Motion camouflage

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Principle of motion camouflage by mimicking the optic flow of the background. An attacker flies towards a target, choosing its path so that it remains on a line between target and a real point behind the attacker; this path differs from classical pursuit, and is often shorter (as illustrated here). The attacker looms larger as it closes on target, but does not otherwise appear to move. Motion Camouflage Principle.svg
Principle of motion camouflage by mimicking the optic flow of the background. An attacker flies towards a target, choosing its path so that it remains on a line between target and a real point behind the attacker; this path differs from classical pursuit, and is often shorter (as illustrated here). The attacker looms larger as it closes on target, but does not otherwise appear to move.
Animals such as frogs are very good at detecting motion, making motion camouflage a priority for predators. Red eyed tree frog edit2.jpg
Animals such as frogs are very good at detecting motion, making motion camouflage a priority for predators.

Motion camouflage is camouflage which provides a degree of concealment for a moving object, given that motion makes objects easy to detect however well their coloration matches their background or breaks up their outlines.

Contents

The principal form of motion camouflage, and the type generally meant by the term, involves an attacker's mimicking the optic flow of the background as seen by its target. This enables the attacker to approach the target while appearing to remain stationary from the target's perspective, unlike in classical pursuit (where the attacker moves straight towards the target at all times, and often appears to the target to move sideways). The attacker chooses its flight path so as to remain on the line between the target and some landmark point. The target therefore does not see the attacker move from the landmark point. The only visible evidence that the attacker is moving is its looming, the change in size as the attacker approaches.

Camouflage is sometimes facilitated by motion, as in the leafy sea dragon and some stick insects. These animals complement their passive camouflage by swaying like plants in the wind or ocean currents, delaying their recognition by predators.

First discovered in hoverflies in 1995, motion camouflage by minimising optic flow has been demonstrated in another insect order, dragonflies, as well as in two groups of vertebrates, falcons and echolocating bats. Since bats hunting at night cannot be using the strategy for camouflage, it has been named, describing its mechanism, as constant absolute target direction. This is an efficient homing strategy, and it has been suggested that anti-aircraft missiles could benefit from similar techniques.

Camouflage of approach motion

Many animals are highly sensitive to motion; for example, frogs readily detect small moving dark spots but ignore stationary ones. [1] Therefore, motion signals can be used to defeat camouflage. [2] Moving objects with disruptive camouflage patterns remain harder to identify than uncamouflaged objects, especially if other similar objects are nearby, even though they are detected, so motion does not completely 'break' camouflage. [3] All the same, the conspicuousness of motion raises the question of whether and how motion itself could be camouflaged. Several mechanisms are possible. [2]

Predators such as tigers stalk prey very slowly, to minimise motion cues. Hunting tiger edit1.jpg
Predators such as tigers stalk prey very slowly, to minimise motion cues.

Stealthy movements

One strategy is to minimise actual motion, as when predators such as tigers stalk prey by moving very slowly and stealthily. This strategy effectively avoids the need to camouflage motion. [2] [4]

Minimising motion signal

When movement is required, one strategy is to minimise the motion signal, for example by avoiding waving limbs about and by choosing patterns that do not cause flicker when seen by the prey from straight ahead. [2] Cuttlefish may be doing this with their active camouflage by choosing to form stripes at right angles to their front-back axis, minimising motion signals that would be given by occluding and displaying the pattern as they swim. [5]

Disrupting perception of motion

Disrupting the attacker's perception of the target's motion was one of the intended purposes of dazzle camouflage as used on ships in the First World War, though its effectiveness is disputed. This type of dazzle does not appear to be used by animals. [2]

Mimicking optic flow of background

The Australian emperor dragonfly mimics the optic flow of its background using real-point motion camouflage to enable it to approach rivals. Australian Emperor in flight.jpg
The Australian emperor dragonfly mimics the optic flow of its background using real-point motion camouflage to enable it to approach rivals.

Some animals mimic the optic flow of the background, so that the attacker does not appear to move when seen by the target. This is the main focus of work on motion camouflage, and is often treated as synonymous with it. [2] [6]

Pursuit strategies


An attacker can mimic the background's optic flow by choosing its flight path so as to remain on the line between the target and either some real landmark point, or a point at infinite distance (giving different pursuit algorithms). It therefore does not move from the landmark point as seen by the target, though it inevitably looms larger as it approaches. This is not the same as moving straight towards the target (classical pursuit): that results in visible sideways motion with a readily detectable difference in optic flow from the background. The strategy works whether the background is plain or textured. [6]

This motion camouflage strategy was discovered and modelled as algorithms in 1995 by M. V. Srinivasan and M. Davey while they were studying mating behaviour in hoverflies. The male hoverfly appeared to be using the tracking technique to approach prospective mates. [6] Motion camouflage has been observed in high-speed territorial battles between dragonflies, where males of the Australian emperor dragonfly, Hemianax papuensis were seen to choose their flight paths to appear stationary to their rivals in 6 of 15 encounters. They made use of both real-point and infinity-point strategies. [7] [8]

Falcons use infinite-point motion camouflage to close on their prey. Falcon 5 (5634955545).jpg
Falcons use infinite-point motion camouflage to close on their prey.

The strategy appears to work equally well in insects and in vertebrates. Simulations show that motion camouflage results in a more efficient pursuit path than classical pursuit (i.e. the motion camouflage path is shorter), whether the target flies in a straight line or chooses a chaotic path. Further, where classical pursuit requires the attacker to fly faster than the target, the motion camouflaged attacker can sometimes capture the target despite flying more slowly than it. [9] [2]

In sailing, it has long been known that if the bearing from the target to the pursuer remains constant, known as constant bearing, decreasing range (CBDR), equivalent to taking a fixed reference point at infinite distance, the two vessels are on a collision course, both travelling in straight lines. In a simulation, this is readily observed as the lines between the two remain parallel at all times. [9] [2]

Insect-hunting bats and some missiles follow an infinity-point pursuit path keeping parallel to the target ("Parallel navigation"), for its efficiency rather than for camouflage. Motion Camouflage Principle Parallel.svg
Insect-hunting bats and some missiles follow an infinity-point pursuit path keeping parallel to the target ("Parallel navigation"), for its efficiency rather than for camouflage.

Echolocating bats follow an infinity-point [2] path when hunting insects in the dark. This is not for camouflage but for the efficiency of the resulting path, so the strategy is generally called constant absolute target direction (CATD); [10] [11] [12] it is equivalent to CBDR but allowing for the target to manoeuvre erratically. [13]

A 2014 study of falcons of different species (gyrfalcon, saker falcon, and peregrine falcon) used video cameras mounted on their heads or backs to track their approaches to prey. Comparison of the observed paths with simulations of different pursuit strategies showed that these predatory birds used a motion camouflage path consistent with CATD. [13]

The missile guidance strategy of pure proportional navigation guidance (PPNG) closely resembles the CATD strategy used by bats. [14] The biologists Andrew Anderson and Peter McOwan have suggested that anti-aircraft missiles could exploit motion camouflage to reduce their chances of being detected. They tested their ideas on people playing a computerised war game. [15] The steering laws to achieve motion camouflage have been analysed mathematically. The resulting paths turn out to be extremely efficient, often better than classical pursuit. Motion camouflage pursuit may therefore be adopted both by predators and missile engineers (as "parallel navigation", for an infinity-point algorithm) for its performance advantages. [16] [17]

Attack strategies [13]
StrategyDescriptionCamouflage effectUsed by species
Classical pursuit (pursuit guidance)Move straight towards current position of target at all times (simplest strategy)None, target sees pursuer moving against backgroundHoney bees, flies, tiger beetles [13]
Real-point motion camouflageMove towards target keeping between it and a point near pursuer's start at all timesPursuer remains stationary against background (but looms larger)Dragonflies, hoverflies [13]
Infinity-point motion camouflage
(CATD, "Parallel navigation")		Move towards target keeping line to target parallel to line between pursuer's start and target at startPursuer remains at a constant direction in the skyDogs, humans, hoverflies, teleost fish, bats, falcons [13]

Camouflage by motion

Swaying: motion crypsis or masquerade

Swaying behaviour is practised by highly cryptic animals such as the leafy sea dragon, the stick insect Extatosoma tiaratum , and mantises. These animals resemble vegetation with their coloration, strikingly disruptive body outlines with leaflike appendages, and the ability to sway effectively like the plants that they mimic. E. tiaratum actively sways back and forth or side to side when disturbed or when there is a gust of wind, with a frequency distribution like foliage rustling in the wind. This behaviour may represent motion crypsis, preventing detection by predators, or motion masquerade, promoting misclassification (as something other than prey), or a combination of the two, and has accordingly also been described as a form of motion camouflage. [18] [19]

Related Research Articles

<span class="mw-page-title-main">Camouflage</span> Concealment in plain sight by any means, e.g. colour, pattern and shape

Camouflage is the use of any combination of materials, coloration, or illumination for concealment, either by making animals or objects hard to see, or by disguising them as something else. Examples include the leopard's spotted coat, the battledress of a modern soldier, and the leaf-mimic katydid's wings. A third approach, motion dazzle, confuses the observer with a conspicuous pattern, making the object visible but momentarily harder to locate, as well as making general aiming easier. The majority of camouflage methods aim for crypsis, often through a general resemblance to the background, high contrast disruptive coloration, eliminating shadow, and countershading. In the open ocean, where there is no background, the principal methods of camouflage are transparency, silvering, and countershading, while the ability to produce light is among other things used for counter-illumination on the undersides of cephalopods such as squid. Some animals, such as chameleons and octopuses, are capable of actively changing their skin pattern and colours, whether for camouflage or for signalling. It is possible that some plants use camouflage to evade being eaten by herbivores.

<span class="mw-page-title-main">Predation</span> Biological interaction

Predation is a biological interaction where one organism, the predator, kills and eats another organism, its prey. It is one of a family of common feeding behaviours that includes parasitism and micropredation and parasitoidism. It is distinct from scavenging on dead prey, though many predators also scavenge; it overlaps with herbivory, as seed predators and destructive frugivores are predators.

<span class="mw-page-title-main">Dragonfly</span> Predatory winged insects

A dragonfly is a flying insect belonging to the infraorder Anisoptera below the order Odonata. About 3,000 extant species of dragonflies are known. Most are tropical, with fewer species in temperate regions. Loss of wetland habitat threatens dragonfly populations around the world. Adult dragonflies are characterised by a pair of large, multifaceted, compound eyes, two pairs of strong, transparent wings, sometimes with coloured patches, and an elongated body. Many dragonflies have brilliant iridescent or metallic colours produced by structural coloration, making them conspicuous in flight. An adult dragonfly's compound eyes have nearly 24,000 ommatidia each.

<span class="mw-page-title-main">Animal echolocation</span> Method used by several animal species to determine location using sound

Echolocation, also called bio sonar, is a biological active sonar used by several animal groups, both in the air and underwater. Echolocating animals emit calls and listen to the echoes of those calls that return from various objects near them. They use these echoes to locate and identify the objects. Echolocation is used for navigation, foraging, and hunting prey.

<span class="mw-page-title-main">Horseshoe bat</span> Family of mammals

Horseshoe bats are bats in the family Rhinolophidae. In addition to the single living genus, Rhinolophus, which has about 106 species, the extinct genus Palaeonycteris has been recognized. Horseshoe bats are closely related to the Old World leaf-nosed bats, family Hipposideridae, which have sometimes been included in Rhinolophidae. The horseshoe bats are divided into six subgenera and many species groups. The most recent common ancestor of all horseshoe bats lived 34–40 million years ago, though it is unclear where the geographic roots of the family are, and attempts to determine its biogeography have been indecisive. Their taxonomy is complex, as genetic evidence shows the likely existence of many cryptic species, as well as species recognized as distinct that may have little genetic divergence from previously recognized taxa. They are found in the Old World, mostly in tropical or subtropical areas, including Africa, Asia, Europe, and Oceania.

<span class="mw-page-title-main">Batesian mimicry</span> Bluffing imitation of a strongly defended species

Batesian mimicry is a form of mimicry where a harmless species has evolved to imitate the warning signals of a harmful species directed at a predator of them both. It is named after the English naturalist Henry Walter Bates, who worked on butterflies in the rainforests of Brazil.

<span class="mw-page-title-main">Anti-predator adaptation</span> Defensive feature of prey for selective advantage

Anti-predator adaptations are mechanisms developed through evolution that assist prey organisms in their constant struggle against predators. Throughout the animal kingdom, adaptations have evolved for every stage of this struggle, namely by avoiding detection, warding off attack, fighting back, or escaping when caught.

<span class="mw-page-title-main">Crypsis</span> Aspect of animal behaviour and morphology

In ecology, crypsis is the ability of an animal or a plant to avoid observation or detection by other animals. It may be a predation strategy or an antipredator adaptation. Methods include camouflage, nocturnality, subterranean lifestyle and mimicry. Crypsis can involve visual, olfactory or auditory concealment. When it is visual, the term cryptic coloration, effectively a synonym for animal camouflage, is sometimes used, but many different methods of camouflage are employed by animals or plants.

<i>Hymenopus coronatus</i> Species of praying mantis

Hymenopus coronatus is a mantis from the tropical forests of Southeast Asia. It is known by various common names, including walking flower mantis, orchid-blossom mantis and (pink) orchid mantis. It is one of several species known as flower mantis, a reference to their unique physical form and behaviour, which often involves moving with a “swaying” motion, as if being “blown” in the breeze. Several species have evolved to mimic orchid flowers as a hunting and camouflaging strategy, “hiding” themselves in plain view and preying upon pollinating insects that visit the blooms. They are known to grab their prey with blinding speed.

<span class="mw-page-title-main">Ant mimicry</span> Animals that resemble ants

Ant mimicry or myrmecomorphy is mimicry of ants by other organisms; it has evolved over 70 times. Ants are abundant all over the world, and potential predators that rely on vision to identify their prey, such as birds and wasps, normally avoid them, because they are either unpalatable or aggressive. Some arthropods mimic ants to escape predation, while some predators of ants, especially spiders, mimic them anatomically and behaviourally in aggressive mimicry. Ant mimicry has existed almost as long as ants themselves; the earliest ant mimics in the fossil record appear in the mid-Cretaceous alongside the earliest ants.

<span class="mw-page-title-main">Long-legged bat</span> Species of bat

The long-legged bat is a member of the Phyllostomidae family in the order Chiroptera. Both males and females of this species are generally small, with wingspans reaching 80mm with an average weight ranging between 6 and 9 grams. The facial structure of these bats includes a shortened rostrum with a prominent noseleaf. The most defining feature of these bats however, is their long posterior limbs that extend farther than most Phyllostomidae bats. At the ends of these hind legs, the long-legged bat has abnormally large feet equipped with strong claws.

<span class="mw-page-title-main">Optokinetic response</span>

The optokinetic reflex (OKR), also referred to as the optokinetic response, or optokinetic nystagmus (OKN), is a compensatory reflex that supports visual image stabilization. The purpose of OKR is to prevent image blur on the retina that would otherwise occur when an animal moves its head or navigates through its environment. This is achieved by the reflexive movement of the eyes in the same direction as image motion, so as to minimize the relative motion of the visual scene on the eye. OKR is best evoked by slow, rotational motion, and operates in coordination with several complementary reflexes that also support image stabilization, including the vestibulo-ocular reflex (VOR).

<span class="mw-page-title-main">Ambush predator</span> Predator that sits and waits for prey to come to it

Ambush predators or sit-and-wait predators are carnivorous animals that capture their prey via stealth, luring or by strategies utilizing an element of surprise. Unlike pursuit predators, who chase to capture prey using sheer speed or endurance, ambush predators avoid fatigue by staying in concealment, waiting patiently for the prey to get near, before launching a sudden overwhelming attack that quickly incapacitates and captures the prey.

Ultrasound avoidance is an escape or avoidance reflex displayed by certain animal species that are preyed upon by echolocating predators. Ultrasound avoidance is known for several groups of insects that have independently evolved mechanisms for ultrasonic hearing. Insects have evolved a variety of ultrasound-sensitive ears based upon a vibrating tympanic membrane tuned to sense the bat's echolocating calls. The ultrasonic hearing is coupled to a motor response that causes evasion of the bat during flight.

<span class="mw-page-title-main">Australian emperor</span> Species of dragonfly

The Australian emperor dragonfly, also known as the yellow emperor dragonfly, scientific name Anax papuensis, is a species of dragonfly in the Aeshnidae family. It is black with yellow dots along its tail.

<span class="mw-page-title-main">Deimatic behaviour</span> Bluffing display of an animal used to startle or scare a predator

Deimatic behaviour or startle display means any pattern of bluffing behaviour in an animal that lacks strong defences, such as suddenly displaying conspicuous eyespots, to scare off or momentarily distract a predator, thus giving the prey animal an opportunity to escape. The term deimatic or dymantic originates from the Greek δειματόω (deimatóo), meaning "to frighten".

Echolocation systems of animals, like human radar systems, are susceptible to interference known as echolocation jamming or sonar jamming. Jamming occurs when non-target sounds interfere with target echoes. Jamming can be purposeful or inadvertent, and can be caused by the echolocation system itself, other echolocating animals, prey, or humans. Echolocating animals have evolved to minimize jamming, however; echolocation avoidance behaviors are not always successful.

<span class="mw-page-title-main">Pursuit predation</span> Hunting strategy by some predators

Pursuit predation is a form of predation in which predators actively give chase to their prey, either solitarily or as a group. It is an alternate predation strategy to ambush predation — pursuit predators rely on superior speed, endurance and/or teamwork to seize the prey, while ambush predators use concealment, luring, exploiting of surroundings and the element of surprise to capture the prey. While the two patterns of predation are not mutually exclusive, morphological differences in an organism's body plan can create an evolutionary bias favoring either type of predation.

Suzanne Amador Kane is a physicist and Professor of Physics and Astronomy at Haverford College. She is well known for her work utilizing video to understand the behavior of various species of birds.

References

  1. 1 2 Anstis, Stuart (1 June 2015). "Seeing Isn't Believing". The Scientist. Retrieved 28 April 2017.
  2. 1 2 3 4 5 6 7 8 9 Troscianko, Tom (2011). "Camouflage and Visual Perception". In Stevens, Martin; Merilaita, Sami (eds.). Animal Camouflage: Mechanisms and Function. Cambridge University Press. pp. 128–130. ISBN   978-1-139-49623-0.
  3. ↑ Hall, Joanna R.; Cuthill, Innes C.; Baddeley, Roland; Shohet, Adam J.; Scott-Samuel, Nicholas E. (7 May 2013). "Camouflage, detection and identification of moving targets". Proceedings of the Royal Society B. 280 (1578): 20130064. doi:10.1098/rspb.2013.0064. PMC   3619462 . PMID   23486439.
  4. ↑ Macdonald, David; Loveridge, Andrew (2010). The Biology and Conservation of Wild Felids. Oxford University Press. pp. 84–. ISBN   978-0-19-923444-8.
  5. ↑ Shohet, A.J.; Baddeley, R.J.; Anderson, J.C.; Kelman, E.J.; Osorio, D. (2006). "Cuttlefish responses to visual orientation of substrates, water flow and a model of motion camouflage" (PDF). Journal of Experimental Biology. 209 (23): 4717–4723. doi:10.1242/jeb.02580. PMID   17114404. S2CID   2485460.
  6. 1 2 3 Srinivasan, M. V. & Davey, M. (1995). "Strategies for active camouflage of motion". Proc. R. Soc. Lond. B. 259 (1354): 19–25. Bibcode:1995RSPSB.259...19S. doi:10.1098/rspb.1995.0004. S2CID   131341953.
  7. ↑ Hopkin, Michael (June 5, 2003). "Nature News". Dragonfly Flight Tricks the Eye. Nature.com. doi:10.1038/news030602-10 . Retrieved January 16, 2012.
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  10. ↑ Ghose, K'; Horiuchi, T.; Krishnaprasad, P. S.; Moss, C. (2006). "Echolocating bats use a nearly time-optimal strategy to intercept prey". PLOS Biology. 4 (5): 865–873. doi: 10.1371/journal.pbio.0040108 . PMC   1436025 . PMID   16605303.
  11. ↑ Reddy, P. V.; Justh, E. W.; Krishnaprasad, P. S. (2007). "Motion camouflage with sensorimotor delay" (PDF). 2007 46th IEEE Conference on Decision and Control. pp. 1660–1665. doi:10.1109/CDC.2007.4434522. ISBN   978-1-4244-1497-0. S2CID   1114039. Archived from the original (PDF) on 2018-01-14.
  12. ↑ Gonzalez-Bellido, Paloma T.; Fabian, Samuel T.; Nordström, Karin (December 2016). "Target detection in insects: optical, neural and behavioral optimizations". Current Opinion in Neurobiology. 41: 122–128. doi: 10.1016/j.conb.2016.09.001 . hdl: 1912/8647 . PMID   27662056. S2CID   3524650.
  13. 1 2 3 4 5 6 Amador Kane, Suzanne; Zamani, Marjon (2014). "Falcons pursue prey using visual motion cues: new perspectives from animal-borne cameras". Journal of Experimental Biology. 217 (2): 225–234. doi:10.1242/jeb.092403. PMC   3898623 . PMID   24431144.
  14. ↑ Justh, Eric W. (2010). Armstrong, Robert E.; Drapeau, Mark D.; Loeb, Cheryl A.; Valdes, James L. (eds.). Learning Unmanned Vehicle Control from Echolocating Bats. National Defense University Press. pp. 157–168. GGKEY:YX732WBJBQN.{{cite book}}: |work= ignored (help)
  15. ↑ Graham-Rowe, Duncan (28 June 2003). "Dragonfly trick makes missiles harder to dodge". New Scientist . Retrieved 27 April 2017.
  16. ↑ Justh, E. W.; Krishnaprasad, P. S. (2006). "Steering laws for motion camouflage". Proceedings of the Royal Society A. 462 (2076): 3629. arXiv: math/0508023 . Bibcode:2006RSPSA.462.3629J. CiteSeerX   10.1.1.236.1470 . doi:10.1098/rspa.2006.1742. S2CID   7992554.
  17. ↑ Carey, N. E.; Ford, J. J.; Chahl, J. S. (2004). "Biologically inspired guidance for motion camouflage". 5th Asian IEEE Control Conference. ISBN   0-7803-8873-9. S2CID   34907101.
  18. ↑ Bian, Xue; Elgar, Mark A.; Peters, Richard A. (2016). "The swaying behavior of Extatosoma tiaratum : motion camouflage in a stick insect?". Behavioral Ecology. 27 (1): 83–92. doi: 10.1093/beheco/arv125 .
  19. ↑ O'Dea, J. D. (1991). "Eine zusatzliche oder alternative Funktion der 'kryptischen' Schaukelbewegung bei Gottesanbeterinnen und Stabschrecken (Mantodea, Phasmatodea)". Entomologische Zeitschrift. 101 (1–2): 25–27.
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