Blog #477 Spring Arrival
Spring arrived tenuously in the Finger Lakes in late March as Ospreys returned from their arduous 3–5-thousand miles spring migrations exhausted, hungry, and looking for their nests. Ospreys migrate as individuals but reestablish their colonies as soon as they reach their breeding grounds. Hundreds of Ospreys settle into their nests and begin refurbishing their homes with fresh branches and twigs. By May most nests will be reclaimed, and new nests will extend north toward Lake Ontario and east and west of Cayuga Lake.
A The strong tendency of Ospreys, males especially, to return to breed in or near their birth nests is referred to as philopatry. Female Ospreys also demonstrate philopatry, but if nest sites in the area are limited, she may look elsewhere for other populations to join. By carrying different alleles or multiple variations of the same gene that will mix with the genes of her mate, she promotes genetic diversity between the populations.
Population structure arises when allele frequencies are not evenly distributed among different groups of a species. Genetic analyses of Osprey populations have revealed such allele variations between geographically distinct groups. For example, studies in the UK showed significant differences between Welsh and Scottish Osprey populations as well as between populations and outgroups from other regions.
Ursula enjoying her fish at the unused Salmon Creek nest box, courtesy of Cindy Sedlacek.
Allele frequencies differ between geographically distinct groups primarily due to factors like genetic drift, natural selection, and gene flow. Genetic drift, which is the random fluctuation of allele frequencies, is more pronounced in small, isolated populations where random events can cause allele frequencies to change significantly over time, leading to the fixation of some alleles and the loss of others. Geographic isolation limits homogenization of populations by limiting gene flow.
Natural selection is a mechanism for adaptation and evolution, where traits that enhance an organism's ability to survive and reproduce become more common in a population over generations effectively driving evolution. Selection pressures imparted by the external forces influencing Osprey populations include predation of eggs and young, competition for fish with eagles and herons, and disease. Pressures from humans include habitat destruction from pollution by pesticides, heavy metals, and microplastics as well as the collective events associated with climate change. Selection pressures favoring different alleles dictate migratory patterns, nesting behavior, and dietary habits leading to changes in the genetic makeup of a population over time.
Gene flow, the movement of alleles between populations, can homogenize allele frequencies especially if there is a high rate of migration. However, if gene flow is limited by geographical barriers or differences in mating preferences, then regions can develop distinct allele frequencies.
Orpheus in air with Ursula on the nest looking into the nest cam (right), courtesy of Cindy Sedlacek.
Osprey populations display evidence of overt diversities in their genetic makeup, geographical distribution, migratory patterns, nesting behavior, and dietary habits. This diversity reflects the adaptability of the species to various environments and ecological conditions.
Ospreys exhibit relatively high genetic diversity, which has been demonstrated using molecular markers like mitochondrial DNA and microsatellites. While there are distinct genetic groups representing geographic regions, low variability is observed within each group, suggesting a degree of genetic isolation. The high genetic diversity allows Ospreys to tolerate limited inbreeding that results from returning to natal sites to breed.
Eyes to the sky!
Candace
Candace E. Cornell
Salt Point Natural Area
Cayuga Lake Osprey Network
Guest photographer: Ithaca’s Cynthia Sedlacek brilliantly captures the Ospreys of Cayuga Lake with the intimacy of a true bird lover. Enamored by the animal’s gorgeous wings and graceful flight, her work is a tribute to the power and grace of these stunning raptors.
EYES ON OSPREYS
WATCH!
Salt Point Osprey Cam 2025 LIVE! authenticated
Salt Point Osprey Nest Cam 2019-23
READ!
VISIT!
Cayuga Lake Osprey Trail Nests Driving Tour
Complete Cayuga Lake Osprey Trail
HELP PROTECT OSPREYS:
• Stay 100-300 feet away from Osprey nests during the breeding season.
If the Osprey vocalizes or flies off the nest you are too close!
BACK OFF IMMEDIATELY.
• Carry binoculars to view wildlife from afar.
• Dispose of used fishing lines, twine, nets, and plastics which
can kill Ospreys and other animals of the lakeshore.
• Join the Cayuga Osprey Network: cec222@gmail.com.
• Find an injured animal? Call the Swanson Center at 607-253-3060.
The Janet L. Swanson Wildlife Health Center, an annex of the Cornell University Hospital for Animals, is a veterinary hospital dedicated solely to the treatment of ill or injured native wild animals. They provide expert medical and surgical care for over 1,000 patients annually, from locally and across the state of New York, with the goal of releasing them back to the wild. The Wildlife Health Center operates within Cornell University, a registered nonprofit, and relies largely on public donations.
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