Higher Trophic Levels

Roseate Spoonbill Populations in Florida Bay

Florida Bay Project Profile - 64

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Question: What factors are responsible for the trends observed in Roseate Spoonbill populations?

Project: Roseate Spoonbills (Ajaia ajaja) are listed as a species of special concern in the state of Florida. Ninety percent of the state's breeding population nests on mangrove islands in Florida Bay. During the last half of the 1800's and through the early 1900's, wading birds were hunted for their elegant breeding plumes which were used to decorate the ladies hats in fashion at the time. Hunting took place during the breeding and nesting season which disrupted the nesting colonies and affected offspring survival. Spoonbills were heavily impacted by these activities. Although federal legislation protected wading birds, continued human predation on adults and eggs had probably eliminated all spoonbill colonies except the Bottle Key colony which had been reduced to fifteen breeding pairs in 1935. In 1947, the creation of Everglades National Park protected spoonbills from further human disturbance. Nest numbers began to increase, with the majority of spoonbills nesting on mangrove islands in the southeastern and southwestern subregions of Florida Bay. Today, however, the majority of birds nest in the northwest region of Florida Bay and overall declines in population numbers have been noted for the species.

Using the information that has been collected over the last fifty years, this project examined the four major factors that could potentially explain the shifts of breeding colonies from one subregion to another and explain the recent overall declines in population numbers. The factors examined were: parasites and disease, predation on nests by raccoons, direct human disturbance (hunting, general colony disruption) and availability and quantity of food resources.

Findings: Quality and availability of food resources is an important factor determining spoonbill nesting success. Starting in the early 1960's, spoonbill nest numbers increased in the northeastern subregion of the bay. This increase coincided with the abandonment of colonies in the southeastern and southwestern bay. Nest abandonment probably occurred because dredge and fill operations altered the many acres of wetlands on the mainline Florida Keys which served as feeding grounds for spoonbills and their chicks. In the northeast, where most of the nests were located between 1960 and 1990, the mainland wetlands associated with the southern Everglades, northeastern Florida Bay and southwestern Biscayne Bay served as the primary feeding grounds. However, in the mid 1980's the number of nests in the northeast began to decline. The 1999 nesting survey indicated the lowest number of nests in the northeastern subregion since 1967; and for the first time the majority of spoonbill nests were located in the northwestern subregion of Florida Bay. Spoonbills nesting on islands in the northwestern part of Florida Bay feed primarily on Cape Sable.

An examination of the fifty year record shows that the wetlands in the northeast were subjected to three distinct periods of water management practices. During Period I (19501963) the impact of water management on the wetlands was relatively small. Period II (19631982) was characterized by the construction and operation of the C111 and associated canals. During these first two periods, spoonbills had high nesting success and showed an overall increase in nest numbers. However, spoonbill nest success was low and the number of nests declined sharply in Period III (19831999), which was characterized by the completion and operation of the South Dade Conveyance System. These findings suggest that current water management practices in the southern Everglades may have degraded the coastal wetlands in northeastern Florida Bay making them unsuitable as spoonbill foraging grounds. Changes in wetland characteristics may have altered the food supply which may account for the overall decline in nest numbers and the most recent shift of the spoonbills to the northwest bay.

Status: This study was completed in 1999. Biologists will continue to monitor spoonbill populations.

Restoration Impacts: These data suggest that nesting Roseate Spoonbills show a measurable response to water management practices in the southeastern Everglades and respond in a predictable manner. Because spoonbill population levels are tied to water management practices, they may be considered a good indicator species for the restoration of the Everglades/Florida Bay watershed.

Funding Source: Everglades National Park

 

Related Profiles:

FBPP 59

fbpp 63