Movement Patterns of Wading Birds as a Mechanism Linking Freshwater Wetlands and Coastal Ecosystems in the Greater Everglades

The large-scale Comprehensive Everglades Restoration Plan (CERP) aims to reduce ecological impacts to coastal areas of South Florida by increasing the amount of freshwater flow to these systems. The sensitivity of wading birds to hydrologic conditions is the basis for that group of species being selected as prominent indicators of restoration progress, with species-specific predictions of their responses (Frederick et al. 2009).

Nevertheless, mounting pressures external to CERP, such as sea level rise and coastal development, could confound predictions of wading bird response to restoration. Baseline sea level change since 1913 in Key West is now 2.4 mm/year (NOAA 2019). This increase threatens to drastically alter the timing and areal extent of feeding habitat for wading birds and other species whose reproductive cycle is inextricably linked to natural hydrologic fluctuations, regardless of the effects of CERP. Additionally, the degree to which wading birds nesting in coastal areas depend on freshwater habitat for some part of their annual cycle is unknown.

One way to disentangle the predicted effects of CERP from external factors is to test for differences in movement patterns and selection of resources by individual wading birds both within and outside the footprint of CERP. This study proposes to use satellite transmitters and output from the Tidal Model of Shallow Water Availability (TiMSA; Calle et al. 2016) to quantify and contrast the daily movements and resource use patterns of Little Blue Herons (Egretta caerulea) that forage in the Florida Bay and the lower Keys archipelago.

Project Goals and Objectives

1. Contrast the annual movement patterns of Little Blue Herons in an estuary and archipelago with an emphasis on the linkage between colony sites and foraging habitat. Specific objectives under this goal are to:

• Determine the nesting location for birds that leave the tidal flats prior to breeding and for those that remain on the tidal flats.
• Contrast between study areas the degree of colony and foraging site fidelity and seasonal movement patterns of birds including the identification of core foraging habitat.

2. Quantify the annual cycle of habitat selection by Little Blue Herons in an estuary and archipelago. Specific objectives under this goal are to:

• Develop a resource selection function model (RSF) utilizing the hydrologic model TiMSA (Calle et al. 2018) and other relevant habitat variables.
• Contrast differences in RSFs between study areas.
• Contrast between study areas the degree to which birds that forage on tidal flats utilize freshwater habitat.