Food Habits

Main Foods Taken

Crustaceans if available (Heard 1983, Meanley 1985). Highly opportunistic, eating small crabs, slugs, minnows, aquatic insects, grasshoppers, small vertebrates, seeds (Simmons 1914), amphipods (Test and Test 1942), other bird’s eggs (Segre et al. 1968), and occasionally immobilized small birds (Spendelow and Spendelow 1980, Jorgensen and Ferguson 1982). Freshwater populations on lower Colorado River eat mostly crayfish (Procambarus clarki and Orconectes sp.), clams (Corbicula sp.), isopods, water beetles (Hydro-philidae) and small fish; saltwater populations in mangroves on West Coast of Sonora and Nayarit, Mexico, eat crabs, marine snails, and insects (Ohmart and Tomlinson 1977). On East Coast of U.S. and in n. South America, mostly fiddler crabs (Uca or Sesarma spp.; Fig. 2; Heard 1983, Hilty and Brown 1986). Consumption of seeds and vegetation increases in winter (Martin et al. 1951).

Microhabitat For Foraging

Forages within emergent vegetation or mangroves, or along edges between marsh and mudflats (Clark and Lewis 1983, Meanley 1985, Zembal and Fancher 1988). Foraging habitat on East and Gulf Coasts determined mainly by abundance of emergent vegetation or mangroves, secondarily by presence of fiddler crabs (Clark and Lewis 1983). Regularly ventures onto mudflats and algal mats with gently sloping shorelines at low tide or after wind-driven low tides in the evening (Simmons 1914, Lewis and Garrison 1983, Zembal and Fancher 1988). Forages for crabs by searching along central drains of tidal creeks at low tide (Zembal and Fancher 1988). Feeds during high tides on prey on grass stalks (Meanley 1985). In Arizona, forages at sites with high mean coverage by water, low stem density relative to other sites in marsh, and moderate water depth (about 7.5 cm)—traits of newly formed marsh areas (Eddleman 1989, Conway et al. 1993).

Food Capture And Consumption

Sight feeder, moving erratically in response to cues; does not often probe deep in substrate (Simmons 1914, Williams 1929, Meanley 1985, Zembal and Fancher 1988). Rails have highly developed olfactory process with many mucous cells, and have large olfactory bulb in the brain, indicating that they may be able to use smell to assist in locating prey; deserves further study (Bang and Wenzel 1985).

Surface-gleaning and shallow probing account for 90% of time spent foraging in s. California (Zembal and Fancher 1988). Searching for crabs (“crabbing”), foraging on mudflats, fishing, and scavenging account for the remaining 10% of time. Often average 675 gleans/h; sometimes up to 2,000 gleans and probes/h (Zembal and Fancher 1988). Obtains prey after 18.2–52.9% of attempts. Success rate lowest for crabbing or casual foraging, and highest at prey concentrations. Average 250 morsels of tiny prey/h during foraging bouts (Zembal and Fancher 1988). Moves 0.2–10 m between foraging bouts; travels the most during crabbing. Crabbing bouts last 1–3.5 h (Zembal and Fancher 1988). At high tide in Virginia, may probe into fiddler crab (Uca spp.) burrows and moves rapidly from burrow to burrow; forages slowly and deliberately at low tide (Meanley 1985).

Swallows smaller crabs and other crustaceans whole; dismembers medium-sized crabs by shaking them, then swallows the parts whole; dismembers larger crabs and swallows parts whole, and breaks open body and consumes only flesh (Bent 1926, Meanley 1985, Zembal and Fancher 1988, WRE). Sometimes rinses clams in water to remove mud, then swallows them whole or breaks them and eats the contents (Williams 1929). Remains of prey items often found on constructed platforms in marsh or on muskrat (Ondatra zibethicus) houses throughout range, suggesting that some prey may be trans-ported and eaten at central location (Meanley 1985, WRE).

Major foods in Arizona peak in abundance during time of hatching and brood-rearing (Conway 1990). Lowest food abundance in winter, and increased movements by rails at that time of year may be a response to this decline.

Major Foods Items

Birds from e. U.S. eat mainly fiddler crabs and other small crabs; shrimp (especially Orchestia grillus), amphipods, insects, snails, clams, polychaete worms (Nereis succinea), fish; and cordgrass, bulrush (Scirpus spp.), sedges, smartweed (Polygonum spp.), oak (Quercus spp.), and soybean (Glycene max) seeds (Martin et al. 1951, Heard 1983). Principal prey of West Coast subspecies includes crabs (Pachygrapsus crassipes and Hemigrapsus oregonensis), ribbed horse mussels (Modiolus demissus), spiders (Lycosidae), little macoma clams (Macoma balthica), California horn snails (Certhidea californica), salt marsh snails (Melampus olivaceus), crayfish (Procambarus sp.), beetles, other insects, isopods, pickleweed and Pacific cordgrass vegetation, seeds, and small fish (Moffitt 1941, Zembal and Fancher 1988). Diet of 278 Clapper Rails collected year-round on East Coast consisted of 96% animal prey and 4% plant items (Martin et al. 1951). Plant material is not part of summer diet, and makes up 3% of fall diet, 11% of winter diet, and 1% of spring diet (Martin et al. 1951).

Quantitative Analysis

Food of 124 Clapper Rails collected in summer from range of all 5 eastern subspecies was mainly fiddler crabs (Uca pugnax found in 29.8% of the birds; U. largisignalis, 16.9%; U. pugilator, 4.8%; U. rapax, 7.2%; U. panacea, 8.1%; U. speciosa, 1.6%; Sesarma reticulatum, 17.7%; S. cinereum, 3.2%); species eaten depends on location of collection and geographic range of crab (Heard 1983). Other crabs eaten were Aratus pisonii (3.2% occurrence), Eurytium limosum (4.8%), Panopeus herbstii (0.7%), and Rhithropanopeus harrisii (0.7%). Remainder of diet included shrimp (Palaemonetes pugio, 0.7%); amphipods (Orchestia grillus, 9.7%); insects (Orchelimum fidicinum, 5.6%); ants (Formicidae, 0.6%; and unidentified, 5.6%); Gulf periwinkle (Littorina irrorata, 10.5%); southern periwinkle (L. angulifera, 0.6%); salt-marsh snails (Melampus bidentatus, 6.5%); coffee bean snail (M. coffeus, 3.2%); ribbed mussel (Geukensia demissa, 0.7%); and stout tagelus (Tagelus plebeius, 0.7%); clam worms (Nereis succinea, 7.3%); pinfish (Lagodon rhomboides, 0.7%); and acorns (0.7%). In Louisiana, 15 nesting birds ate fiddler crabs (Uca spp.; 100% occurrence, 95% volume), salt marsh snails (30%, 4%), fish (12%, <1%), and insects (6%, <1%; Roth 1972).

In S. Carolina, 284 birds collected in autumn ate fiddler crabs (Sesarma cinereum, 58% occurrence, 33% volume; S. reticulatum, 37%, 15%; Sesarma sp., 17%, 6%; Uca spp.; 45%, 14%); other crabs (18, 6); periwinkle snails (37%, 14%); moth larvae (Noctuidae; 12%, 6%); and other insects (3% volume; Oney 1951). Other small invertebrates, killifish (Fundulus sp.), and cordgrass made up trace of diet. Clapper Rails collected in fall in Louisiana had similar diet dominated by crabs, snails, and plant debris (Bateman 1965). One hundred birds collected at Wallops I., VA, in autumn ate crabs (50% of volume); grasshoppers and allies (Orthoptera; 35%); spiders (5%); and miscellaneous insects, periwinkle snails, and plant material; while 80 birds collected at Gargathy Bay, VA, ate grasshoppers (60% of volume), fiddler crabs (20%), snails (10%), and other insects (10%; Meanley 1985).

In Louisiana, winter diet is more varied than summer and fall diet; 103 birds ate crayfish (Procambarus sp., 20% volume), fiddler crabs (Uca spp., 5%; Sesarma spp., 2%), insects 29%), snails (Polygyra sp., 6%; others, 3%), clams (Ragina sp., 4%), rodents (3%), skink (Eumeces sp., 2%), frogs (Pseudacris sp., 1%; others, 2%), and plant material (cowpea [Vigna repens], 9%; other, 2%; Roth 1972).

In San Francisco Bay, CA, Clapper Rails collected in Feb ate ribbed horse mussels (56.5% of volume); spiders (Lycosidae, 15.0%); seeds and hulls of cordgrass (14.6%); little macoma clam (7.6%); mud crabs (3.2%); worn-out nassa (Ilyanassa obsoletus; 2.0%); and insects, clam worms (Nereis spp.), and carrion (total 1.1%; Moffitt 1941).

Considerable variation in diet of Yuma Clapper Rail during breeding season, depending on location (Ohmart and Tomlinson 1977). Above Imperial Dam on Colorado River in sw. Arizona and se. California, diet of 9 birds was crayfish (94.7% volume), weevils (Curculionidae, 2.8%), ground beetles (Carabidae, 0.1%), other beetles (0.6%), damselfly nymphs (Odonata, 0.1%), grasshoppers (0.1%), other insects (0.8%), insect eggs (0.1%), spiders (0.6%), clams (Corbicula sp., 0.1%), mammal bones (0.1%), and seeds (0.1%). At mouth of Gila River in Arizona, 2 birds ate isopods (48.5% volume), clams (50.0%), and insects (1.5%). In Colorado River delta of nw. Sonora, Mexico, 4 birds ate water beetles (56.6% volume), fish (31.8%), leeches (Hirudinea, 3.8%), seeds (2.8%), twigs (2.5%), damselfly nymphs (2.0%), dragonfly nymphs (0.5%), and shrimp (Palaemonidae, 0.2%). Diet of 16 birds collected in coastal Sonora and area of San Blas, Nayarit, Mexico, was similar to that of other subspecies in mangrove wetlands (Ohmart and Tomlinson 1977).

Opportunistic and omnivorous; food selection reflects mainly salinity of marsh type and geographic location (Heard 1983).

No information.

No information.

Owing to its salt glands, capable of drinking either fresh water or seawater (Conway et al. 1988, Hammons et al. 1988). Total body water (mean 68.3% ± 2.8 SD, n = 16) and total body mass not affected by acclimation to seawater (Hammons et al. 1988). Mean daily water flux of freshwater-adapted birds (290 ml/kg ± 70 SD, n = 16) reduced after acclimation to salt water (255 ml/kg ± 20 SD, n = 12). Average daily water flux 71 ml/d for a 280-g individual (n = 8; Hammons et al. 1988). Solute concentration of salt gland secretion of birds acclimated to salt water was similar, but flow rate of secretions was only 10% that of marine gulls (Conway et al. 1988). May ingest ice during prolonged cold weather (Meanley 1969).

Regurgitates pellets consisting of fragments of crustacean exoskeletons, mollusk shells, insect exoskeletons, and seeds (Meanley 1962, Zembal and Fancher 1988). Pellets usually cast in con-cealed locations where birds hide and consume prey (e.g., grassy runways, bushes, clumps of grass), or at high spots such as muskrat houses (Meanley 1962).