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Main Foods Taken
Microhabitat For Foraging
Typically open, shallow-water sites (fresh, brackish, salt, hypersaline) with small aquatic animals (Allen 1942, Hancock et al. 1992). In Florida Bay, primarily mangrove estuary of mainland bordering bay (red mangrove [Rhizophora mangle] and spike rush [Eleocharis cellulosa]) and adjacent freshwater Everglades (wet marl prairie; Bjork and Powell 1994). Found primarily in dwarf open mangrove, in open shallow pools and interconnected channels of water created by patches of mangrove trees, and in vegetated creeks draining mangrove and prairie (3,225 birds, 30% each category, n = 9 aerial surveys, Nov–Mar 1990–1991; Bjork and Powell 1994). Sensitive to changes in water level; as dry season advances, moves to deeper creeks and moats around tree islands (hammocks); shifts from mangrove estuary north to freshwater prairie (Bjork and Powell 1994). Less typically, forages in shallow sea grass–covered banks of Florida Bay (Powell 1987). In Water Conservation Areas of Everglades, often found roosting in or feeding near willow (Salix sp.) islands (Bancroft and Sawicki 1992). In Tampa Bay area, forages primarily in mouths of tidal creeks, roadside ditches and ponds, and Hillsborough River drainage (R. Paul pers. comm.). At Kennedy Space Center, uses open areas of mosquito control impoundments (Smith and Breininger 1995). In Texas, uses shallow areas of bays that can become reduced to landlocked ponds or puddles as a result of evaporation; associated vegetation dominated by salt grass (Distichlis sp.), the grass Monanthochloe littoralis, sea oxeye (Borrichia sp.), and saltwort (Batis maritima, San Antonio Bay; Allen 1942).
Depths of ≤12 cm typical (H. Hobart in Lewis 1983). Maximum foraging depth of about 20 cm based on leg length of study skins (Powell 1987). However, will feed in water above chest, with entire head and neck submerged (Hancock et al. 1992). Royal and Yellow-billed spoonbills show similar feeding behavior (Vestjens 1975a). Typically active during daylight, but commonly feeds at night (Allen 1947, Friedmann and Smith 1950, Powell 1987). Feeding peaks at low tide in tidal areas (Allen 1942).
Flight distance and duration of adults tracked from 5 colony sites in n. Florida Bay to mangrove estuary: mean 12.4 km ± 5.8 SD and 19.1 min ± 12.1 SD (n = 92 birds; Powell and Bjork 1989) Adults frequently fly longer distances (30 km) from nest site to feeding areas (A. Sprunt IV and W. B. Robertson, Jr. in Lewis 1983); flight distance as great as 65 km documented (Bjork and Powell 1996). In Texas, breeding adults traveled 1–1.5 km from colony site to feed (D. H. White in Lewis 1983).
Food Capture And Consumption
Available information is mostly descriptive; no data on behavior or foraging ecology—e.g., rate of sweeping, percentage of time devoted to different feeding behaviors, capture rates. No data on how these factors, especially capture success, vary with prey abundance, dispersion (extent of drying and concentration of prey), prey type, habitat, and seasonal changes in energy demands. No information on effect of predation on prey populations (see Howard and Lowe 1984 for Royal Spoonbill).
All spoonbills use tactile and visual cues to obtain prey; characteristic feeding behavior is Walking Slowly and Head Sweeping (Allen 1942, Kushlan 1978). Head Sweeping is primarily tactile; searches for prey by scything partially open bill from side to side through water or mud while walking; when prey contacts spoon, bill clamps shut (see below). Swallows food by raising bill slightly and jerking head backward rapidly in reverse probe that throws food back toward throat (Hancock et al. 1992, JVD). Other feeding behaviors include Intensive Sweeping, Probing, Grabbing, Pecking, Groping, and Gleaning, combined with various body movements (Walking Slowly, Standing, Running, Hopping; see Vestjens 1975a, Kushlan 1978, and Hancock et al. 1992 for descriptions). Regardless of foraging method, catches all prey in spoon. Uses Probing and Intensive Sweeping to search small areas. Yellow-billed and Royal spoonbills have been observed Probing while searching around water plants or submerged logs (Vestjens 1975a). Incorporates visual cues while feeding tactually; some behaviors, such as Grabbing and Gleaning, are visual. Captive Roseates sweep heads until “seeing” a tray of cut-up fish, which they simply grab with spoon and swallow (Allen 1942). Will run after abundant active prey, when it sees them (Allen 1942). Probably stirs up mud bottom with feet when walking, flushing prey that it catches in next sweep of bill (Vestjens 1975a). Conspecifics and other species may benefit from flushed prey; see Behavior: social and interspecific behavior, below.
May handle prey in the spoon by biting (munching) as a selective and preparatory process before swallowing (Allen 1942). Also shakes large, awkward, or hard-shelled prey vigorously in bill to remove extremities, and beats them against hard surfaces to crack shells or carapaces; these actions facilitate swallowing, and perhaps digestion as well.
Mechanics of tactolocation are not well understood. Spoon of upper mandible has a small outgrowth at tip (“nail”), and a corresponding outgrowth of smaller size on lower mandible, evidently for gripping and tactolocation (Allen 1942). Both mandibles appear to be supplied with nerves that run all the way to tip and nail. Apparently, prey item must contact spoon in order to be eaten, although the spoonbill may use tactile stimulation from other portions of bill (Vestjens 1975a).
Head Sweeping appears to be innate (Kushlan 1978). Juveniles must learn how to feed efficiently, but no data on age-related capture success (Allen 1942; see also Vestjens 1975a). Head Sweeping may impose important constraints on nesting ecology, but this relationship is not well understood; for other tactile forager (Wood Stork [Mycteria americana]), see Coulter et al. 1999 .
Major Food Items
Mostly small fish, crustaceans (mostly shrimp and prawns), and aquatic insects (beetles [Coleoptera], bugs [Hemiptera]; Howell 1932, Cottam and Knappen 1939, Allen 1942, Powell and Bjork 1990, Hancock et al. 1992).
The following is based on a small sample, mostly from Florida; different collection techniques and units are used for expressing amount of food items. However, small fish (minnows, killifish) constitute most of diet (42–90%); crustaceans (mostly shrimp) make up most of remainder (5–55%; n = 30 [4 stomachs and 25 bolus samples from nestlings—all from Florida—and 1 stomach from Texas]; see below).
In Florida, 4 stomachs were taken in Feb and Mar (Cottam and Knappen 1939); 1 empty stomach contained 90% bone fragments of sheepshead minnow (Cyprinodon variegatus) and 10% wood pulp; 3 full stomachs contained 80.7% fish, 11.3% water beetles, 4.7% shrimp, 3.3% plant material, and traces of gastropods and other aquatic bugs (percentage by volume; Allen 1942). Details provided on 2 of these stomachs: A nearly grown young bird from Alligator Lake colony, FL, contained total of 246 fish (82%): 19 top minnows (Zygonectes notti, 9%), 21 killifish (Fundulus sp., 9%), 3 sheepshead minnows (2%), 4 killifish (Jordanella florida, 2%), 46 top minnows (Mollienesia latipinna, 17%), 43% fragments of top minnows and killifish (Cyprinodontidae and Poeciliidae); trace fish eggs. Also contained the following: (1) crustaceans: >152 shrimp (Palaemonetes exilipes, 9%); (2) insects: 49 predaceous diving beetles (Thermonectes basilaris, 5%), >23 fragments of water-scavenging beetles (Tropisternus glaber, 2%) and trace of other arthropods, a snail, and plant material. Stomach of adult from Cape Stable, FL, contained small fishes (42%), 3 sedge tubers (Cyperus sp., 42%), and 1 crustacean (16%).
In Florida Bay, 25 boluses were collected and their contents analyzed in terms of percentage wet weight (Powell and Bjork 1989, 1990): In 6 nestlings, 85% small fish (50.8% fish parts, 3.6% sheepshead minnow, 28.8% marsh killifish [Fundulus confluentus], 1.4% sunfish [Lepomis sp.]) and 15% small shrimp (Palaemonetes sp.); in 19 nestlings, about 90% small fish (about 75% unidentified fish parts, fish scales, bones, partially digested tissue, and inorganic material [marl]; primary fish species sailfin molly [Poecilia latipinna], also marsh killifish and sheepshead minnow) and 10% palaemonid shrimp.
In 1 Texas stomach collected in a freshwater cattle pond (Allen 1942), 55% crustaceans by volume (5 shrimp [Peneus sp.] and 5 prawns [Palaemonetes sp.], 1 small crayfish, 1 isopod); 31% insects (60 back swimmers [Notonecta sp.], 10 water boatmen [Corixidae]); 14% fish (1 small pinfish [Lagodon rhomboide], 16 immature top minnows [Gambusia patruelis]); gastropod trace (slug). All items were <30 mm, most <20, in length.
Food Selection And Storage
Preliminary results in Florida Bay suggest that nestlings are fed the most abundant fish species available (sheepshead minnow, marsh killifish, sailfin molly) with little prey selection (Powell and Bjork 1990). Royal Spoonbills forage selectively in sea grass beds, ingesting mostly large adult female shrimp relative to abundance in field (Howard and Lowe 1984).
Nutrition And Energetics
Metabolism And Temperature Regulation
No information, except incubating bird gular-flaps at ambient temperatures of 38–49°C (Allen 1942).
Drinking, Pellet-Casting, And Defecation
No information. Nestlings do not automatically regurgitate food when disturbed (Powell and Bjork 1990).