About Porzana carolina (Linnaeus, 1758)
Scientific name: Porzana carolina (Linnaeus, 1758). Description. Adult soras measure 19–30 cm (7.5–11.8 in) in length, and weigh 49–112 g (1.7–4.0 oz), with a wingspan of 35–40 cm. They have dark-marked brown upperparts, a blue-grey face and underparts, and black-and-white barring on the flanks. They have a short, thick yellow bill, with black markings on the face at the bill's base and on the throat. The sexes are similar in appearance. Young soras lack the black facial markings, and instead have a whitish face and buff breast. Soras produce two common calls: a loud, squeaking decelerating "whinny" that drops in pitch, which they often use to advertise territories; and a softer, ascending "ker-wee" or "sor-ah". The latter call is sometimes suggested as a possible origin for the species' common name. Distribution and habitat. The sora is common across most of North America: it occurs naturally in 49 US states (Hawaii is the only exception), all 10 Canadian provinces, and two Canadian territories. Outside the US and Canada, the species is found throughout Central America, the Caribbean, and northern South America. It has also been recorded as a vagrant in Iceland, Great Britain, Portugal, and at Lake Titicaca. Soras breed in a range extending from Nova Scotia northwest to southern Yukon and the Northwest Territories, south to California, Arizona, and New Mexico, and northeast to Pennsylvania and New England. Sora wintering grounds span the Caribbean, northern parts of South America (including Ecuador, Colombia, and Venezuela), north through Central America and Mexico to southern California in the West and coastal regions of the Southeast. From southern Kansas south to northern and eastern Texas, and east through the inland areas of the southeastern United States, soras are typically only observed during spring and fall migration. In a few areas of the western United States, including central California and parts of Arizona and New Mexico, soras may occur year-round. Individual sora home range size varies. In northwestern Iowa, brood-rearing home ranges averaged 0.5 acres (0.20 ha). In Arizona, home range size ranged from 1.5 acres (0.61 ha) in the early breeding season to over 2 acres (0.81 ha) in the postbreeding season; these seasonal differences in home range size were not statistically significant (p>0.05). Reported densities vary from 12 soras per acre in Colorado to 0.47 pairs per ha in Indiana. An average of 1.3 soras per ha responded to call surveys across sites in Colorado, and a similar density was found in southeastern Wisconsin. In Iowa, the average density across two years and multiple marsh habitats was 1.3 pairs per ha. Landscape factors including marsh area, habitat edges within marshes, and the number of marshes in a region may influence soras. While soras occur in marshes of all sizes, they may reach higher densities in intermediate-sized marshes. In east and central Maine, soras presence was significantly (p≤0.01) positively correlated with total wetland area and perimeter area of surface water, and in Saskatchewan they were significantly (p<0.05) positively correlated with wetland area. In Maine, soras used 10% of 2.5-acre (1.0 ha) wetlands, 40% to 50% of wetlands 2.5–5 acres (1.0–2.0 ha) in size, and 20% of wetlands larger than 50 acres (20 ha). In western New York, soras were significantly (p=0.007) more abundant in marshes 100 to 250 acres (40 to 101 ha) in size than in smaller (< 100 acres (40 ha)) or larger (250–380 acres (100–150 ha)) marshes; additionally, sora nests were detected more often in 100–200 acres (40–81 ha) marshes. Soras are commonly found in plant communities dominated by cattails (Typha spp.), sedges (Carex spp.), bulrushes (Scirpus spp.), smartweeds (Polygonum spp.), rushes (Juncus spp.), rice cutgrass (Leersia oryzoides), and barnyard grasses (Echinochloa spp.). Soras also appear to prefer edge habitats. Breeding sora density was significantly (p<0.001) correlated (r=0.62) with the perimeter-to-area ratio of northwestern Iowa marshes. The distance from the center of sora territories to a habitat edge was also significantly (p<0.005) smaller than the distance from the center of Virginia rail territories to a habitat edge. In Arizona, habitat edges were closer to areas heavily used by soras than to randomly selected sites. Large-scale wetland dynamics can affect soras: in the prairie pothole region of North Dakota, sora population indices at three "levels of response" were significantly (p<0.01) correlated (r≥0.70) with the number of ponds present in May. Outside of wetlands, soras are most often reported in cultivated areas during migration or the postbreeding period. For example, a sora was observed 3 mi (4.8 km) from marshland in a cultivated Iowa field in mid-August. A male sora was observed less than 1,000 ft (300 m) from a large wetland in a soybean (Glycine max) field in northwestern Iowa during the postbreeding period. From early June to mid-July, soras were observed on Saskatchewan farms sown mainly with wheat (Triticum aestivum). Soras have also been reported in flooded wooded areas. In western New York, soras occurred during the breeding season on a study site where 26% of the area was categorized as "flooded timber," and 5% was classed as "scrub/shrub marsh". In eastern and central Maine, an average of 2.1 soras was observed in wooded swamps per 100 hours of observation during the breeding season. On a nonbreeding (August–April) site in southwestern Arizona, soras used a "mixed shrub community" more often than expected based on its availability. Soras were observed at low abundances on a site with Douglas-fir (Pseudotsuga menziesii), ponderosa pine (Pinus ponderosa), and trembling aspen (Populus tremuloides) in British Columbia. Soras use areas with a wide range of water depths. They are often observed in water less than 1 ft (30 cm) deep, although the average water depth of heavily used sora areas in Arizona was 20 in (51 cm). In northwestern Iowa, the average water depth in sora territories was 15 in (38 cm), which was significantly (p<0.025) shallower than water depths at random marsh locations. Sora nesting sites occur in shallower water than random sites in western New York. Average reported water depths at nest sites range from 4 in (10 cm) for 4 sora nests in Colorado to nearly 10 in (25 cm) for sora nests in western New York. In deep water areas, soras typically wade on mats of floating vegetation. Water level fluctuations may result in nest abandonment: for example, at a Colorado site where water levels rose more than 8 in (20 cm), a sora nest holding 7 eggs was abandoned. In Alberta, soras nested in more vegetation types during a drought year, most likely due to substantially reduced water levels in the vegetation they used the previous year. Soras use shallower water in fall than in spring, and typically avoid open water. There is a significant (p≤0.05) negative relationship between open water area and sora wetland use in Maine, and between sora relative abundance and open water area in Saskatchewan. In western New York, sora nesting sites had a lower percentage of open water than random sites, and in Arizona soras used open water areas less often than their availability would suggest. Sora nesting sites had a larger percentage of emergent vegetation than random sites in western New York marshes. In northeastern North Dakota wetlands, sora numbers were significantly (p<0.05) positively correlated (r=0.45) with hectares of live emergent vegetation. In east and central Maine, wetlands used by soras had significantly (p=0.01) greater emergent vegetation area than unused wetlands. The density of emergent vegetation in sora habitat varies: reported average density ranges from 121.9 stems per m2 in northwestern Iowa sora territories to 333 stems per m2 on northeastern Missouri sites used during fall migration. In western New York, 95% of sora nests had vegetation cover greater than 70%. In addition, nesting sites had more horizontal cover 20 inches (0.5 m) above water level than random sites. However, average stem density on sora territories was not significantly (p>0.05) different from stem density at random sites in northwestern Iowa. The height of emergent vegetation in sora habitat also varies, ranging from 8 to 11 in (20 to 28 cm) in the spring after winter disturbance in northwestern Iowa to 84 in (210 cm) in heavily used sora areas in Arizona. In western New York marshes, the average vegetation height at sora nesting sites was shorter than at random locations. However, the average height of emergent vegetation in northeastern Iowa sora territories was not significantly (p>0.05) different from vegetation height in random plots. In Arizona, both vegetation cover and height used by soras varied with seasons; Conway suggested these differences likely reflect the sora's varied diet, while seasonal differences in habitat availability are another possible explanation for seasonal differences in sora habitat. The extent of woody vegetation surrounding South Dakota wetlands was not significantly (p=0.6) associated with sora occurrence. However, in western New York marshes, there was a significant (p=0.041) negative relationship between the percentage of flooded timber on a site and sora relative abundance. Soras may prefer certain cover types. In Arizona, 65.3% of sora use was in southern cattail (Typha domingensis), although this species made up only 16.5% of the vegetation present. Bulrushes and a mixed-shrub community were also used more often than their availability, while saltcedar (Tamarix chinensis) and arrowweed (Pluchea sericea) were avoided. A literature review notes that soras avoid sites dominated by purple loosestrife (Lythrum salicaria). In east and central Maine, wetlands used by soras had significantly (p<0.05) more ericaceous vegetation, such as leatherleaves (Chamaedaphne spp.), sweetgales (Myrica spp.), and laurels (Kalmia spp.). In northwestern Iowa marshes, broadleaf arrowhead (Sagittaria latifolia) occurred in sora territories significantly (p<0.01) more often than at random sites; Johnson and Dinsmore imply this likely results from both species preferring similar site conditions. In May and June in Wisconsin, soras were detected significantly (p<0.025) more often in cattail (Typha spp.) survey areas than in sedge areas. However, in southeastern Wisconsin during the breeding season, there was no significant (p=0.943) difference in sora densities between habitats composed predominantly of cattail, sedge, or bulrush. Additionally, soras' use of glaucous cattail (Typha × glauca), broadfruit bur-reed (Sparganium eurycarpum), sedge, river bulrush (Schoenoplectus fluviatilis), and hardstem bulrush (S. acutus var. acutus) habitats in northwestern Iowa marshes generally matched the availability of these habitats. Seasonal differences in sora habitat use have been reported. In northeastern Missouri in spring, the likelihood of detecting soras in robust emergents such as cattails (Typha spp.) and longroot smartweed (Polygonum amphibium var. emersum) was over 6 times higher than it was in fall. However, the study did not address habitat availability at different times of the year. In a study conducted in southeastern Missouri, plant species used by soras during spring and fall migration differed significantly (p=0.005), but the author qualifies this finding by noting major seasonal differences in vegetation availability. Temperature may also influence sora abundance. In Colorado, average April temperature was significantly (p<0.01) negatively correlated (r= -0.94) with sora abundance. On sites with average April temperatures ≤ 42 °F (6 °C), soras were more abundant than the closely related Virginia rail (Rallus limicola), while on warmer sites the ratio of soras to Virginia rails declined. Food and feeding. Soras eat a wide range of foods. Common animal prey items include snails (Gastropoda), crustaceans (Crustacea), spiders (Araneae), and insects (Insecta), mainly beetles (Coleoptera), grasshoppers (Orthoptera), flies (Diptera), and dragonflies (Odonata). Soras often eat the seeds of plants including smartweeds, bulrushes, sedges, and barnyard grasses. In the eastern United States, soras eat seeds of annual wildrice (Zizania aquatica) and rice cutgrass. A literature review lists crowngrass (Paspalum spp.) and rice (Oryza sativa) as relatively important food sources for soras in the Southeast. Plants making up less than 5% of the sora's diet are also recorded, and include spikerushes (Eleocharis spp.), duckweeds (Lemnaceae), pondweeds (Potamogeton spp.), panicgrasses (Panicum spp.), cordgrasses (Spartina spp.), and saltgrass (Distichlis spicata). Soras eat more plant food in fall and winter (68%–69%) than in spring and summer (40%). Plant material such as hairy crabgrass (Digitaria sanguinalis), fall panicgrass (Panicum dichotomiflorum), and bristlegrass (Setaria spp.) occurred at substantially higher frequencies and in much larger volumes in sora esophagi collected in southeastern Missouri during fall migration than in those collected in spring. Additionally, animals made up a larger volume of the spring diet than the fall diet. The volume of animal material in spring-collected esophagi was predominantly composed of adult beetles and snails from the Physidae family.
