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This video is proudly brought to you by the Wildlife Diversity Program at the Texas Parks
and Wildlife Department.
Texas is a major route for migratory birds and serves as a breeding site for egrets and
herons. During nesting season, most egrets and herons gather in large colonies to nest.
This nesting site is called a rookery. Rookeries can be dozens or even hundreds of nesting
birds in a concentrated area and can include 2-5 species of egrets and herons. The cattle
egret, little blue heron, snowy egret, great egret, and yellow crowned night herons are
the most common species found in a rookery. In Texas, Cattle egrets are typically the
most abundant species.
Different species arrive, nest and leave at various times throughout the nesting season.
Depending on the species, the nesting season occurs from early March to late October. On
average, egrets and herons lay 2-4 eggs and return to the same rookery each year to nest.
The preferred habitat for nesting egrets and herons is a stand of mature trees, primarily
oaks; with at least 75% closed canopy with overlapping branches. This allows the birds
to easily walk among the branches from tree to tree. Most rookeries are located near water
where there is plenty of food available for them to eat, but rookeries can easily exist
away from water in urban areas.
When egrets and herons establish rookeries in urban settings, it can become a challenging
issue. Urban rookeries can cause concern due to noise, odor, and possible health hazards.
It is not uncommon to find regurgitated fish, large amounts of feces and even deceased birds
at the rookery site. Egrets and herons can die as a result of injury, from heat exhaustion
or natural causes.
Egrets and herons are protected by state and federal laws. Under the Migratory Bird Treaty
Act, it is illegal to kill or harass the birds in any way that would cause nest abandonment
or the death of eggs or hatchlings. Nesting starts when the first egg is laid in the nest.
Up to that point, it is legal to harass or scare the birds to deter them from an area
where a rookery is not desirable. Once the first bird lays an egg, all harassment and
scare techniques must stop.
The best way to prevent the establishment of an urban rookery is through public awareness
and early detection. When birds first arrive in the spring, they are somewhat nervous and
more easily scared away. Scaring devices can be used to deter the birds. However, these
techniques cannot injure or kill the birds. In the winter months, habitat modification
by creating openings within the canopy and removing overlapping branches makes the area
less desirable for the birds.
A rookery can be an excellent opportunity for wildlife enthusiasts to observe nesting
activity, but it can become a challenging issue in an urban setting. The Texas Parks
and Wildlife urban wildlife program provides assistance to municipalities dealing with
urban rookeries.