Report: Wading bird nest totals rise, but concerns remain



Wading birds in South Florida built or started 101,794 nests during the 2021 nesting season, according to an annual census of the region’s herons, egrets, ibises, spoonbills, and other waders.

It was the second largest annual nesting effort observed since comprehensive system-wide surveys began in South Florida in 1996. The total nest count is comparable with the historical large nesting events that occurred in the 1930s and ‘40s. It is over double the 10-year average (48,328.8 nests) and second only to the banner nesting season of 2018, when an estimated 138,834 wading bird nests were produced in South Florida.

Most wading bird species exhibited increased nesting effort during 2021. Of note was the large number of nests produced by the White Ibis (68,335 nests), which was almost 2.5 times the 10-year average (28,200.6 nests). The federally threatened Wood Stork produced 3,916 nests, which was 52% more than the 10-year average (2,552.0 nests). Roseate Spoonbills produced 1,219 nests in South Florida, which was almost double the 10-year average (614.6 nests) and the Great Egret produced 15,306 nests in 2021, which was 1.7 times the 10-year average (8,766.4 nests). Even the small herons of the Egretta genus (Snowy Egret and Tricolored Heron), which have shown sharp declines in nest numbers over the past decade, showed a moderate improvement in nesting effort in 2021; for example, the state-listed Snowy Egret produced 4,426 nests, 55% more than the 10-year average.

More nests in Everglades coastal areas

The Everglades Protection Area (including the Water Conservation Areas and Everglades National Park) supports most of the nests in South Florida and produced 89,514 nests (88% of all nests in South Florida) during 2021. The next most important nesting area is Lake Okeechobee. This year, the lake produced an estimated 3,793 nests, slightly less than the 10-year average (4,207.3 nests), and only 3.7% of the nests in South Florida. 

In the Everglades, the coastal region of Everglades National Park historically supported approximately 90% of all nesting wading birds in the Everglades, probably because it was the most productive region of the Everglades ecosystem. During the past 80 years, productivity in this region has declined due to reduced freshwater flows to the coast and nearby marshes, and the location of nesting has shifted to inland colonies in the Water Conservation Areas. In 2021, however, the proportion of nests in the coastal region (34%) was one of the highest recorded in recent decades and continues a trend of increased nesting in this area. While this proportion remains short of the 50% restoration target, the magnitude of nesting (approximately 29,918 nests) was considerably higher than it has been in recent years.

Tens of thousands of young birds

Nesting success in the Everglades during 2021 was relatively high for all indicator species of the Comprehensive Everglades Restoration Plan, with between 58% and 88% of focal study nests fledging at least one offspring. Overall, tens of thousands of young birds were produced, which will help boost population levels for future nesting years. 

The successful nesting during 2021 highlights the critical role of hydrology and its corresponding effects on wading bird prey (fish and crayfish) availability and nesting responses. In short, wading birds require relatively deep conditions across the landscape prior to the nesting season to promote the production of aquatic prey animals, followed by a relatively dry winter nesting-season that reduces water levels and increases the accessibility and vulnerability of those prey to birds during nesting. Conditions leading into the 2021 nesting season were characterized by exceptionally high rainfall, long hydroperiods, and a large spatial extent of flooded habitat, which extended prey production across the Everglades landscape. November 2020 through early June 2021 was characterized by a continuous drop in water level across the Everglades landscape that led to exceptional foraging conditions at the right time and place throughout much of the ecosystem. Foraging conditions were further enhanced by several recently completed restoration projects that promote the flow of freshwater to the southern Everglades and Florida Bay. 

Some birds sharply declining, causes unknown

Historical nesting data from the pre-drainage Everglades reveal that nest numbers naturally fluctuate considerably among years in accordance with hydrologic conditions. A single year of nesting data is therefore insufficient to understand the health of the Everglades or its populations of nesting wading birds, and instead we need to consider long-term nesting patterns. The long-term data provided by this annual wading bird report reveal that several nesting responses have improved in the Everglades over the past 20 years, but some measures are not improving.

The report’s authors, Mark Cook and Michael Baranski, of the South Florida Water Management District, note that the overall numbers of Snowy Egret, Tricolored Heron, and Little Blue Heron “have been sharply declining, and the causes of the declines are unknown.” They also report that despite improved nesting effort for Wood Storks, “the late timing of their nesting (with the exception of a few recent years) has remained relatively static, and their nesting success often is below that necessary to sustain the regional population. The ratio of tactile (Wood Stork, White Ibis, and Roseate Spoonbill) to visual (herons and egrets) foragers has improved since the mid-2000s but remains an order of magnitude below the restoration target.”

This year is the 27th edition of this multiagency annual report. It continues to be an essential resource for guiding Everglades restoration strategies and weekly operational decisions.

Thanks to the South Florida Water Management District for providing this news.

2020 Everglades breeding season mixed for wading birds

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