Mixed-species foraging flock

A mixed-species feeding flock, also termed a mixed-species foraging flock, mixed hunting party or informally bird wave, is a flock of usually insectivorous birds of different species that join each other and move together while foraging.[1] These are different from feeding aggregations, which are congregations of several species of bird at areas of high food availability.

A mixed-species foraging flock typically has "nuclear" species that appear to be central to its formation and movement. Species that trail them are termed "attendants". Attendants tend to join the foraging flock only when the flock enters their territory.[2]

How such flocks are initiated is under investigation. In Sri Lanka, for example, vocal mimicry by the greater racket-tailed drongo might have a key role in the initiation of mixed-species foraging flocks,[3] while in parts of the American tropics noisy packs of foraging golden-crowned warblers might play the same role.[4] Forest structure is also believed to be an important factor deciding the propensity to form flocks.[5] In tropical forests, birds that glean food from foliage were the most abundant species in mixed-species flocks.[6]

A typical Neotropic mixed feeding flock moves through the forest at about 0.3 kilometers per hour (0.19 mph), with different species foraging in their preferred niches (on the ground, on trunks, in high or low foliage, etc.). Some species follow the flock all day, while others – such as the long-billed gnatwren[7] – join it only as long as it crosses their own territories.[8]

Costs and benefits

Several evolutionary mechanisms have been proposed to explain the formation of mixed-species flocks. These are usually described in terms of the costs and benefits to individuals. The key benefits that have been suggested are a reduction in predation risk through increased vigilance, that is, more eyes that can spot predators and raise an alarm and increased foraging efficiency.[9] Costs could include the risk of kleptoparasitism.[10]

In the Holarctic

In the North Temperate Zone, they are typically led by Paridae (tits and chickadees),[9] often joined by nuthatches,[11] treecreepers, woodpeckers (such as the downy woodpecker and lesser spotted woodpecker),[12] kinglets, and in North America Parulidae (New World "warblers")[13] – all insect-eating birds. This behavior is particularly common outside the breeding season.[9]

The advantages of this behavior are not certain, but evidence suggests that it confers some safety from predators, especially for the less watchful birds such as vireos (vireos) and woodpeckers, and also improves feeding efficiency, perhaps because arthropod prey that flee one bird may be caught by another.[9]

In the Neotropics

Insectivorous feeding flocks reach their fullest development in tropical forests, where they are a typical feature of bird life. In the Neotropics the leaders or "core" members may be black-throated shrike-tanagers in southern Mexico, or three-striped warblers elsewhere in Central America. In South America, core species may include antbirds such as Thamnomanes, antshrikes, Furnariidae (ovenbirds and woodcreepers) like the buff-fronted foliage-gleaner or the olivaceous woodcreeper, or Parulidae (New World "warblers") like the golden-crowned warblers.[4] In open cerrado habitat, it may be white-rumped or white-banded tanagers.[14] Core species often have striking plumage and calls that attract other birds; they are often also known to be very active sentinels, providing warning of would-be predators.[14][8]

But while such easy-to-locate bird species serve as a focal point for flock members, they do not necessarily initiate the flock. In one Neotropic mixed flock feeding on swarming termites, it was observed that buff-throated warbling finches were most conspicuous.[15] As this species is not an aerial insectivore, it is unlikely to have actually initiated the flock rather than happening across it and joining in. And while Basileuterus species are initiators as well as core species, mixed flocks of Tangara species – in particular red-necked, brassy-breasted, and green-headed tanagers – often initiate formation of a larger and more diverse feeding flock, of which they are then only a less significant component.[4]

Nine-primaried oscines make up much of almost every Neotropical mixed-species feeding flock. Namely, these birds are from families such as the cardinals, Parulidae (New World "warblers"), and in particular Emberizidae (American "sparrows") and Thraupidae (tanagers). Other members of a Neotropic mixed feeding flock may come from most of the local families of smaller diurnal insectivorous birds, and can also include woodpecker, toucans, and trogons. Most Furnariidae do not participate in mixed flocks, though there are exceptions such as Synallaxis spinetails and some species of the woodcreeper subfamily – e.g. those mentioned above or the lesser woodcreeper – are common or even "core" members. Among the tyrant flycatchers there are also some species joining mixed flocks on a somewhat regular basis, including the sepia-capped flycatcher, eared pygmy tyrant, white-throated spadebill, and Oustalet's tyrannulet.[4][14][15]

However, even of commonly participating families not all species join mixed flocks. There are genera such as Vireo in which some species do not join mixed flocks, while others (e.g., the red-eyed vireo) will even do so in their winter quarters.[4] Of the three subspecies groups of the yellow-rumped warbler, only one (Audubon's warbler) typically does. And while the importance of certain Thraupidae in initiating and keeping together mixed flocks has been mentioned already, for example the black-goggled tanager is an opportunistic feeder that will appear at but keep its distance from any disturbance – be it a mixed feeding flock, an army ant column or a group of monkeys – and pick off prey trying to flee.[4]

Gnateaters are notable for their absence from these flocks,[7] while swifts and swallows rarely join them, but will if there is for example an ant or termite swarm.[15][16][17][16] Cotingidae (cotingas) are mainly opportunistic associates which rarely join flocks for long if they do so at all; the same holds true for most Muscicapoidea (mockingbirds and relatives), though some thrushes may participate on more often.[4] And though most Tityridae rarely join mixed flocks, becards do so regularly.[4] Tapaculos are rarely seen with mixed flocks, though the collared crescentchest, doubtfully assigned to that family, may be a regular member.[14] Icteridae (grackles and relatives) are also not too often seen to take part in these assemblages, though caciques like the golden-winged or red-rumped cacique join mixed flocks on a somewhat more regular basis.[4] Cuculiformes (cuckoos and allies) are usually absent from mixed feeding flocks, but some – for example, the squirrel cuckoo – can be encountered not infrequently.[4]

Some species appear to prefer when certain others are present: Cyanolyca jays like to flock with unicolored jays and the emerald toucanets species complex. Many Icteridae associate only with related species, but the western subspecies of the yellow-backed oriole associates with jays and the band-backed wren.[18]

Other species participate to varying extents depending on location or altitude – presumably, the different species composition of mixed flocks at varying locations allows these irregular members more or less opportunity to get food. Such species include the grey-hooded flycatcher, or the plain antvireo and the red-crowned ant tanager which are often recorded in lowland flocks but rarely join them at least in some more montane regions.[4]

In the Old World tropics

The flocks in the Old World are often much more loosely bonded than in the Neotropics, many being only casual associations lasting the time the flock of core species spends in the attendants' territory. The more stable flocks are observed in tropical Asia, and especially Sri Lanka. Flocks there may number several hundred birds spending the entire day together, and an observer in the rain forest may see virtually no birds except when encountering a flock. For example, as a flock approaches in the Sinharaja Forest Reserve in Sri Lanka, the typical daytime quiet of the jungle is broken by the noisy calls of the orange-billed babbler and greater racket-tailed drongo, joined by species such as the ashy-headed laughingthrush, Kashmir flycatcher, and velvet-fronted nuthatch.

A mixed flock in the Cordillera Central of Luzon in the Philippines was mainly composed of bar-bellied cuckooshrikes, Philippine fairy-bluebirds, and violaceous crows. Luzon hornbills were also recorded as present. With the crows only joining later and the large hornbills probably only opportunistic attendants rather than core species, it is likely that this flock was started by one of the former species – probably the bold and vocal cuckoo-shrikes rather than the more retiring fairy-bluebirds, which are known to seek out such opportunities to forage.[19]

African rainforests also hold mixed-species flocks, the core species including bulbuls and sunbirds, and attendants being as diverse as the red-billed dwarf hornbill and the tit-hylia, the smallest bird of Africa. Drongos and paradise-flycatchers are sometimes described as the sentinels of the flock, but they are also known to steal prey from other flock members. Acanthizidae are typical core members in New Guinea and Australia; in Australia, fairy-wrens are also significant. The core species are joined by birds of other families such as minivets.[20]


  1. ^ Graves, G. R.; Gotelli, N. J. (15 February 1993). "Assembly of avian mixed-species flocks in Amazonia" (PDF). Proceedings of the National Academy of Sciences. 90 (4): 1388–1391. doi:10.1073/pnas.90.4.1388. ISSN 0027-8424. JSTOR 2361195. PMC 45878. PMID 8433996.
  2. ^ Faaborg, John; Chaplin, Susan B. (January 1988). Ornithology: an ecological approach. Englewood Cliffs, N.J: Prentice-Hall. pp. 219–221. ISBN 978-0-13-642877-0.
  3. ^ Goodale, Eben; Kotagama, Sarath W. (August 2006). "Vocal mimicry by a passerine bird attracts other species involved in mixed-species flocks" [Mixed flocks of birds in Atlantic Rain Forest in Serra de Paranapiacaba, southeastern Brazil] (PDF). Animal Behaviour (in Portuguese). 72 (2): 471–477. doi:10.1016/j.anbehav.2006.02.004. ISSN 0003-3472.
  4. ^ a b c d e f g h i j k Machado, C. G. (February 1999). "A composição dos bandos mistos de aves na Mata Atlântica da Serra de Paranapiacaba, no sudeste brasileiro". Revista Brasileira de Biologia [Brazilian Journal of Biology]. 59 (1). doi:10.1590/S0034-71081999000100010. ISSN 0034-7108.
  5. ^ Sridhar, Hari; Sankar, K. (January 2008). "Effects of Habitat Degradation on Mixed-Species Bird Flocks in Indian Rain Forests". Journal of Tropical Ecology. 24 (2): 135–147. doi:10.1017/S0266467408004823. ISSN 0266-4674. JSTOR 25172907. closed access
  6. ^ Thiollay, Jean-Marc (January 1999). "Frequency of Mixed Species Flocking in Tropical Forest Birds and Correlates of Predation Risk: An Intertropical Comparison". Journal of Avian Biology. 30 (3): 282–294. doi:10.2307/3677354. ISSN 0908-8857. JSTOR 3677354. closed access
  7. ^ a b Perrins 2003, "Gnateaters".
  8. ^ a b Perrins, 2003 & Antbirds.
  9. ^ a b c d Ehrlich, Paul R.; Dobkin, David S.; Wheye, Darryl. "Mixed-Species Flocking".
  10. ^ Chilton, Glen; Sealy, Spencer G. (January 1987). "Species Roles in Mixed-Species Feeding Flocks of Seabirds". Journal of Field Ornithology. 58 (4): 456–463. ISSN 0273-8570. JSTOR 4513268.
  11. ^ Perrins 2003, "Nuthatches".
  12. ^ Perrins 2003, "Woodpeckers".
  13. ^ Backhouse, Frances (January 2005). "Chapter 7: Relationships with Other Species". Woodpeckers of North America. Richmond Hill, Ontario: Firefly Books. ISBN 978-1-55407-046-6.
  14. ^ a b c d Ragusa-Netto, J. (August 2000). "Raptors and "campo-cerrado" bird mixed flock led by Cypsnagra Hirundinacea (Emberizidae:Thraupinae)". Revista Brasileira de Biologia. 60 (3): 461–7. doi:10.1590/S0034-71082000000300011. ISSN 0034-7108. PMID 11188872.
  15. ^ a b c Olson, Storrs L.; Alvarenga, Herculano M.F. (September 2006). "An extraordinary feeding assemblage of birds at a termite swarm in the Serra da Mantiqueira, São Paulo, Brazil" (PDF). Revista Brasileira de Ornitologia. 14 (3): 297–299.
  16. ^ a b Perrins 2003, "Swallows".
  17. ^ Perrins 2003, "Swifts".
  18. ^ Howell, Steve N. G.; Webb, Sophie (January 2010). A Guide to the Birds of Mexico and Northern Central America (Repr ed.). Oxford: Oxford Univ. Press. ISBN 978-0-19-854012-0.
  19. ^ Nuytemans, H. (January 1998). "Notes on Philippine birds: interesting records from northern Luzon and Batan Island" (PDF). Forktail. 14: 39–42.
  20. ^ Perrins 2003, "Cuckoo-shrikes".


  • Perrins, Christopher M., ed. (2003). Firefly Encyclopedia of Birds. Buffalo, N.Y: Firefly Books. ISBN 978-1-55297-777-4.
Agent-based model in biology

Agent-based models have many applications in biology, primarily due to the characteristics of the modeling method. Agent-based modeling is a rule-based, computational modeling methodology that focuses on rules and interactions among the individual components or the agents of the system. The goal of this modeling method is to generate populations of the system components of interest and simulate their interactions in a virtual world. Agent-based models start with rules for behavior and seek to reconstruct, through computational instantiation of those behavioral rules, the observed patterns of behavior. Several of the characteristics of agent-based models important to biological studies include:

Modular structure: The behavior of an agent-based model is defined by the rules of its agents. Existing agent rules can be modified or new agents can be added without having to modify the entire model.

Emergent properties: Through the use of the individual agents that interact locally with rules of behavior, agent-based models result in a synergy that leads to a higher level whole with much more intricate behavior than those of each individual agent.

Abstraction: Either by excluding non-essential details or when details are not available, agent-based models can be constructed in the absence of complete knowledge of the system under study. This allows the model to be as simple and verifiable as possible.

Stochasticity: Biological systems exhibit behavior that appears to be random. The probability of a particular behavior can be determined for a system as a whole and then be translated into rules for the individual agents.Before the agent-based model can be developed, one must choose the appropriate software or modeling toolkit to be used. Madey and Nikolai provide an extensive list of toolkits in their paper "Tools of the Trade: A Survey of Various Agent Based Modeling Platforms". The paper seeks to provide users with a method of choosing a suitable toolkit by examining five characteristics across the spectrum of toolkits: the programming language required to create the model, the required operating system, availability of user support, the software license type, and the intended toolkit domain. Some of the more commonly used toolkits include Swarm, NetLogo, RePast, and Mason. Listed below are summaries of several articles describing agent-based models that have been employed in biological studies. The summaries will provide a description of the problem space, an overview of the agent-based model and the agents involved, and a brief discussion of the model results.

Blue-faced honeyeater

The blue-faced honeyeater (Entomyzon cyanotis), also colloquially known as the bananabird, is a passerine bird of the honeyeater family, Meliphagidae. It is the only member of its genus, and it is most closely related to honeyeaters of the genus Melithreptus. Three subspecies are recognised. At around 29.5 cm (11.6 in) in length, the blue-faced species is large for a honeyeater. Its plumage is distinctive, with olive upperparts, white underparts, and a black head and throat with white nape and cheeks. Males and females are similar in external appearance. Adults have a blue area of bare skin on each side of the face readily distinguishing them from juveniles, which have yellow or green patches of bare skin.

Found in open woodland, parks and gardens, the blue-faced honeyeater is common in northern and eastern Australia and southern New Guinea. It appears to be sedentary in parts of its range and locally nomadic in other parts; however, the species has been little studied. Its diet is mostly composed of invertebrates, supplemented with nectar and fruit. They often take over and renovate old babbler nests, in which the female lays and incubates two or rarely three eggs.

Eurasian nuthatch

The Eurasian nuthatch or wood nuthatch (Sitta europaea) is a small passerine bird found throughout temperate Asia and in Europe, where its name is the nuthatch. Like other nuthatches, it is a short-tailed bird with a long bill, blue-grey upperparts and a black eye-stripe. It is a vocal bird with a repeated loud dwip call. There are more than 20 subspecies in three main groups; birds in the west of the range have orange-buff underparts and a white throat, those in Russia have whitish underparts, and those in the Far East have a similar appearance to European birds, but lack the white throat.

The preferred habitat is mature deciduous or mixed woodland with large, old trees, preferably oak. Pairs hold permanent territories, and nest in tree holes, usually old woodpecker nests, but sometimes natural cavities. If the entrance to the hole is too large, the female plasters it with mud to reduce its size, and often coats the inside of the cavity too. The 6–9 red-speckled white eggs are laid on a deep base of pine or other wood chips.

The Eurasian nuthatch eats mainly insects, particularly caterpillars and beetles, although in autumn and winter its diet is supplemented with nuts and seeds. The young are fed mainly on insects, with some seeds, food items mainly being found on tree trunks and large branches. The nuthatch can forage when descending trees head first, as well as when climbing. It readily visits bird tables, eating fatty man-made food items as well as seeds. It is an inveterate hoarder, storing food year-round. Its main natural predator is the Eurasian sparrowhawk.

Fragmentation of woodland can lead to local losses of breeding birds, but the species' range is still expanding. It has a large population and huge breeding area, and is therefore classified by the International Union for Conservation of Nature (IUCN) as being of least concern.

Feeding frenzy

In ecology, a feeding frenzy occurs when predators are overwhelmed by the amount of prey available. For example, a large school of fish can cause nearby sharks, such as the lemon shark, to enter into a feeding frenzy. This can cause the sharks to go wild, biting anything that moves, including each other or anything else within biting range. Another functional explanation for feeding frenzy is competition amongst predators. This term is most often used when referring to sharks or piranhas. It has also been used as a term within journalism.

Fish migration

Many types of fish migrate on a regular basis, on time scales ranging from daily to annually or longer, and over distances ranging from a few metres to thousands of kilometres.

Fish usually migrate to feed or to reproduce, but in other cases the reasons are unclear.

Migrations involve the fish moving from one part of a water body to another on a regular basis. Some particular types of migration are anadromous, in which adult fish live in the sea and migrate into fresh water to spawn, and catadromous, in which adult fish live in fresh water and migrate into salt water to spawn.

Marine forage fish often make large migrations between their spawning, feeding and nursery grounds. Movements are associated with ocean currents and with the availability of food in different areas at different times of year. The migratory movements may partly be linked to the fact that the fish cannot identify their own offspring and moving in this way prevents cannibalism. Some species have been described by the United Nations Convention on the Law of the Sea as highly migratory species. These are large pelagic fish that move in and out of the exclusive economic zones of different nations, and these are covered differently in the treaty from other fish.

Salmon and striped bass are well-known anadromous fish, and freshwater eels are catadromous fish that make large migrations. The bull shark is a euryhaline species that moves at will from fresh to salt water, and many marine fish make a diel vertical migration, rising to the surface to feed at night and sinking to lower layers of the ocean by day. Some fish such as tuna move to the north and south at different times of year following temperature gradients. The patterns of migration are of great interest to the fishing industry. Movements of fish in fresh water also occur; often the fish swim upriver to spawn, and these traditional movements are increasingly being disrupted by the building of dams.

Gleaning (birds)

Gleaning is a feeding strategy by birds in which they catch invertebrate prey, mainly arthropods, by plucking them from foliage or the ground, from crevices such as rock faces and under the eaves of houses, or even, as in the case of ticks and lice, from living animals. This behavior is contrasted with hawking insects from the air or chasing after moving insects such as ants. Gleaning, in birds, does not refer to foraging for seeds or fruit.

Gleaning is a common feeding strategy for some groups of birds, including nuthatches, tits (including chickadees), wrens, woodcreepers, treecreepers, Old World flycatchers, Tyrant flycatchers, babblers, Old World warblers, New World warblers, Vireos and some hummingbirds and cuckoos. Many birds make use of multiple feeding strategies, depending on the availability of different sources of food and opportunities of the moment.

Jungle babbler

The jungle babbler (Argya striata) is a member of the family Leiothrichidae found in the Indian subcontinent. They are gregarious birds that forage in small groups of six to ten birds, a habit that has given them the popular name of "Seven Sisters" in urban Northern India, and Saath bhai (seven brothers) in Bengali with cognates in other regional languages which also mean "seven brothers".The jungle babbler is a common resident breeding bird in most parts of the Indian subcontinent and is often seen in gardens within large cities as well as in forested areas. In the past, the orange-billed babbler, Turdoides rufescens, of Sri Lanka was considered to be a subspecies of jungle babbler, but has now been elevated to a species.


A pish is an imitated bird call (usually a scold or alarm call) used by birders and ornithologists to attract birds (generally passerines). The action of making the sound is known as pishing or spishing. This technique is used by scientists to increase the effectiveness of bird diversity surveys, and by birders to attract species that they might not otherwise see.

Pishing is used most effectively in the Holarctic, where it is thought to work due to its similarity to the scold calls of tits and chickadees (birds in the family Paridae). These scold calls, a form of mobbing behaviour, attract other birds which come in to establish the nature of the potential threat. Acoustical analysis of pishing calls and the mobbing calls of tits shows that they share a frequency metric not used by other birds. Not surprisingly, pishing has little effect on birds in those parts of the world without tits or chickadees.Another study noted that only passerine are attracted by pishing. Apart from the mobbing call hypothesis, it has also been suggested that pishing may be treated as an invitation to join a "mixed-species foraging flock" and birds do not themselves vocalize or show aggressive behaviour. The same study noted that pishing did not work in the old-world tropics and suggested that it may be due to the lower densities of migrants.Pishing has also been found to work effectively in Southern Africa (imitating a call of the rattling cisticola). It also works effectively in Australia where, despite the absence of any members of the Paridae, a number of passerine species can be attracted. Some birders in Australia use a variant of pishing called "squeaking" (making a kissing sound through pursed lips or against the back of one's hand) to which white-eared honeyeaters, several species of whistlers and grey fantails show an initial response and in turn attract other species.

Because pishing or squeaking disrupts the natural behaviour of a bird, birding organisations consider it unethical to make excessive use of this method of attracting birds. Such organisations recommend that, once the bird has been viewed, the birder cease pishing and allow the bird to return to its natural behaviour.

Biological swarming
Animal migration
Swarm algorithms
Collective motion
Swarm robotics
Related topics


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