An Exceptional Nesting Season

Good news about the natural world doesn’t come every day. Fortunately, we have some springtime cheer to pass around. The wading bird nesting season in South Florida was exceptional in 2021. This flighted fauna produced nearly 102,000 nests, making it the second-largest nesting effort since surveys began in the mid-90s. Happily, due to ideal conditions, many of these nests also produced fledglings. 

South Florida is the most important breeding area for wading birds in North America, so keeping tabs on nesting here is critical. As top predators, wading birds reflect the health and viability of the Everglades, a vast set of wetlands, forests, and other ecosystem types covering the bottom half of the state. Wading birds are also some of our most charismatic residents, delighting the seasoned bird watcher and novice alike.

The counts from the 2021 season, stretching from December 2020 to July 2021, come out a year later because it takes some time to compile and analyze the data. The South Florida Water Management District, working with numerous scientists across the Everglades, produces an annual Wading Bird Report. This yearly checkup reveals important insights into the world of wading birds and the health of their habitat, the Everglades.

Highlights from the Season 

Last year, much of the season’s improvement came from white ibises, the most abundant wading bird in South Florida. With over 68,000 nests, they produced nearly 2.5 times their decadal average. Other species also had an exceptional nesting season. For instance, the numbers of great egret and roseate spoonbill nests were the second largest in recent decades. Wood storks, a federally threatened species, also produced an above-average number of nests.

Checking in on some of our smaller species, such as snowy egrets, little blue herons, and tricolored herons, the news becomes less festive. While this charming set of species nested in above-average numbers (from ~1000 to >4,400 nests), these levels were well below historic nesting numbers of 10,000 nests. This is concerning because these species have undergone sharp declines in recent years in South Florida. The causes behind this are unknown, but conditions limiting the availability of food may play a role.

Wading through Water: The Importance of Wetlands

Wading birds’ nesting success isn’t a stroke of luck; rather, it depends the health of the wetlands they inhabit. These species are highly attuned to water levels, especially when they’re breeding in the dry season (from November to April in Florida). During this time, water depths that fall to low levels without rising again will concentrate dispersed prey in deeper areas of the landscape. However, if this doesn’t happen, it makes it difficult for them to capture enough prey fish and crayfish to feed their rapidly growing chicks. During the wet season (from May to October), when water levels rise, these prey items disperse into shallower marshes to reproduce and avoid predation. Unfortunately, a lack of abundant food can lead to nest failure and abandonment.

Last year, conditions leading up to the breeding season were ideal. The previous wet season had record-breaking rainfall resulting in long periods of flooding across extended areas. This increased populations of prime wading bird food, fish and crayfish. Then, during the breeding season itself, water levels dropped slowly, providing optimal foraging conditions. These environmental conditions resemble those in 2018, which had a banner nesting season with over 138,000 nests. With the highest count since the mid-90s, it was an (exceedingly) exceptional nesting season!

Shifts in the Nurseries

Times are changing, and wading birds are no exception. In South Florida, they’ve shifted and altered their schedules in response to changes in their environment. For starters, the majority of wading birds used to nest in the coastal Everglades, likely since it offered a smorgasbord of food. Recently though, they’ve shifted inland in Florida or moved to other southeastern states to breed. Reduced freshwater flows into coastal areas has lowered prey availability and likely caused this shift. One goal of Everglades restoration is to have half of wading birds nesting in this region. While only 34% of wading birds nested in this region this year, this was one of the highest numbers recorded in recent decades.

Another notable change is that wood storks are starting their breeding season later in the year (from January to March). Historically, they started breeding in November or December. A shorter breeding season is problematic because chicks needs both sufficient time and food to fledge before the wet season starts in May and water levels rise. Last year, they still started moderately early (mid- to late-January). Before the breeding season, extended flooding of a particular type of inland wetlands, marl prairie, along with coastal wetlands supported wood stork foraging and may have pushed the start forward.

Baby Boom or Bust? 

Fluctuations in nest numbers from year to year are a natural part of the cycle in the Everglades. What is different now is that banner seasons, like last year’s, are not occurring as frequently or reaching the same levels as in the past. Unfortunately, wading birds have already declined by up to 90% since the 1930s and 1940s in South Florida. And they face a number of threats, including multiple changes from global warming. 

However, as this recent checkup shows, all hope is not lost. Wading bird populations have shown remarkable resilience, responding rapidly to changes in environmental conditions. Restoration of natural flows and patterns of water through the Everglades should boost wading bird reproduction. Improved conditions are also predicted to shift the timing of breeding and increase breeding in coastal areas. With Everglades restoration projects ongoing, let’s hope that another exceptional nesting season is on the way!

Want to learn more about Wading Bird Breeding?

Read the South Florida Water Management District’s annual report on the wading bird breeding season.

Check out my colleague and photographer extraordinaire, Dr. Mark Cook’s photographs here or on Instagram. 

Florida Audubon also summarizes the wading bird breeding season here.

link!!

This is a very useful guide for Florida’s birds.