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How do you define a species? Seaside Sparrow population genetics told through photography
By Eric Fortman
Tahiti Beach, St. Vincent National Wildlife Refuge. Our field sites dotted the northern half of Florida, from Port Richey, to Jacksonville, and across to Pensacola.
It’s summer time and that means it’s nesting season for all kinds of creatures. For the past two summers I’ve had the pleasure of working on a seaside sparrow genetics project with Carolyn Enloe, a University of Florida graduate student.
Seaside sparrows inhabit salt marshes along the Eastern Seaboard and Gulf of Mexico. Unfortunately, humans like to inhabit coastal marshes as well. So habitat destruction from development, has impacted many populations. Unlike their northern relatives, Florida’s resident seaside sparrows typically don’t travel more than a 10km radius from the nest where they were born. Because of this high site fidelity and their specific habitat requirements, the species has suffered from habitat fragmentation. Currently the species exist in several disjunct populations spread around the state. There are four currently recognized extant subspecies of seaside sparrow in Florida: MacGillivray’s (Ammodramus maritimus macgillivraii), Scott’s (A. maritimus peninsulae), Louisiana (A. maritimus fisheri), Wakulla (A. maritimus juncicola), and Cape Sable (A. maritimus mirabilis). The goal of the project is to better understand how these subspecies and subpopulations are related to each other. The three aspects used in the study are: genetics, plumage coloration, and song.
Julia Magill records a seaside sparrow song. Much like humans have different dialects, birds can too. Differences in bird songs can give us clues about how different populations are related.One of the challenges of studying these cryptic marsh birds is their preference to spend most of their day hiding among the marsh plants. Usually the only times we see them is when they are singing for a mate, and during their brief flights between patches of marsh grass.Even their nests are just a few inches above the ground. This one was carefully camouflaged with saltgrass.A field Technician carefully untangles a sparrow from a mist net.After capture, each bird gets sized and fitted with an aluminum leg band.The leg bands are issued by the North American Banding Program through the US Geological Survey. These light weight aluminum bands are stamped with a unique number. This way if another researcher captures the same bird, the data points can be linked together to reveal details of its life history.Julia Magill shows Doris Duke intern Hanna Innocent how to take a tarsus measurement on the sparrow. Body measurements -or morphometrics- allow us to compare the proportions on the birds and look for patterns between populations.Carolyn Enloe shows Doris Duke intern Jeanelle Brisbane where to draw blood from the sparrow. DNA is extracted from the blood samples to compare differences between populations.To keep photos clean and consistent we had to develop a standardized protocol for photographing sparrows.Our photo studio in the marsh at Adams Beach. The photo tent helps keep the quality of light consistent between locations.To compare feather coloration between individuals, each bird was photographed in six different poses. Because the color of sunlight is different in the morning than it is at mid day, a color checker was used to ensure consistency between samples.After being processed, each bird was carefully released back into the wild.
Eric Fortman is a hobo biologist and photographer, presently living in South Florida. He is currently pursuing an M.S. in Biology, studying the microbiome of Biscayne Bay. To see more of his work visit EricFortman.com or Instagram: @EricFortman.
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