Ardea purpurea

Geographic Range

Purple herons Ardea purpurea are a wide ranging bird species. They are year-round residents in southern Africa excluding Nambia. They also reside year-round in India, Myanmar, Bangkok, Singapore, Hong Kong, and the Jakarta and Indonesian islands. Subspecies of the purple heron include: Ardea purpurea madagascariensis residing in Madagascar, Ardea purpurea manilensis in Asian countries, and Ardea purpurea bournei only found in Cape Verde.

Purple herons have a vast breeding range scattered throughout the Palearctic Region that includes Eurasia. The patchy distribution includes as far north as Amsterdam, Spain, Greece, eastward to Kazakhstan. They have scattered populations in Saudi Arabia, Iraq, and Iran.They also have non-breeding populations in eastern China, North Korea, and the southeastern portion of Russia.

• Biogeographic Regions
• palearctic palearctic
• oriental oriental
  • native native
• ethiopian ethiopian
  • native native

Habitat

Purple herons live at elevations from sea level and 1800 meters. They spend their winters and breeding seasons living in shallow freshwater wetlands, as well as some river edges, ponds, and swamps. All habitats have considerable reedbeds, where reed grasses like Phragmites species and cattails ( Typha ) are present. They have also been found in rice fields, brackish water lagoons, and around fig trees ( Ficus verrucolosa ).

• Habitat Regions
• temperate temperate
• freshwater freshwater

• Aquatic Biomes
• lakes and ponds
• rivers and streams
• coastal coastal
• brackish water brackish water

• Wetlands
• swamp swamp

Physical Description

Purple heron wingspans range from 120 and 150 centimeters. The length of purple herons can range from 78 and 90 centimeters, while their body mass is between 499 grams and 1,361 grams. Purple heron sexes are alike.

The majority of adult purple heron bodies are a light colored grayish- purple with some variations of black, brown, and white. Black stripes run down each side of their brownish neck, from each eye and the top of the crown. Their crown is black, while the foreneck and chin are white. Ventral breasts are dark brown, which then transitions into black stomachs and tails. The upperwing feathers are light grey, while the underwing feathers are dark brown. They have chartreuse-colored eyes and yellow bills with a brown culmen and tip. The yellow bills are brighter during the breeding season.

Purple heron juveniles are brown with a small amount of black on the crown and nape. Juveniles lack the long black stripes along the neck. Purple heron chicks are brown with white-tipped upper parts.

Commonly confused with grey herons ( Ardea cinerea ), purple herons are slightly smaller, have darker feathers (e.g., darker grey backs), and appear to have a thinner build. Grey heron chicks are easier to distinguish from purple heron chicks because they are missing these white tips on their upper parts.

• Other Physical Features
• endothermic endothermic
• homoiothermic
• bilateral symmetry bilateral symmetry

• Sexual Dimorphism
• sexes alike

Reproduction

As a result of the widespread distribution of purple herons, the breeding season can vary. Breeding seasons occur in the western Palearctic from April to June, and during the rainy seasons in Africa. In northern India, breeding is June to October, while in southern India, breeding is November to March. These birds often form monogamous pairs, although it has been documented that purple heron males will raise a brood with two females simultaneously.

Nest construction depends on a collection of external factors, such as available materials in their location, water levels, or the presence of predators. More often than not, these nests will be found in reedbed or bulrush stands ( Scirpus or Typha ), with enough vegetative coverage to protect against ground predation. Surrounding water levels are usually between 0.4 to 1.5 meters deep. Although, when favorable reedbed criteria can't be met are reeds are missing entirely, these herons can nest in trees. These nests are usually assembled with stems and twigs, and take about a week to complete with continuous updates. Nests are 5-20 meters apart, 5 to 10 centimeters deep, 0.5-0.8 meters in diameter, and about 1 meter above water. If water levels rise or drop too suddenly, nests could be abandoned.

Purple herons find their mates by use of displays as documented by Tomlinson (1974). Brooding birds have been known to demonstrate a stretch display to an incoming bird, in which they stand vertically extended with collum (neck) plumage erect. Depending on male or female, they will produce a sound. They hold this position briefly and then completely retract, and the birds sink back into a crouching position within the nest. While sinking into crouch position, females will vocalize what is described as a ‘crak’ a few times, while males will clap their bill a total of three times as they crouch. They finish this display with their chest plumage upright and lower their head back down (Voisin, 1991).

Two other displays have been observed during mating behavior, allopreening and the greeting stance. Allopreening is exhibited by males after they have just finished their stretch displays. They will pick at their partners' chest and wings with their beak with chest plumage raised (Voisin, 1991). The greeting stance is an act in which males will first bow to their chosen females and after then standing, females will lay their head upon the chest of their male.

• Mating System
• monogamous monogamous
• polygynous polygynous

Purple herons breed annually. Breeding seasons occur in the western Palearctic from April to June, and during the rainy seasons of Africa. In northern India, breeding is June to October, while in southern India, breeding is November to March. The earliest eggs have been laid in April in temperate areas. European populations lay their eggs about three weeks later. Depending on location, and other ecological factors such as habitat disturbance, clutch sizes vary. On average, each nest can have 4.4 eggs per brood. Nest sizes can range between 2 and 8 eggs. Incubation periods are 20 to 30 days (average 26 days).

Chicks one day old weigh between 25 and 40 grams. At 40 to 50 days post-hatching, chicks have developed their juvenile plumage and are capable of flight. Around 56 days, they become independent. Both sexes are sexually mature at 2 years of age.

• Key Reproductive Features
• iteroparous iteroparous
• seasonal breeding seasonal breeding
• gonochoric/gonochoristic/dioecious (sexes separate)
• sexual sexual
• oviparous oviparous

Purple herons begin laying eggs typically late April through June in much of their range. Both parents contribute to nest-building in wetland habitats. Both parents brood the eggs, and take turns feeding the chicks through regurgitation. It takes about 10 days before the chicks can directly eat from their parent's beak. At 30 days old, chicks are able to leave the nest, but only during the day. At 40 to 50 days old, they are able to fly, and at 56 days, they are fully independent.

• Parental Investment
• altricial altricial
• male parental care male parental care
• female parental care female parental care
• pre-fertilization
  • provisioning
  • protecting
    • female
• pre-hatching/birth
  • provisioning
    • male
    • female
• pre-weaning/fledging
  • provisioning
    • male
    • female
  • protecting
    • male
    • female
• pre-independence
  • provisioning
    • male
    • female
  • protecting
    • male
    • female

Lifespan/Longevity

Purple herons can live up to a maximum of 25.4 years in the wild. In their first migration, more than one half (62%) of the juvenile population will not survive. For those that do survive their first year, the major cause of death is due to being hunted. They are not kept in captivity.

Behavior

Purple herons tend to be crepuscular. They begin and end the day by foraging individually. They sometimes forage diurnally if the area is well covered, and free from potential predators. They are a social species that breeds in pairs. Depending on geographic location, the amount of pairs can fall between single, double or more commonly triple digits. A few places in which breeding pairs are very low compared to most, are Czechoslovakia, Switzerland, and Rhine Valley in western Germany, with less than twenty pairs. In the Netherlands and Italy, they can form loose colonies ranging anywhere from around 400 to 1,000 pairs. Uncommonly, these groups can reach over a 1,000 pairs. In non-conventional areas, they have been found to nest in trees. A colony was found living in fig trees ( Ficus verrucolsa ) on a flooded island in Botswana. In the Cape Verde Islands, purple herons have adjusted to nesting in mango ( Mangifera ) trees.

Purple herons have a system of communication that incorporates the use of displays, calls, and postures. They demonstrate behavioral displays such as the 'head-scratch' in which they will extend their neck and raise a foot in order to scratch their head with their biggest toe. Another behavioral display is the 'gular-flutter' display. Here, the birds will leave their bill open slightly, while fluttering their gular region quickly; this has only been observed during warm weather. Other displays purple herons perform include greeting one another, showing aggression, and other breeding displays.

While populations in Africa and tropical-Asian areas do not migrate, other populations do. During migration which can begin between late August and early October, purple herons can fly 3,500-4,000 km in five to seven days. They use continuous active flapping diurnally and nocturnally, with brief stops. They usually will migrate in a group of 300 to 400 individuals.

Average flying speed in adult purple herons nocturnally ranged from 39.2-42.4 km/h, while average flying speed in adult purple herons diurnally was 39.3-44.7 km/h. In flight, their long necks curl into an S-shape.

• Key Behaviors
• arboreal arboreal
• flies
• diurnal diurnal
• crepuscular crepuscular
• motile motile
• migratory migratory
• sedentary sedentary
• solitary solitary
• social social
• colonial colonial

Home Range

Home ranges have not been reported for purple herons and territory sizes have not been quantified.

Communication and Perception

Purple herons have a variety of displays in which they use movement to communicate with one another. Aggressive displays include striking at the enemy with a squawk (Tomlinson, 1994) or attacking one another over a heronry. They have been shown to demonstrate alert postures, in which they stand motionless with eyes fixed on an invader. Their greeting and breeding displays are quite similar, if not the same. Purple herons will also exert a low guttural greeting call when returning to the nest, and a higher-pitched version when leaving (Voisin, 1991). Their calls are described as a croak and the sound most similar is "krek!" These calls have been characterized as similar to grey herons ( Ardea cinerea ).

• Communication Channels
• visual visual
• acoustic acoustic

• Perception Channels
• visual visual
• tactile tactile
• acoustic acoustic
• chemical chemical

Food Habits

Purple herons feed primarily at dusk and dawn, sometimes during the day. They tend to hunt alone in heavily vegetated shallow water. They hunt by standing still or wading very slowly, then rapidly striking prey and catching them within their bills. Their diet varies greatly, but is primarily fish-based. They catch small fish less than 15 cm long including pike ( Esox ), ten-spined sticklebacks ( Pygosteus pungitius ), carp ( Cyrprinus carpio ), gudgeon ( Gobio gobio ), and tench ( Tinca tinca ). They can also be insectivores that feed on beetles, locusts, dragonflies, and true bugs. They occasionally consume amphibians, such as Iberian ribbed newt ( Pleurodeles walti ), plus molluscs, and crustaceans. They also consume small mammals, such as water-voles ( Arvicola amphibius ).

• Primary Diet
• carnivore carnivore
  • piscivore piscivore
  • insectivore insectivore
  • eats non-insect arthropods
  • molluscivore molluscivore

• Animal Foods
• mammals
• amphibians
• reptiles
• fish
• insects
• terrestrial non-insect arthropods
• mollusks
• aquatic crustaceans

Predation

Documented avian predators of purple heron chicks and eggs include African marsh harriers ( Circus ranivorus ), and occasionally black crakes ( Limnocorax flavirostra ). Purple herons also are preyed on by mammalian predators such as clawless otters ( Aonyx capensis ), if water surrounding nests evaporates too quickly. Additional predators could include snakes, rats, and foxes.

During the nesting season, purple herons will adjust the height of their nest depending on the surrounding water levels. This strategy is designed to decrease chances of nest predation. Coloration of hatchlings and adults is cryptic.

• Anti-predator Adaptations
• cryptic cryptic

Ecosystem Roles

Purple herons can take in parasites after ingesting fish and other prey. These parasites include trematodes: Euclinostomum heterostomum , Bolbophorus confusas levantinas , and a relatively newly discovered species, Clinostomum golvani .

Economic Importance for Humans: Positive

Purple herons are beneficial to humans because they are useful bioindicators of pollution in aquatic systems. Eggs can be collected to tests for heavy metals such as selenium and copper, as well as other pollutants such as polychlorinated biphenyls (PCBs).

• Positive Impacts
• research and education

Economic Importance for Humans: Negative

There are no negative economic impacts of purple herons on humans.

Conservation Status

The IUCN Red List has listed the purple heron as a species of "Least concern." They are not listed on CITES or on any U.S. lists (because they are absent in the United States).

The global population of purple herons is estimated to be between 270,000 and 500,000 individuals. Threats to this species includes habitat loss (reedbed removal, conversion to agriculture) or alteration (e.g., drainage ditches that change the water supply to wetlands). Harvesting of reeds also is a threat.

This species is protected by the African-Eurasian Waterbird Agreement. This is a multi-international legally binding agreement that indicates the protective actions to be taken by individual countries that have joined. Conserving reed-bed habitats in their natural state appears to be the best route to maintaining populations of these herons.

Additional Links

Encyclopedia of Life

Contributors

Samantha Jones (author), Radford University, Alex Atwood (editor), Radford University, Karen Powers (editor), Radford University, Joshua Turner (editor), Radford University, Tanya Dewey (editor), University of Michigan-Ann Arbor.

References

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