Breeding Ecology of the Little Blue Heron on the West Coast of Florida

Abstract

-Little Blue Herons (Florida caerulea) nest most often in association with the Schinus-Sabal community on the Alafia Banks, Florida. The number of active nests reaches two peaks during the breeding cycle; breeding time seems unaffected by cooler temperatures in the winter or spring. Peaks probably result from two different breeding populations and not from renesting. Mean clutch size is 2.91 + 0.09, hatching success is 92.1%, and nestling survivorship to two weeks of age is 53.0%. Egg loss and nestling mortality can be attributed to nestling starvation, nest collapse and predation. Little Blue Herons on the Alafia Banks lay smaller clutches and fledge fewer young compared to most populations studied in other areas. The Little Blue Heron (Florida caerulea) is listed as a of special concern in Florida (Kale 1978), and it has also declined elsewhere in most of its range (Ogden 1978). The main reason for this situation appears to be drainage of wetlands but the mechanism can only be learned from studying breeding success and ecological requirements of the species in a variety of habitats. The breeding ecology of Little Blue Herons has mostly been studied in freshwater habitats (Meanley 1955, Jenni 1969, Summerour 1971, Werschkul 1977, Wiese 1977); few data are available from the coast (e.g. Maxwell and Kale 1977). I report here on the breeding success and nesting ecology of this species on a dredged-material island off the west coast of Florida. STUDY AREA AND METHODS I conducted field studies from 1976 to 1978 on the Alafia Banks, Hillsborough Bay, Hillsborough County, Florida. The Alafia Banks consist of two dredged-material islands (Bird and Sunken islands) where Little Blue Herons breed most often in Brazilian pepper (Schinus terebinthifolius), cabbage palm (Sabal palmetto) and black mangrove (Avicennia germinans). These herons also nest in red mangrove (Rhizophora mangle) on Bird Island, but this population was not studied. Within the regions used by Little Blue Herons on the Alafia Banks, 125 pairs of Snowy Egrets (Egretta thula), 175 pairs of Louisiana Herons (Hydranassa tricolor), 75 pairs of Black-crowned Night Herons (Nycticorax nycticorax), 75 pairs of Yellow-crowned Night Herons (N. violacea), 75 pairs of Glossy Ibis (Plegadis falcinellus) and 4,500 pairs of White Ibis (Eudocimus albus) also nested. Bird and Sunken islands were created in 1931 and 1961, respectively, and differ in their geology, bird populations, and flora. Data for the relative frequency of plants in the study area (Table 1) were derived from Lewis and Lewis (1978). The history and habitat of the Alafia Banks have been described by Schreiber and Schreiber (1978) and Lewis and Lewis (1978). Nestling Little Blue Herons were banded with U.S.F.W.S. aluminum bands and with individually numbered, colored leg-streamers to aid in identification. Nests were marked and data collected twice weekly on nest failure, clutch size and nestling survivorship. Nests were checked during early daylight hours from March to August of each year. Nests and eggs of Little Blue Herons were indistinguishable from those of other intermediate sized day-herons, but nests were identified by observing their adult and/or nestling occupants.