once all new to me, then multi-layered as experiences accumulated over time.
Choose, though, I must.
Picture, if you will, nestlings flapping their wings. Tentatively, at first. Then, enthusiastically, as they develop strength and learn what they can do. And finally, energetically, with all the power and force their muscles can muster, so much so that they, to their surprise, suddenly rise above the nest, causing them to stretch their legs downward to grab ahold of the nest once more.
Seeing these nestlings flap their wings aroused in me all the anticipation one experiences while watching – on the edge of your seat, holding your breath – a gymnast perform a routine, twisting, rotating, spinning through the air, and hopefully sticking a landing.
Osprey nestling flapping wings learning to fly video.
Five years on the hunt, mission accomplished, at last. No storms. No fires. No fratricide. Only success in the Osprey nest.
Moon rising below Osprey nest
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