Catch as Catch Can: Not Enough Food
Volume 2: Issue 11
September 1, 2022
Mattox Creek, VA
Pam Narney email@example.com
Osprey are survivors, an indicator species, a barometer of life in the Chesapeake Bay and global sentinels of aquatic health. Changes happening to Osprey and their offspring point to problems in the waters of the Bay because an Osprey’s diet is 99% fish.
Project Osprey Watch data shows the lowest number of young Osprey produced this year: 589. Also the lowest number of young produced per successful nest since 2012 was 1.8 this year.
The following observations suggest a problem in the fish supply.
Clutch Size Reduced
One indicator of limited food sources is brood reduction. The usual brood size for Osprey is three. This year only two chicks were born.
Brood size is determined by food supply. Brood reduction is a breeding strategy. “Adjusting breeding rates to food supplies allows Osprey to fledge the maximum number of viable young (who) survive to breed in their turn” (Poole).
If food can be a reason for sibling rivalry, this season has proved that point.
Sibling rivalry goes hand in hand with brood reduction.
“As in many other raptors (Newton 1977), sibling aggression in Ospreys seems to be an adaptation to ensure the successful fledging of an appropriate number of young during a period of food scarcity” (Poole 1979).
Well-fed chicks almost never fight (Poole 1979, 1982a).
In Mattox Creek, sibling aggression occurred when the chicks were 11 days old. When food is scarce the average time for aggression to appear is 10 days after birth (Poole).
The pecking and aggression, including one instance where Cassidy pecked, twisted Carla’s skin and shook her, continued steadily.
Sibling rivalry has increased in frequency over the years. Sibling aggression, in the past seen once in 10 years, has occurred in the last three nesting seasons.
Also, last year we had a runt. “Seeing runts or fighting chicks in an Osprey nest is … a good indicator that food is in short supply” (Poole).
Now there is increased aggression and competition for fish. Gracie delivers a fish to the nest and is mobbed. Cassidy, the most aggressive sibling, wins again and flies off with the fish.
Since 2011 we saw only three instances of aggression in the nest: last year, this year and once in the distant past. Before 2011 we weren’t able to observe closely. As years went by, we were able to observe more frequently and with more focus ending with 2022’s two weeks of dawn to dusk observations. We could have missed sibling rivalry, but it’s hard to ignore.
Feast or Famine
Another indicator of food stress might be changes in parental behavior patterns.
Mom will usually not hunt while still brooding the chicks. This year she often left the nest unprotected to hunt. Mom took over the hunting and feeding when George abandoned his post, last seen on July 6.
Most diurnal birds hunt at dawn and dusk because the chicks are hungry and it’s the best time to fish.
But this year, normal feeding patterns broke down. Feedings became erratic.
On a few days no fish were brought to the nest until after 2:00 PM, once after 4:00 PM. Some days there were five deliveries. Most days averaged three deliveries.
The fledglings and Mom were often seen digging or rooting around in the nest where the last fish had been. Perhaps they were hoping to find one last morsel of food, some remaining bits.
We had not noticed this behavior in other years.
The size and types of fish fluctuated drastically.
We saw fewer and smaller fish brought to the nest causing a decrease in duration of feeding times.
The sizes of the fish also varied widely. Two long periods of short feeding times and small fish were bracketed by deliveries of huge catfish.
Just after the eggs hatched, Dad brought a huge catfish to the nest. We didn’t see another huge catfish until the chicks fledged.
One day, Mom brought a fish the size of a cookie. Now, in late August, she brings whole menhaden.
Cassidy tries fishing from her perch. Twice she does a low flying catch and grab. Six more dives are also unsuccessful. Attempts seven and eight are straight down but from 15-30 feet. She catches no fish. Adult Ospreys dive from 30-120 feet high.high.igh.gh.h.
Although Clancy says that “raptors have occasional, large feeds separated by long periods of inactivity” (Corello, 2005), does the feast or famine approach to food provisioning affect the juveniles?
If so, how?
The siblings fought only when food was delivered. Cassidy and Carla thundered to the nest and ripped food out of their parent’s talons, nearly knocking them out of the nest.
On August 7, Mom flew by with a fish. Both chicks flew into the nest at speed, tangled with each other and landed in the water. It happened so fast I couldn’t get a picture.
Fewer and Smaller
Westmoreland State Park Chief Ranger Michael Such and local fisherman John St. John reported not only fewer fish this year, but also the fish they caught were much smaller. Many fishermen have given up and are not fishing. No longer can a fisherman throw croakers into buckets and see their tails stick out (personal conversation (8/2022).
Smaller fish are harder for Osprey to catch. More dives are needed to feed the juveniles the normal amount causing the parents to deplete precious energy.
Also, fish migrations were later than usual this year, perhaps due to unseasonably cold and wet weather. Osprey often time their arrivals to the menhaden population, a critical time when Osprey are starting to feed their young (Poole).
Osprey are now figuring in calculations in setting menhaden fishing rates (Poole, 2022). This year Chesapeake Bay striped bass and shad populations declined. Striped bass and bluefish depend on menhaden for the majority of their food, as do Ospreys (Chesapeake Bay.net 2022).
When schools of fish arrive in unpredictable pulses (Poole 70) chick growth and development may suffer.
July 24 Carla gets fish the first time Mom delivers it now. Is Cassidy fishing on her own?
August 14 Mom is still feeding the chicks sporadically. When she comes to the nest with food, she’s mobbed by Cassidy who grabs part of the fish and takes it to a piling to eat.
Carla follows Mom to the top of some tall trees and gets the rest of her fish.
Cassidy is spending less time in the nest, but Carla, always hopeful, still spends long periods of time in the nest begging and waiting for Mom and her fish delivery. Even though Mom’s deliveries are few and far between, they are still a sure thing. They are more reliable than Carla’s fishing attempts.
And then Mom brings an entire menhaden. Carla spends one hour and 45 minutes eating this fish.
Both chicks chased any Ospreys who carried fish. It is time for both kids to become proficient fish hawks.
Learning to Fish
Some juveniles have difficulty catching fish after they fledge. They have no experience and little practice. One way fledgling Osprey learn to fish is by watching other Osprey fish (Poole).
One day Mom dove and caught a fish right in front of the chicks as if to say, “See. This is what you do.”
She took the fish to a piling to eat her share while the fledglings put up quite a fuss, begging, and hopping around in the nest. When Gracie finished her share, both juveniles got fed.
July 26 My spin cycle faces Placid Bay, so occasionally my reward is an hour to watch Osprey antics. Once I saw both juveniles try fishing and diving.
Score: Fish 12 Osprey O
Cassidy tries fishing from her perch. Twice she does a low flying catch and grab. Six more dives are unsuccessful. Attempts seven and eight are straight down but from 15-30 feet. She catches no fish. Adult Ospreys dive from 30-120 feet high.
When Cassidy stopped, Carla tried two short dives and got nothing. Older more experienced Osprey often catch fish on two out of three attempts (Poole).
Both juveniles fished from the same spot, right under their tree perch in Placid Bay. They have not learned to hover from height to follow prey as it moves, making fish easier to catch.
Later that day Cassidy caught her own fish and took it to a perch to eat. Left out and hungry, Carla tried fishing again. She hovered, swooped, circled, and sort of dove, but caught no fish.
Some juveniles fish successfully as soon as they fledge. Inexperienced Osprey are more likely to catch an eel or snake than their more able parents. Very hungry adult osprey will also eat eels. Observations of Ospreys hunting and consuming other kinds of prey are extremely rare and have been linked with periods of hunger due to the scarcity of fish (All About Osprey).
Carla has a successful dive, but catches a snake, an eel? What is that? She is peeling it like a pepperoni sausage. Local fishermen identified her catch as an eel.
“Catch as Catch Can” is Carla’s mantra. She does the best she can.
August 29 Carla still comes to the nest each morning and at dusk. She lives in hope and old habits. Two fish deliveries a day are the norm now. She is always alone and begging.
Cassidy is self-sufficient now, out of sight and feeding on her own.
Mom brings Carla fish in the morning and at dusk. Each fish looks smaller. Around September 6 fish deliveries stopped. Mom has probably left on her migration. Carla will leave soon.
If the previous examples show a problem in the Osprey food supply, should we be concerned for the Bay?
What will the future hold?
Soon all of the Ospreys will be gone, focused on the next stage of their lives-migration to their overwintering grounds in South America.
Thank you for your time, attention, suggestions, and encouraging words. This is my last blog until the new season begins when the Osprey return in February.
Please send ideas for future blogs and Osprey questions to:
Pam Narney firstname.lastname@example.org
For a compelling description of Osprey migration read “Belle’s Journey: An Osprey Takes Flight” by Rob Bierregarrd with beautiful illustrations by Kate Garchinsky.
For information on migration go to:
Chesapeake Bay News. Chesapeake Bay sees health score decline by one point, but retain D+ grade. https://www.chesapeakebay.net/news/blog/chesapeake_bay_sees_health_score_decline_by_one_point_but_retain_d_grade
Clancy, G. 2005. The diet of the Osprey on the north coast of New South Wales. Emu 105:87-91.
Poole, A.F. 1979. Sibling aggression among nestling Ospreys in Florida Bay. Auk. 96, 415-17.
Poole, A. F. 1982a. Brood reduction in temperate and subtropical Ospreys. Oecologia 53:111-19.
Poole, A.F. 1989. Ospreys: A natural and unnatural history. Cambridge Press: Cambridge University Press.
Poole, A.F. 2019. Ospreys: The Global Revival of a Global Sentinel. Johns Hopkins Press. Baltimore, MD.
Poole, A.F. 2022. Colonial Beach, Virginia Osprey Festival 9 April, 2022, Zoom presentation.
Project Osprey Watch, summary yearly data. https://www.osprey-watch.org/summary