Rallus aquaticus

Rallus aquaticus

The water rail (Rallus aquaticus Linnaeus, 1758) is a bird belonging to the Rallidae family.

Systematic –
From a systematic point of view it belongs to:
Eukaryota domain,
Kingdom Animalia,
Phylum Chordata,
Aves class,
Order Gruiformes,
Rallidae family,
Rallus genus,
Species R. aquaticus.
The following subspecies are recognized within this species:
– Rallus aquaticus subsp. aquaticus;
– Rallus aquaticus subsp. hibernans Salomonsen, 1931;
– Rallus aquaticus subsp. korejewi Zarudny, 1905.
The Rallus. a. aquaticus Linnaeus, 1758, the nominal subspecies; it is present in Europe, North Africa, Turkey and western Asia, up to the Caspian Sea and western Kazakhstan, as well as, further east, in a strip of land that reaches up to central Siberia.
The Rallus. a. hibernans † Salomonsen, 1931, endemic to Iceland is an extinct subspecies; it presented the upper regions of a somewhat lighter brown than the nominal form. The flank stripes were dark brown, not black, and the beak was shorter; the gray of the nether regions could take on a brown hue. This subspecies disappeared around 1965, due to habitat destruction caused by the draining of wetlands and predation by the American mink, introduced by man.
The Rallus. a. korejewi Zarudny, 1905. It is present in central-southern Asia, from the southern and eastern regions of Iran to western China, as well as in Kashmir and Ladakh (Indian subcontinent). It is slightly larger than the nominate subspecies, and has a lighter brown upperpart and a lighter slate-blue underpart. It has a faint brown streak across the eye.

Geographic Distribution and Habitat –
The Rallus aquaticus is a bird native to the regions between Western Europe and Central Asia. Nordic populations migrate to wintering areas in the Mediterranean region and southwestern Asia.
Its range is, however, discontinuous, stretching from Iceland and the British Isles to Siberia and China; where there are habitats favorable to it; it is also present in North Africa, Saudi Arabia and Türkiye. In Asia it has not yet been carefully studied, so it could occupy a wider range than previously known.
This bird is occasionally present even in locations considered inappropriate.
The nesting habitat of this species is that of permanent wetlands with stagnant or slow-flowing waters, both fresh and brackish, and dense vegetation, made up of plants such as marsh reeds, cattails, irises, cutlasses or sedges.
In nesting sites located in coastal marshes, the habitat is dominated by sea rush, or by sedges and cutlass where the soil is less saline. A study in the Netherlands and Spain showed that rushes provide better hiding places than other maritime plants. In other places, nests are built from the nearest available plant materials. Where they are present, sedge patches, a plant up to 1.5 m tall, guarantee an excellent site for nesting. However, its preferred habitat is the Phragmites reed beds which develop in waters 5–30 cm deep, with muddy soil in which to search for food and a rich variety of invertebrate species. Over large areas with a uniform habitat, areas close to willows or shrubs are preferred. In addition to natural freshwater or saltwater marshes, this bird can also settle in gravel, clay and peat pits, provided they offer sufficient shelter. It can be found in rice fields or on floating islands of vegetation, and in Kashmir it is present in flooded sugar cane fields.
The northern limit of the breeding range appears to be determined by the transition between nutrient-rich wetlands and less productive, more acidic waters. This leads to the replacement of reed beds with more open vegetation, dominated by marsh cinquefoil (Comarum palustre), inadequate for the survival of Rallus aquaticus.
During the migration period and in winter, this species moves into various types of wetlands, including flooded thickets or expanses of ferns. Intense cold can push the bird into more open locations, such as canals, landfills and gardens, or even onto snowy expanses. In Wales, researchers have found that the winter ranges of this species overlap, with each individual using a significant portion of reeds. After abandoning their summer sites in the cold months, the birds return to their usual range. Densities of 14 specimens per hectare have been recorded. Birds that wintered in Iceland relied on hot geothermal springs, which they reached through tunnels dug under the snow. When they weren’t foraging for food, they hid in the hollows and crevasses of solidified lava. Sometimes, R. aquaticus goes well beyond the boundaries of its range and erratic specimens have been found in the Azores, Madeira, Mauritania, the Arctic, Greenland, Malaysia and Vietnam. In Italy the population is constant and exclusively migratory, often migratory individuals passing through the peninsula pass by resting in humid territories.
Although it is predominantly a lowland species, it nests up to 1240 m in the Alps and at 2000 m in Armenia. In Italy, a study has shown that birds present in reed beds require wetlands of a certain size, which is approximately one hectare, although the highest densities are found in marshes of 10 hectares or more.

Description –
The Rallus aquaticus is a bird with dimensions around 26-29 cm in length, weighing 90-120 grams and a wingspan of 38-45 cm. There is slight sexual dimorphism with females being a little smaller than males, with a thinner bill; however, it is not sufficient to determine the sex of a specimen based on measurement alone.
The color of the plumage of the upper regions, from head to tail, is olive-brown with black streaks, especially on the shoulders. The sides of the head and the lower regions, up to the lower part of the abdomen, are instead of a dark slate-blue colour, with the exception of a blackish area between the beak and the eye and a brownish area on the sides, at the height of the upper chest. The flanks are striped with black and white, and the undertail is white with some darker stripes.
The long beak and iris are red and the legs are flesh-brown.
Young specimens have a blackish top of the head and a white chin and throat. In them the underparts are buff or white with darker stripes, and the patterns on the flanks are brown and buff, rather than black and white. The undertail is buff-colored, and the eye, beak and legs have a less vivid color than that of adults.
The chicks are covered in black down and have white beaks.
After the nesting period, the bird molts and cannot fly for about three weeks.
Adult specimens can be recognized by the undertail designs, which differ from one specimen to another.
Adult males have the undertail thickly covered with black stripes. It has been hypothesized that the dark stripes of the undertail of this species constitute a sort of compromise between the signaling function of a completely white undertail, as in the case of species that venture into open waters or with gregarious habits such as the moorhen, and the need not to make oneself too obvious.
The eggs are blunt and ovoid, smooth and slightly shiny; the color varies from dirty white to buff-pink, with some reddish-brown patches around the greater pole, which can sometimes come together in a single patch. The differences in the size of the eggs of the three subspecies are smaller than those found between individual eggs; the size of the eggs of the nominal subspecies is 36×26 mm and is also valid for those of the other subspecies. Each egg weighs approximately 13 g, of which 7% is made up of the shell.
As regards the call, this bird is quite noisy; in fact it makes its main call heard throughout the year.
The song consists of a series of grunts followed by a squeal similar to that emitted by a piglet, followed by more grunts. It is used as a territorial, alarm and announcement call. Members of the same pair can issue this call alternately; in this case, the male emits lower and slower notes than his partner. The courtship song, emitted by both sexes, consists of a tyick-tyick-tyick which often ends with a trill emitted by the female; the male is capable of singing for hours. Among the other sounds produced we remember the flight call, consisting of a high-pitched whistle, a strong repeated squeak emitted by the male when he shows the site where to build the nest to the female, and a sort of buzz emitted by both parents when they are in the nest with the chicks. Water rails are noisier when they settle into an area and at the beginning of the nesting season, when the calls can last until late at night. The chicks barely peep at first, but soon they begin to make a call for food that sounds like a tyk-tyk-trik.

Biology –
The Rallus aquaticus is a monogamous species, extremely territorial during nesting.
Pairs reunite after arriving on the breeding grounds, or perhaps even before spring migration.
In larger marshes, which offer more favorable conditions, pairs can nest 20–50 m apart.
The nesting territory varies in size, but generally extends for 300 m². Members of a pair court each other and make contact calls throughout the mating season.
The male chooses the site where to build the nest, indicating it to the female while she poses by raising the feathers on her back, arching her wings over her back, widening her tail and pointing her beak vertically downwards. This posture is accompanied by a strong call. Before mating, the male raises his wings and tail, and lowers his beak until it touches his chest.
During the courtship phase the male brings food to his partner, and, during incubation, the female can momentarily abandon the nest to perform in front of the male, walking around him, emitting soft calls, rubbing her beak against his and performing short runs back and forth.
The nest is built with any type of vegetation available and is created mostly by the male, generally in the course of a single day.
The nest measures 13–16 cm wide and about 7 cm high, with a total weight of around 95 g; this rises 15cm or more above bog level and is sometimes built on root blocks, tree stumps or similar supports. If the water level of the swamp begins to rise, it can be built on a higher point. It is well hidden and is connected to the surrounding terrain by a series of narrow paths.
The female lays an average of 6-11 eggs, with fluctuations linked to the range.
The date of deposition also varies from place to place, ranging from the end of March in Western Europe and North Africa, to the end of May in Kashmir, and to June in Iceland.
Typically, broods laid at the beginning or end of the breeding season may be smaller, and the nesting season may also be prolonged if the brood is lost and needs to be replaced or if a further brood is laid.
The brood is cared for by both parents, although most of the work is done by the female.
The incubation period is 19-22 days, with a reproductive success of around 87%; the chicks, precocious and covered in down, fly away 20-30 days after birth.
The food is provided by both parents and, precisely, by the parent who does not take care of the brooding; it is passed to the partner sitting on the nest before the latter delivers it to the young, although they are able to feed themselves already from the fifth day of life.
After fledging, the young rely solely on their own resources.
Fledging occurs around the age of 7-9 weeks.
In case of danger due to the presence of predators, the female can transport the chicks or eggs one at a time to another place; the eggs are carried in the beak, but smaller chicks may be carried under the wing. When an intruder arrives, the hatching bird may remain motionless on its eggs, attack the invader, or feign injury to create a sort of diversion.
The sexual maturity of this species is after one year of age, and the litters raised are generally two per year.
As for the average survival after fledging, it is around 17-20 months, with an annual survival rate of just under 50% per year for the first three years, and a little more thereafter.
The maximum age recorded for this species is 8 years and 10 months.

Ecological Role –
The oldest known fossils of ancestral Rallus aquaticus are represented by Carpathian bones dated to the Pliocene (1.8-5.3 million years ago). In the late Pleistocene, two million years ago, fossil evidence suggests that this species was present throughout much of its current range. This species is well documented, with over 30 reports from Bulgaria alone and many more from across southern Europe and China.
In Italy this bird is sedentary and nests in almost all regions, with greater diffusion in the Po Valley and in the medium-upper Tyrrhenian side. Large areas of non-presence are observed in the Alps, the Apennines and in some central-southern regions. The estimate of the breeding population is represented by 3,000-6,000 pairs, with a globally stable trend but characterized by local fluctuations.
In general it is an elusive species and its striped plumage makes it difficult to spot in the wetlands where it lives. The laterally flattened body allows it to glide through the thickest vegetation; if caught outdoors, it remains motionless. Moves with long strides, although cowers when running for cover. It is able to swim, if necessary, with the spasmodic style typical of rails, as well as flying short distances with its long legs dangling.
Although its flight is rather weak, it is capable of moving long distances, flying at night, and sometimes some specimens have died following collisions with headlights or electrical cables. Individuals ringed in Great Britain have been recovered in Poland, ex-Czechoslovakia and Sweden.
As far as food is concerned, this species is omnivorous, but it mainly feeds on animals. Among these we remember leeches, worms, gastropods, small crustaceans, spiders, and a wide range of insects, both terrestrial and aquatic, and their larvae. It also eats small vertebrates, such as amphibians, fish, birds and mammals, as well as carrion. Vertebrates are struck with a jab of the beak which fractures their spine.
Among the plant substances, consumed mainly in autumn and winter, it eats buds, seeds, flowers, roots and seeds of aquatic plants, berries and fruit.
In South Asia, it also sometimes eats harvested rice seeds. The young specimens feed mainly on insects and spiders. Food collected on earth or in mud is usually rinsed in water before being ingested. After the rain this bird usually patrols areas of soft ground in search of earthworms. Only rarely does it go looking for food in open areas, even when it is forced to do so in harsh climates.
To look for food, the Rallus aquaticus follows well-defined paths, frequently returning to the areas where the preys are more numerous.
From a food point of view they are versatile and opportunistic birds. They jump to catch insects sitting on plants, climb to pick berries, or pick apples from trees so they can eat them more peacefully on the ground. They kill other birds by impaling them on their beaks or drowning them, especially if the prey’s escape capabilities are restricted.
They are also raiders of nests, in particular those of the small birds that nest in the reeds such as the reed warbler.
R. aquaticus can defend their own winter foraging territory, smaller in size than the one used during the nesting season: in it the various specimens keep about 10 m away from each other; favorite sites can house hundreds of these birds. Outside the breeding season, aggressive attitudes can also be directed towards other Marsh Rails.
R. aquaticus defends its nesting and wintering area. It charges with its neck outstretched, and sometimes both members of a pair attack together. Clashes between males are more frequent in winter, when direct aggression is replaced by particular threatening postures, which consist of standing erect on the tips of the fingers, shaking the head and pushing the beak forward.
Among the predators and parasites it should be remembered that this bird can have a large number of mammals and large birds. As mentioned, the American mink was responsible for the disappearance of the Icelandic subspecies, and sometimes even cats and dogs kill specimens. At least in certain locations, otters capture these birds which also fall victim to the Eurasian bittern, another bird native to reed beds, as well as gray herons.
This bird is particularly vulnerable to attacks by herons when they are forced to abandon the safety of the reeds due to particularly high tides. However, their main predators are harriers, which usually hunt in wetlands; more rarely, R. aquaticus have also been seen captured by more unusual predators, such as tawny owls, short-eared owls, eagle owls and other species.
As for its parasites, the main ones include the bloodsucking lice Nirmus cuspidiculus and Pediculus ralli, the tick Ixodes frontalis and the horse fly Ornithomyia avicularia.
Furthermore, this bird can be infected by the avian influenza virus and by the bacterium Borrelia burgdorferi, transmitted by ticks of the genus Ixodes, a pathogenic agent which causes Lyme disease in humans. However, other parasites have been found at other sites in various parts of the world.
As regards its ecological status, the Rallus aquaticus is a decreasing species, but its total population still has a number of adults equal to 100,000-1,000,000 units and extends over an area of 15,600,000 km²; for this reason the species is classified among those of “least concern” on the IUCN Red List.
In most European countries the population is still stable or slightly decreasing due to habitat loss. In Morocco, however, both the range and the population are growing, and the species has spread as far south as the Souss-Massa National Park. Regarding the situation of Asian populations, there is little information, but we know that the subspecies R. a. korejewi is still very common in Pakistan and Kashmir.
Among the factors of greatest risk for the consistency of the populations of R. aquaticus there are obviously the predators mentioned but also the regression of the habitats, the reclamations carried out in certain habitats, the canalization of water courses, the advance of human settlements and from pollution.
Furthermore, this bird has been hunted for food for thousands of years; the Romans greatly appreciated its meat and depicted it on the wall paintings of Pompeii; the consumption of its meat continued throughout the Middle Ages up to the present day. However, due to its inaccessible environment and elusive nature, hunting does not appear to pose a serious threat to its survival.

Guido Bissanti

Sources
– Wikipedia, the free encyclopedia.
– GBIF, the Global Biodiversity Information Facility.
– C.Battisti, D. Taffon, F. Giucca, 2008. Atlas of nesting birds, Gangemi Editore, Rome.
– L. Svensson, K.Mullarney, D. Zetterstrom, 1999. Guide to the Birds of Europe, North Africa and the Near East, Harper Collins Publisher, United Kingdom.

Photo source:
– https://inaturalist-open-data.s3.amazonaws.com/photos/260674224/original.jpeg