Food Habits

Main Foods Taken

Primarily small fish; oft-repeated listing of frogs and tadpoles (based on Cahn 1923) either exceptional or incorrect.

Microhabitat For Foraging

Typically forages singly on broad open flats 5–15 cm deep, rarely to about 25 cm; key characteristics include barren sand or mud substrate with limited vegetation, or storm events that cause overwash deltas on back sides of barrier islands (as is true especially for Texas). Algal mat commonly present in mainland lagoons, keys, and salt barrens of Florida; also forages on sparsely vegetated mangrove flats among seedlings. This species often exploits seasonal drydown conditions that trap prey in draining pools or creeks and may join mixed-species foraging flocks including other herons, pelicans (Pelecanus spp.), ibis (Plegadis spp.), Roseate Spoonbill (Ajaia ajaja), and Least Tern (Sterna antillarum).

Food Capture And Consumption

Visual, day feeder. Most varied and active of any North American heron in foraging techniques used; most methods variation of Disturb and Chase (Meyerriecks 1960: 107). Prey is grasped, tossed to back of throat, and swallowed quickly. Occasional large prey >10 cm in length (e.g., needlefish [Strongylura sp.] or mullet [Mugil sp.]) require more handling time. Capture rate (percentage success of total strikes) 32% for adults and 25% for immatures in Tampa Bay in Florida (Rodgers 1983); 42% for adults and 29% for immatures in Texas (RTP).

Feeding behavior nomenclature and description based on Meyerriecks 1960 .

Wing-Flicking. This distinctive method of foraging quite common and characteristic of this species. Individual moves forward slowly while partly extending and retracting wings rapidly; “ . . . a lurching, weaving type of half-run, half-jump progression. As the bird reels forward, it stabs rapidly to the right and left, attempting to seize any prey disturbed by its activities. This method is used primarily in very shallow [author’s emphasis] water” (Meyerriecks 1960: 108).

Open Wing–Feeding. Also characteristic of this species. Similar to Wing-Flicking but with wings partly extended.

Canopy-Feeding. Individual runs forward with wings extended, halts and peers into water and brings both wings forward over its head, forming a canopy over head and neck, this pose held for few moments to several minutes; shadow produced by wings apparently attracts fish.

Foot-Stirring. Individual wades slowly and vibrates its feet over mud surface, imparting a scraping motion to the feet; then stops and peers at water surface.

Hovering-Stirring. Aerial variant of typical stirring or scraping; individual moves slowly forward, then suddenly launches into flight, hovers over water surface and, in flight, gracefully scrapes mud or aquatic vegetation with one foot; strikes made from hovering (see also Meyerriecks 1959).

Stand and Wait and Wade or Walk Slowly. Stationary foraging rather infrequently employed. Variant of Walk Slowly termed “head-tilting,” in which individual moves rather slowly through the water with its head and neck strongly inclined to one side as it peers intently at surface; holds head and neck tilted to one side throughout any chases of prey.

Major Food Items

Small (mean mass about 1 g) fish.

Quantitative Analysis

Few quantitative studies, all based on nestling regurgitations. McMurry (1971) and Simersky (1971) identified 96 fish from 14 boluses collected from a Laguna Madre, TX, colony: sheepshead minnow (Cyprinodon variegatus; 83%), longnose killifish (Fundulus similis; 9%), pinfish (Lagodon rhomboides; 5%); also striped mullet (Mugil cephalus) and ladyfish (Elops saurus).

From regurgitated pellets collected from nestlings in Aransas Bay, TX (n > 1,500), most abundant were sheepshead minnow (69.6%), mullet (Mugil curema, M. cephalus; 10.6%), pinfish (5.4%), longnose killifish (4.3%), and tidewater silverside (Menidia peninsulae; 3.3%); also 11 other fish species, 1 shrimp (Penaeus aztecus), and 1 crab; mean mass of items 1.3 g; mass of sheepshead minnows averaged 0.74 g. From regurgitated pellets from nestlings in Florida Bay, FL (n > 5,100), most abundant were sheepshead minnow (53.6%), sailfin molly (Poecilia latipinna; 13.5%), goldspotted killifish (Floridichthys carpio; 10.6%), and marsh killifish (Fundulus confluentus; 8.3%); also 28 other fish species, 1 shrimp (Penaeus duorarum), and 2 insects; mean mass of items 1.1 g; mass of sheepshead minnows averaged 0.6g (Paul 1991, 1996; RTP).

No information on food selection. Not known to store food.

No information.

No laboratory studies. Adults and nestlings perform gular-flutter to maintain evaporative cooling in hot conditions. By age of about 1 wk, nestlings also seek shade, if available. Adults, subadults, and fledged immatures hunch and fluff feathers in cold weather (RTP).

Foraging adults drink brackish or salty water while foraging. No pellet-casting known, but adults regurgitate compressed boluses of fish to nestlings and both adults and nestlings may regurgitate when nest threatened. Nestlings defecate into nest or over lip; adults defecate while standing, flying, or preparing to fly. Foraging birds commonly leave water to defecate (RTP).