[17] Despite the similarities in most forms of the red-winged blackbird, in the subspecies of Mexican Plateau, A. p. gubernator, the female's veining is greatly reduced and restricted to the throat; the rest of the plumage is very dark brown,[18][self-published source?

[20] In the California subspecies, A. p. californicus and A. p. mailliardorum, the veining of the female specimens also covers a smaller surface and the plumage is dark brown, although not in the gubernator grade;[19] and also its superciliary list is absent or poorly developed.

[27] Unlike most North American passerines which develop their adult plumage in their first year of life so that the one-year-old and the oldest individual are indistinguishable in the breeding season, the red-winged blackbird does not.

[18] Both the peak male and the legs, the claws and the eyes are black;[34][28][35] in the female beak is dark brown and clear in the upper half at the bottom,[28] and the tail is medium in length and rounded.

On the other hand, the feathers of the yellow stripes of the males are devoid of carotenoids —except occasionally when they appear tinged with a pink coloration derived from small amounts of said pigments— and present high concentrations of pheomelanin —82% of all melanins.

[32] The fact that female red-winged blackbirds do not appear to consistently use variability in the size and color of male wing spots when choosing a mate runs counter to the classic role of carotenoid pigmentation ornamental feathers, mostly used in the attraction of a couple.

The male's song, accompanied by a display of his red shoulder patches, is a scratchy oak-a-lee,[45] except that in many western birds, including bicolored blackbirds, it is ooPREEEEEom.

[28] In the winter of 1975–1976, near Milan in western Tennessee, red-winged blackbirds were observed resting in a mixed roost that came to house 11 million individuals in January and early February in a plantation of 4.5 hectares of yellow pine (Pinus taeda) with little undergrowth was seen in soybean fields during the day, being that these constituted only 21% of the habitat in the area and that the other bird species present in the roost were not commonly observed in these fields; they were also common in cornfields.

[55] In that same study, reproductive individuals in upland habitats demonstrated a slight preference for old and new grasses such as Phleum pratense, Dactylis glomerata, Poa spp., Festuca spp., and Bromus spp.

[57][59] One found that red-winged blackbirds avoided the marsh wren (Pantaneros chivirenes), a predator common in nests of this species, reproducing among more dispersed vegetation, which was more easily defended from the chivirines; conversely, the chivirines seemed to prefer the denser vegetation, where they were more likely to avoid the aggressiveness of the red-winged blackbird; These differences in habitat selection between one species and another resulted in spatial segregation of their breeding areas.

It feeds primarily on plant materials, including seeds from weeds and waste grain such as corn and rice, but about a quarter of its diet consists of insects and other small animals, and considerably more so during breeding season.

[62] It prefers insects, such as dragonflies, damselflies, butterflies, moths, and flies, but also consumes snails, frogs, eggs, carrion, worms, spiders and mollusks.

[53] Studies of the stomachs of individuals of both sexes reveal that males consume higher proportions of crop grains, while females ingest a relatively larger amount of herb seeds and animal matter.

[67] A study in eastern Ontario found that although red-winged blackbirds began nesting earlier in years with warm springs, associated with low winter values in the North Atlantic Oscillation Index, egg laying dates remained unchanged.

[72] The red-winged blackbird can accommodate ectoparasites such as various Phthiraptera, the Ischnocera Philopterus agelaii and Brueelia ornatissima,[84] and hematophagous mites, like Ornithonyssus sylviarum,[84] and endoparasites like Haemoproteus quiscalus, Leucocytozoon icteris, Plasmodium vaughani, nematodes,[84] flukes and tapeworms.

[2] According to the American ornithologist Arthur Cleveland Bent, in the northern regions of its range the eastern red-winged blackbird is almost completely beneficial from an economic perspective and there are comparatively few complaints of severe crop damage.

In the Midwest, where these birds are much more abundant and where cereals are grown more extensively than in the North, red-winged blackbirds and other ichterids, in late summer and fall, do great damage to grain fields, both while they are maturing as when they are harvested .

[72][90] They also eat on Anthonomus grandis and Hypera postica, two species of weevils affecting cotton and alfalfa respectively, as well as harmful caterpillars of the European gypsy moth (Lymantria dispar) and of the genus Malacosoma.

[48] In some areas of the southern United States, the seeds of the common plumber (Xanthium strumarium), a weed detrimental to soybeans and cotton, seems to be an important food source for the species.

[53][51] Beal (1900) stated: In summarizing the economic status of the red-winged blackbird, the main aspect to consider is the small percentage that grains represent in their annual diet, which apparently contradicts complaints about its destructive habits.

[53] However, Bendell et al. (1981) found that the economic benefit of pest control, such as larvae of that lepidopteran, by the red-winged blackbird only compensated for 20% of the damage to crops caused by this bird.

A crew approached a roost in silence, hidden in the darkness of the night, and simultaneously lit the reeds at various points, which were quickly enveloped by a single great flame.

[53] Crop predation has led to the use of traps, poison and surfactants by farmers in an attempt to control populations of red-winged blackbirds;[28] these last properties suppress waterproof feathers, making them extremely vulnerable to the cold,[72][103] but their effectiveness depends on certain atmospheric conditions, namely low temperatures and rainfall.

[53] The ingestion of one or more of these particles by a blackbird causes erratic flight, calls for suffering and finally death; that behavior often leads the remaining birds in the flock to leave the field.

[53] In Brown County (Northeast South Dakota), in 1965, hand-spread 4-aminopyridine baits at intervals of about one week reduced projected red-winged blackbird loss by maturing corn crops by 85%.

[105] In another experiment in the same county, the number of blackbirds making use of the treated area fell dramatically over a period of five days after treatment had begun and remained low for the remainder of the season of damage to cornfields.

[105] A variety of devices to repel them, including electronic noise-making systems, helium balloons tied in the fields, radio-controlled aircraft, and various types of scarecrows are occasionally used in cornfields.

As a general ecological principle, diversity in the types of habitats that can be maintained in regions of intense agricultural activity is related to a greater probability that the damages caused by pests are restricted to economically tolerable levels.

[53] An alternative way to reduce populations of red-winged blackbird, and therefore the damage they cause to crops, involves implementing a program that is intended to interfere with their ability to reproduce, for example, through the use of sterilizing chemicals.

[54] In addition in Ontario, a negative relationship was found between the North Atlantic Oscillation Index (NAO) in the six months prior to a certain reproductive season and the size of the harems.