Every year, the Northern Virginia Conservation Trust (NVCT) teams up with Stafford County and the Virginia Department of Conservation and Recreation to assess the health of the breeding ground and count great blue heron nests in Crow’s Nest Natural Area Preserve. In 2018, NVCT donated a parcel of land we protected to Crow’s Nest Natural Area preserve; this parcel is known as the Potomac Creek Heronry because it is a popular nesting spot for great blue herons! Our connection to these herons is why we love participating in the yearly heron nest count. This event is vital to their long-term protection and great fun for NVCT and partners alike! Great blue herons are the most widespread heron in North America, and the International Union for Conservation of Nature states that great blue heron populations are increasing, so why keep up the effort if heron populations across the United States are thriving?
Great blue herons are incredibly important to their ecosystems, and their absence from the places they inhabit can lead to widespread disruption. Great blue herons can be found year-round in Virginia and are the largest herons in North America. They live in various freshwater and marine water habitats, such as coasts, marshes, riverbanks, and wooded swamps. They provide the typical ecosystem services like nutrients through their excrement and being food for other animals. However, they play a more significant role as a keystone species. Keystone species are organisms that maintain the structure and function of the ecosystem due to their strong interactions with multiple species in an environment and the inability of other species to fill their role in the ecosystem. Great blue herons are at the top of their food chain; they hunt alone and feed on a wide range of animals. They typically hunt fish but have been seen feeding on other small animals like reptiles, insects, rodents, small birds, and amphibians. Raptors, such as golden eagles and great-horned owls, are the only animals that occasionally predate on them.
Being at the top of the food chain means these herons keep populations at food chain levels in check. Predating on fish, amphibians, and other small animals ensures they aren’t overpopulated, which in turn could lead to overharvesting resources like vegetation. Their predation on various species also maintains biodiversity, as no singular species is singled out as the heron’s sole food source. These herons are not easily replaced either, as other predators like raptors do not have as wide a range of diet, population numbers, or habitat preferences.
Great blue herons are also ecological indicators; their health indicates the ecosystem's health. A study completed by the Ohio Cooperative Wildlife Research Unit and Ohio State University identified great blue herons as indicator species because they are long-lived (average lifespan of 15 years), large enough for adequate tissue sampling, readily available because of their widespread stable distribution throughout the US, and their placement in the food chain. Because great blue herons are at the top of their food chain, they accumulate any contaminants their prey acquire from the environment. Scientists can look for toxins in heron tissue samples and determine what contaminants have been invading the ecosystem. Their preference for wetland habitats means they are instrumental in determining water quality, sometimes even for water we drink. While great blue herons haven’t faced conservation threats since the early 19th and 20th centuries due to hunting for their iconic blue and gray feathers, it is essential to keep up conservation efforts. While these birds are no longer heavily hunted, individual populations across North America face development threats and are affected by climate change. Spring heat waves can be too hot for heron chicks, and wildfires threaten to destroy their habitats. Consistent conservation practices ensure these beautiful birds’ population numbers don’t dwindle, creating widespread unbalance in the ecosystems they inhabit.
Nest counts are one way to monitor the growth of a population over time and determine that the nesting area is intact. Herons nest in “rookeries,” which are colonies of breeding birds. They like to nest in tall trees away from human disturbance and have access to wetlands they use as feeding areas. Several nests can often be found in a singular tree. In Virginia, the trees they prefer are loblolly pine and sycamore trees. Males choose nest sites and court-passing females. Nests are built of sticks and small twigs; males gather the materials, and females craft the nest.
Our group splits into two to survey polygons that capture trees that have hosted heron nests for the past three years. Colonies can shift around due to tree mortality or simply because of a preference change. Trees with nests are tagged, and each group seeks out these tagged trees to check how many nests are present, if any. This year, we counted 201 nests, which is not far off fromsimilar to last year’s total of 211. We had one new sycamore tree that had three nests in it and two other sycamores with nests that had previously not hosted nests since 2009. The overall trend for heron nests has remained stable for the last few years, with an average of 211 nests since 2020.
The fact that the nest numbers have remained stable over the years indicates that everyone involved is doing their job right! Nesting herons can be especially sensitive to disturbances like human activity and noises from nearby traffic, so living on a preserve guarantees they have enough buffer space between them and human civilization. NVCT, and the Virginia Department of Conservation and Recreation manage and steward the land these herons live on with support from Stafford County, meaning that the habitat is not only forever protected, but the land is consistently cared for. These herons and the many other species that reside in the Potomac Creek Heronry have all the resources they need to thrive. NVCT looks forward to many more heron counts in the future because we are committed to saving nearby nature that sustains the ecosystems of Northern Virginia and adds to its wildlife and wonder.
Comments