Communal roosting is an animal behavior where a group of individuals, typically of the same species, congregate in an area for a few hours based on an external signal and will return to the same site with the reappearance of the signal. Environmental signals are often responsible for this grouping, including nightfall, high tide, or rainfall. The distinction between communal roosting and cooperative breeding is the absence of chicks in communal roosts. While communal roosting is generally observed in birds, the behavior has also been seen in bats, primates, and insects. The size of these roosts can measure in the thousands to millions of individuals, especially among avian species.
There are many benefits associated with communal roosting including: increased foraging ability, decreased thermoregulatory demands, decreased predation, and increased conspecific interactions. While there are many proposed evolutionary concepts for how communal roosting evolved, no specific hypothesis is currently supported by the scientific community as a whole.
One of the adaptive explanations for communal roosting is the hypothesis that individuals are benefited by the exchange of information at communal roosts. This idea is known as the information center hypothesis (ICH) and proposed by Peter Ward and Amotz Zahavi in 1973. It states that bird assemblages such as communal roosts act as information hubs for distributing knowledge about food source location. When food patch knowledge is unevenly distributed amongst certain flock members, the other "clueless" flock members can follow and join these knowledgeable members to find good feeding locations. To quote Ward and Zahavi on the evolutionary reasons as to how communal roosts came about, "...communal roosts, breeding colonies and certain other bird assemblages have been evolved primarily for the efficient exploitation of unevenly-distributed food sources by serving as ' information-centres.' "
The two strategies hypothesis was put forth by Patrick Weatherhead in 1983 as an alternative to the then popular information center hypothesis. This hypothesis proposes that different individuals join and participate in communal roosts for different reasons that are based primarily on their social status. Unlike the ICH, not all individuals will join a roost in order to increase their foraging capabilities. This hypothesis explains that while roosts initially evolved due to information sharing among older and more experienced foragers, this evolution was aided by the benefits that more experienced foragers gained due to the fact that as better foragers they acquired a status of high rank within the roost. As dominant individuals, they are able to obtain the safest roosts, typically those highest in the tree or closest to the center of the roost. In these roosts, the less dominant and unsuccessful foragers act as a physical predation buffer for the dominant individuals. This is similar to the selfish herd theory, which states that individuals within herds will utilize conspecifics as physical barriers from predation. The younger and less dominant individuals will still join the roost because they gain some safety from predation through the dilution effect, as well as the ability to learn from the more experienced foragers that are already in the roost.
Support for the two strategies hypothesis has been shown in studies of roosting rooks (Corvus frugilegus). A 1977 study of roosting rooks by Ian Swingland showed that an inherent hierarchy exists within rook communal roosts. In this hierarchy, the most dominant individuals have been shown to routinely occupy the roosts highest in the tree, and while they pay a cost (increased energy use to keep warm) they are safer from terrestrial predators. Despite this enforced hierarchy, lower ranking rooks remained with the roost, indicating that they still received some benefit from their participation in the roost. When weather conditions worsened, the more dominant rooks forced the younger and less dominant out of their roosts. Swingland proposed that the risk of predation at lower roosts was outweighed by the gains in reduced thermal demands. Similar support for the two strategies hypothesis has also been found in red-winged blackbird roosts. In this species the more dominant males will regularly inhabit roosts in thicker brush, where they are better hidden from predators than the less dominant individuals, that are forced to roost at the edge of the brush.
The TSH makes several assumptions that must be met in order for the theory to work. The first major assumption is that within communal roosts there are certain roosts that possess safer or more beneficial qualities than other roosts. The second assumption is that the more dominant individuals will be capable of securing these roosts, and finally dominance rank must be a reliable indicator of foraging ability.
Proposed by Heinz Richner and Phillip Heeb in 1996, the recruitment center hypothesis (RCH) explains the evolution of communal roosting as a result of group foraging. The RCH also explains behaviors seen at communal roosts such as: the passing of information, aerial displays, and the presence or lack of calls by leaders. This hypothesis assumes:
These factors decrease relative food competition since control over a food source by an individual is not correlated to the duration or richness of said source. The passing of information acts to create a foraging group. Group foraging decreases predation and increases relative feeding time at the cost of sharing a food source. The decrease in predation is due to the dilution factor and an early warning system created by having multiple animals alert. Increases in relative feeding are explained by decreasing time spent watching for predators and social learning. Recruiting new members to food patches benefits successful foragers by increasing relative numbers. With the addition of new members to a group the benefits of group foraging increase until the group size is larger than the food source is able to support. Less successful foragers benefit by gaining knowledge of where food sources are located. Aerial displays are used to recruit individuals to participate in group foraging. However, not all birds display since not all birds are members in a group or are part of a group that is seeking participants. In the presence of patchy resources, Richner and Heeb propose the simplest manner would be to form a communal roost and recruit participants there. In other words, recruitment to foraging groups explains the presence of these communal roosts.
Support for the RCH has been shown in ravens (Covus corax). Reviewing a previous study by John Marzluff, Bernd Heinrich, and Colleen Marzluff, Etienne Danchin and Heinz Richner demonstrate that the collected data proves the RCH instead of the Information Center Hypothesis supported by Marzluff, et al. Both knowledgeable and naïve ("clueless") birds are shown to make up the roosts and leave them at the same time, with the naïve birds being led to the food sources. Aerial demonstrations were shown to peak around the same time as the discovery of a new food source. These communities were made up of non-breeders which forage in patchily distributed food environments, following the assumptions made by Richner and Heeb. In 2014, Sarangi et. al. shown that the recruitment centre hypothesis did not hold in the study population of Common Mynas (Acridotheres tristis) and hence Common Myna roosts are not recruitment centres.
At this point in time there has been no additional scientific evidence excluding RCH or any evidence of overwhelming support. What is overlooked by RCH is that information may also be passed within the communal roost which increases and solidifies the community.
Birds in a communal roost can reduce the impact of wind and cold weather by sharing body heat through huddling, which reduces the overall energy demand of thermoregulation. A study by Guy Beauchamp explained that black-billed magpies (Pica hudsonia) often formed the largest roosts during the winter. The magpies tend to react very slowly at low body temperatures, leaving them vulnerable to predators. Communal roosting in this case would improve their reactivity by sharing body heat, allowing them to detect and respond to predators much more quickly.
A large roost with many members can visually detect predators easier, allowing individuals to respond and alert others quicker to threats. Individual risk is also lowered due to the dilution effect, which states that an individual in a large group will have a low probability of being preyed upon. Similar to the selfish-herd theory, communal roosts have demonstrated a hierarchy of sorts where older members and better foragers nest in the interior of the group, decreasing their exposure to predators. Younger birds and less able foragers located on the outskirts still demonstrate some safety from predation due to the dilution effect.
According to the ICH, successful foragers share knowledge of favorable foraging sites with unsuccessful foragers at a communal roost, making it energetically advantageous for individuals to communally roost and forage more easily. Additionally with a greater number of individuals at a roost, the searching range of a roost will increase and improve the probability of finding favorable foraging sites.
There are also potentially improved mating opportunities, as demonstrated by red-billed choughs (Pyrrhocorax pyrrhocorax), which have a portion of a communal roost dedicated to individuals that lack mates and territories.
It is costly for territorial species to physically travel to and from roosts, and in leaving their territories they open themselves up to takeovers. Communal roosts may draw the attention of potential predators, as the roost becomes audibly and visibly more conspicuous due to the number of members. There is also a decrease in the local food supply as a greater number of members results in competition for food. A large number of roost members can also increases the exposure to droppings, causing plumage to deteriorate and leaving birds vulnerable to dying from exposure as droppings reduce the ability of feathers to shed water.
Communal roosting has been observed in numerous avian species. As previously mentioned, rooks (Corvus frugilegus) are known to form large nocturnal roosts, these roosts can contain anywhere from a few hundred to over a thousand individuals. These roosts then disband at daybreak when the birds return to foraging activities. Studies have shown that communal roosting behavior is mediated by light intensity, which is correlated with sunset, where rooks will return to the roost when the ambient light has sufficiently dimmed.
Acorn woodpeckers (Melanerpes formicivorus) are known to form communal roosts during the winter months. In these roosts two to three individuals will share a cavity during the winter. Within these tree cavities woodpeckers share their body heat with each other and therefore decrease the thermoregulatory demands on the individuals within the roost. Small scale communal roosting during the winter months has also been observed in Green Woodhoopoes (Phoeniculus purpureus). Winter communal roosts in these species typically contain around five individuals.
Tree swallows (Tachycineta bicolor) located in southeastern Louisiana are known to form nocturnal communal roosts and have been shown to exhibit high roost fidelity, with individuals often returning to the same roost they had occupied on the previous night. Research has shown that swallows form communal roosts due to the combined factors of conspecific attraction, where individual swallows are likely to aggregate around other swallows of the same species, and roost fidelity. Tree swallows will form roosts numbering in hundreds or thousands of individuals.
Red-billed choughs (Pyrrhocorax pyrrhocorax) roost in what has been classified as either a main roost or a sub roost. Main roosts are constantly in use, whereas the sub roosts are used irregularly by individuals lacking both a mate and territory. These sub roosts are believed to help improve the ability of non-breeding choughs to find a mate and increase their territory ranges.
Interspecies roosts have been observed between different bird species. In San Blas, Mexico, the great egret (Ardea alba), the little blue heron (Egretta caerulea), the tricolored heron (Egretta tricolor), and the snowy egret (Egretta thula) are known to form large communal roosts. It has been shown that the snowy egret determines the general location of the roost due to the fact that the other three species rely on it for its abilities to find food sources. In these roosts there is often a hierarchical system, where the more dominant species (in this case the snowy egret) will typically occupy the more desirable higher perches. Interspecies roosts have also been observed among other avian species.
Communal roosting has also been well documented among insects, particularly butterflies. The passion-vine butterfly (Heliconius erato) is known to form nocturnal roosts, typically comprising four individuals. It is believed that these roosts deter potential predators due to the fact that predators attack roosts less often than they do individuals.
Communal roosting behavior has also been observed in the neotropical zebra longwing butterfly (Heliconius charitonius) in the La Cinchona region of Costa Rica. A study of this roost showed that individuals vary in their roost fidelity, and that they tend to form smaller sub roosts. The same study observed that in this region communal roosting can be mediated by heavy rainfall.
Communal roosting has also been observed in south Peruvian tiger beetles of the subfamily Cicindelidae. These species of tiger beetle have been observed to form communal roosts comprising anywhere from two to nine individuals at night and disbanding during the day. It is hypothesized that these beetles roost high in the treetops in order to avoid ground-based predators.
While there are few observations of communal roosting mammals, the trait has been seen in several species of bats. The little brown bat (Myotis lucifugus) is known to participate in communal roosts of up to thirty seven during cold nights in order to decrease thermoregulatory demands, with the roost disbanding at daybreak.
Several other species of bats, including the hoary bat (Lasiurus cinereus) and the big brown bat (Eptesicus fuscus) have also been observed to roost communally in maternal colonies in order to reduce the thermoregulatory demands on both the lactating mothers and juveniles.
The Arabian waxbill (Estrilda rufibarba) is a highly sociable species of estrildid finch native to Yemen and south-western Saudi Arabia. It has an estimated global extent of occurrence of 20,000 – 50,000 km2.Australo-Papuan babbler
The Pomatostomidae (Australo-Papuan or Australasian babblers, also known as pseudo-babblers) are small to medium-sized birds endemic to Australia-New Guinea. For many years, the Australo-Papuan babblers were classified, rather uncertainly, with the Old World babblers (Timaliidae), on the grounds of similar appearance and habits. More recent research, however, indicates that they are too basal to belong the Passerida – let alone the Sylvioidea where the Old World babblers are placed – and they are now classed as a separate family close to the Orthonychidae (logrunners). Five species in one genus are currently recognised, although the red-breasted subspecies rubeculus of the grey-crowned babbler may prove to be a separate species.Bronze mannikin
The bronze mannikin or bronze munia (Lonchura cucullata) is a small passerine (i.e. perching) bird of the Afrotropics. This very social estrildid finch is an uncommon to locally abundant bird in much of Africa south of the Sahara Desert, where it is resident, nomadic or irruptive in mesic savanna or forest margin habitats. It has an estimated global extent of occurrence of 8,100,000 km². It is the smallest and most widespread of four munia species on the African mainland, the other being black-and-white, red-backed and magpie mannikin. It co-occurs with the Madagascan mannikin on the Comoro Islands, and was introduced to Puerto Rico. Especially in the West Africa, it is considered a pest in grain and rice fields. It is locally trapped for the pet bird trade.Common myna
The common myna or Indian myna (Acridotheres tristis), sometimes spelled mynah, is a member of the family Sturnidae (starlings and mynas) native to Asia. An omnivorous open woodland bird with a strong territorial instinct, the myna has adapted extremely well to urban environments.
The range of the common myna is increasing at such a rapid rate that in 2000 the IUCN Species Survival Commission declared it one of the world's most invasive species and one of only three birds in the top 100 species that pose an impact to biodiversity, agriculture and human interests. In particular, the species poses a serious threat to the ecosystems of Australia where it was named "The Most Important Pest/Problem".Corvus
Corvus is a widely distributed genus of medium-sized to large birds in the family Corvidae. The genus includes species commonly known as crows, ravens, rooks and jackdaws; there is no consistent distinction between "crows" and "ravens", and these appellations have been assigned to different species chiefly on the basis of their size, crows generally being smaller than ravens.
Ranging in size from the relatively small pigeon-sized jackdaws (Eurasian and Daurian) to the common raven of the Holarctic region and thick-billed raven of the highlands of Ethiopia, the 45 or so members of this genus occur on all temperate continents except South America, and several islands. The crow genus makes up a third of the species in the family Corvidae. The members appear to have evolved in Asia from the corvid stock, which had evolved in Australia. The collective name for a group of crows is a "flock" or a "murder". The genus name is Latin for "raven".Recent research has found some crow species capable of not only tool use, but also tool construction. Crows are now considered to be among the world's most intelligent animals with an encephalization quotient equal to that of many non-human primates.Grey-breasted woodpecker
The grey-breasted woodpecker (Melanerpes hypopolius) is a species of bird in the family Picidae.
It is endemic to the interior of southwestern Mexico.Heliconius charithonia
Heliconius charithonia, the zebra longwing or zebra heliconian, is a species of butterfly belonging to the subfamily Heliconiinae of the family Nymphalidae. It was first described by Carl Linnaeus in his 1767 12th edition of Systema Naturae. The boldly striped black and white wing pattern is aposematic, warning off predators.
The species is distributed across South and Central America and as far north as southern Texas and peninsular Florida; there are migrations north into other American states in the warmer months.
Zebra longwing adults roost communally at night in groups of up to 60 adults for safety from predators. The adult butterflies are unusual in feeding on pollen as well as on nectar; the pollen enables them to synthesize cyanogenic glycosides that make their bodies toxic to potential predators. Caterpillars feed on various species of passionflower, evading the plants' defensive trichomes by biting them off or laying silk mats over them.
Mass spraying of naled has decimated the zebra longwing population in Miami-Dade County, Florida. There has been mass collapse of the colonies with impacts on the balance of the ecosystem. Further studies are needed to evaluate any potential for recolonization.Heliconius melpomene
Heliconius melpomene, the postman butterfly, common postman or simply postman, is a brightly colored butterfly found throughout Mexico and Central America. It was first described by Carl Linnaeus in his 1758 10th edition of Systema Naturae. Its coloration coevolved with a sister species H. erato as a warning to predators of its inedibility; this is an example of Müllerian mimicry. H. melpomene was one of the first butterfly species observed to forage for pollen, a behavior that is common in other groups but rare in butterflies. Because of the recent rapid evolutionary radiation of the genus Heliconius and overlapping of its habitat with other related species, H. melpomene has been the subject of extensive study on speciation and hybridization. These hybrids tend to have low fitness as they look different from the original species and no longer exhibit Müllerian mimicry.
H. melpomene possesses ultraviolet vision which enhances its ability to distinguish subtle differences between markings on the wings of other butterflies. This allows the butterfly to avoid mating with other species that share the same geographic range.Information centre hypothesis
The information centre hypothesis (ICH) is a theory that states bird species live in communal roosts primarily for the advantage of gaining information from others in the community regarding the location of unevenly distributed food resources. This hypothesis was first proposed by Peter Ward and Israeli biologist Amotz Zahavi (1973). They stated that birds join assemblages in order to gain information about food resources and increase foraging efficiency. Using this strategy would allow unsuccessful birds to return to the population and gain information, often by observing behavioural differences in successful birds. Following the exchange of knowledge, the unsuccessful individuals then follow those deemed successful back to the resource location.The hypothesis has been studied and experimentally supported in many different types of communally roosting birds, notably crows and vultures. This strategy is regarded as evolutionarily adaptive, because it would prevent the unsuccessful bird from having to start the search for food over in a random method. By the early 1980s, the information centre hypothesis was widely accepted and used to explain communal roosting behaviour, however this popularity also led to substantial criticism. One criticism of the theory is the multiple assumptions required to fulfill the criteria to support the hypothesis. Another criticism of the theory is its narrow scope, as it pertains strictly to food information sharing. Additional criticism questions whether the information centre hypothesis is an evolutionarily stable strategy.Intra-species recognition
Intra-species recognition is the recognition by a member of a species of a conspecific (another member of the same species). In many species, such recognition is necessary for procreation.
Different species may employ different methods, but all of them are based on one or more senses (after all, this is how the organism gathers information about the environment). The recognition may happen by chemical signature (smell), by having a distinctive shape or color (sight), by emitting certain sounds (hearing), or even by behaviour patterns. Often a combination of these is used.
Among human beings, the sense of sight is usually in charge of recognizing other members of the same species, with maybe the subconscious help of smell. In particular, the human brain has a disproportionate amount of processing power dedicated to finely analyze the features of a human face. This is why we are able to distinguish basically all six billions of human beings from each other (barring look-alikes), and a human being from a similar species like some anthropomorphic ape, with only a quick glance.
Intra-species recognition systems are often subtle. For example, ornithologists have great difficulty in distinguishing the chiffchaff from the willow warbler by eye, and there is no evidence that the birds themselves can do so other than by the different songs of the male. Sometimes, intra-species recognition is fallible: in many species of frog, the males are not uncommonly seen copulating with females of the wrong species or even with inanimate objects.
Heliconius charithonia displays intra-species recognition by roosting with conspecifics. They do this with the help of UV rhodopsins in the eye that help them distinguish between ultraviolet yellow pigments and regular yellow pigments. They have also been known to emit chemical cues in order to recognize members of their own species.Lonchura
Lonchura is a genus of the estrildid finch family, and includes munias (or minias), mannikins, and silverbills. They are resident breeding birds in Africa and in South Asia from India, Bangladesh, Sri Lanka east to Indonesia, Papua New Guinea, and the Philippines. Two of the approximately thirty-seven species are also native to Australia. The name mannikin is from Middle Dutch mannekijn 'little man' (also the source of the different bird name manakin).Some of the Lonchura species were formerly placed in Spermestes. Others have been placed in a genus of their own, Euodice.Long-eared owl
The long-eared owl (Asio otus), also known as the northern long-eared owl, is a species of owl which breeds in Europe, Asia, and North America. This species is a part of the larger grouping of owls known as typical owls, family Strigidae, which contains most species of owl. The other grouping of owls are the barn owls, family Tytonidae.
The scientific name is from Latin. The genus name Asio is a type of eared owl, and otus also refers to a small eared owl.Outline of birds
The following outline is provided as an overview of and topical guide to birds:
Birds (class Aves) – winged, bipedal, endothermic (warm-blooded), egg-laying, vertebrate animals. There are around 10,000 living species, making them the most varied of tetrapod vertebrates. They inhabit ecosystems across the globe, from the Arctic to the Antarctic. Extant birds range in size from the 5 cm (2 in) bee hummingbird to the 2.75 m (9 ft) ostrich.Palawan hornbill
The Palawan hornbill (Anthracoceros marchei), known as Talusi in the Philippine language Cuyunon, is a largish (approximately 70 centimetres (28 in) long, weighing 750 grams (26 oz), more than 92% of bird species) forest-dwelling bird. Its plumage is predominantly black, with a white tail, a dark green gloss on its upper parts and a large creamy-white beak with a casque typical of the hornbill family. It emits loud calls which can be transcribed as kaaww and kreik-kreik.
Nine species of hornbill are found in the Philippines, and the Palawan hornbill is endemic to Palawan island, but has also been recorded on the nearby islands of Balabac, Busuanga, Calauit, Culion and Coron. Most visiting birdwatchers travel to St Paul's National Park, Palawan, to see this bird, but it is now uncommon. It acts as a bio-indicator due to its sensitivity to environmental changes. It is officially classified as "vulnerable", and its numbers have reduced by at least 20% in the last 10 years due to habitat destruction, hunting for food, and the live bird trade.
The Palawan hornbill consumes mostly fruit, but also occasional insects and vertebrates. Due to its large size and home range, it is an important vector of seed dispersal for large-seeded trees. Many ground-dwelling seed-eating mammals live beneath such trees, and in areas where hornbills have become rare,
consume such a large percentage of the fallen seeds that they threaten the trees' survival.It is usually seen in pairs or small noisy family groups, and it has a communal roosting site. It is most usually observed in fruiting trees at the forest edge, but also feeds on insects and small reptiles.Passenger pigeon
The passenger pigeon or wild pigeon (Ectopistes migratorius) is an extinct species of pigeon that was endemic to North America. Its common name is derived from the French word passager, meaning "passing by", due to the migratory habits of the species. The scientific name also refers to its migratory characteristics. The morphologically similar mourning dove (Zenaida macroura) was long thought to be its closest relative, and the two were at times confused, but genetic analysis has shown that the genus Patagioenas is more closely related to it than the Zenaida doves.
The passenger pigeon was sexually dimorphic in size and coloration. The male was 390 to 410 mm (15.4 to 16.1 in) in length, mainly gray on the upperparts, lighter on the underparts, with iridescent bronze feathers on the neck, and black spots on the wings. The female was 380 to 400 mm (15.0 to 15.7 in), and was duller and browner than the male overall. The juvenile was similar to the female, but without iridescence. It mainly inhabited the deciduous forests of eastern North America and was also recorded elsewhere, but bred primarily around the Great Lakes. The pigeon migrated in enormous flocks, constantly searching for food, shelter, and breeding grounds, and was once the most abundant bird in North America, numbering around 3 billion, and possibly up to 5 billion, “at the time of the discovery of America,” according to A. W. Schorger.Though one genetic study concluded that the bird was not always that abundant, and that the population size fluctuated dramatically over time, a more recent study found evidence that this was not the correct interpretation of the genetic data, and instead concluded that the passenger pigeon population size had been stable for at least 20,000 years prior to "its 19th-century decline and eventual extinction." A very fast flyer, the passenger pigeon could reach a speed of 100 km/h (62 mph). The bird fed mainly on mast, and also fruits and invertebrates. It practiced communal roosting and communal breeding, and its extreme gregariousness may be linked with searching for food and predator satiation.
Passenger pigeons were hunted by Native Americans, but hunting intensified after the arrival of Europeans, particularly in the 19th century. Pigeon meat was commercialized as cheap food, resulting in hunting on a massive scale for many decades. There were several other factors contributing to the decline and subsequent extinction of the species, including shrinking of the large breeding populations necessary for preservation of the species and widespread deforestation, which destroyed its habitat. A slow decline between about 1800 and 1870 was followed by a rapid decline between 1870 and 1890. The last confirmed wild bird is thought to have been shot in 1901. The last captive birds were divided in three groups around the turn of the 20th century, some of which were photographed alive. Martha, thought to be the last passenger pigeon, died on September 1, 1914, at the Cincinnati Zoo. The eradication of this species is a notable example of anthropogenic extinction.Puerto Rican tanager
The Puerto Rican tanager (Nesospingus speculiferus) is a small passerine bird endemic to the archipelago of Puerto Rico. It is the only member of the genus Nesospingus and has historically been placed in the tanager family, but recent studies indicate another placement. The Puerto Rican tanager is known to locals as: "Llorosa," which means "cryer".Red-whiskered bulbul
The red-whiskered bulbul (Pycnonotus jocosus), or crested bulbul, is a passerine bird found in Asia. It is a member of the bulbul family. It is a resident frugivore found mainly in tropical Asia. It has been introduced in many tropical areas of the world where populations have established themselves. It feeds on fruits and small insects. Red-whiskered bulbuls perch conspicuously on trees and have a loud three or four note call. They are very common in hill forests and urban gardens within its range.Torresian crow
The Torresian crow (Corvus orru), also called the Australian crow or Papuan crow, is a passerine bird in the crow family native to the north and west of Australia and nearby islands in Indonesia and Papua New Guinea. The species has a black plumage, beak and mouth with white irises. The base of the feathers on the head and neck are white. The Torresian crow is slightly larger with a more robust bill than the morphologically similar little crow.Treecreeper
The treecreepers are a family, Certhiidae, of small passerine birds, widespread in wooded regions of the Northern Hemisphere and sub-Saharan Africa. The family contains ten species in two genera, Certhia and Salpornis. Their plumage is dull-coloured, and as their name implies, they climb over the surface of trees in search of food.