Colour matters

Colour change is a surprisingly widespread feature in the animal kingdom. Rapid colour change occurs in both invertebrates and vertebrates. The feature has been observed in crustaceans, insects, cephalopods, amphibians, reptiles and fish.

There are two main methods for changing colour: morphological and physiological colour change. Morphological colour change is based on changes in the number and quality of pigmentophores, whereas physiological colour change is based on changes in the number of organella within the pigmentophores. Melanophores are the most common pigmentophores to have melanosomes. Physiological colour change is much faster than morphological colour change. It can happen in microseconds. Physiological colour change is regulated by the neuromuscular system in cephalopods and by the neuroendocrine system in other classes. Environmental factors, such as background, lighting conditions, temperature and moisture, along with behaviour and stress can trigger physiological colour change.

Animals capable of changing colour usually have more than one colour-change strategy. Environment, the number of predators, predator species and the presence of individuals of the same species influence the colour-change strategy. For example, the daisy parrotfish (or bullethead parrotfish, Chlorurus sordidus) has three different colourations: individuals have stripes, are all black or have an eye-dot on the tail. The purpose of the eye-dot is to frighten predators, whereas the all-black daisy parrotfish tries to blend in with its background and the striped daisy parrotfish tries to bluff or dazzle its predators. The occurrence of these colourations is influenced by environmental background, the body size of the daisy parrotfish and its social relationships. On the other hand, the common cuttlefish (Sepia officinalis) chooses its strategy by whether a predator hunts using vision or chemical signals (watch how the common cuttlefish changes its colour). Chameleons (Chamaeleonidae), however, change their colour according to the environmental background rather than to mimic or to frighten.

The common octopus (Octopus vulgaris) can change its colour. © Sari Holopainen

Temperature affects the melanocyte-stimulating hormone (MSH) in many colour-changing animals such as fish, amphibians, reptiles and crustaceans. MSH is in charge of dispersing melanin. Changing to a dark or light colour helps an animal to either reflect or absorb heat. On the other hand, changing colour can concurrently predispose the animal to predation, because the animal is unable to blend in with its environment. The colour change of over 25 desert reptile species has been proven to depend on both environmental temperature and body temperature regulation. When it gets very warm (over +40°C) reptiles change to a lighter colour despite their background being somewhat dark. The reptiles usually still escape from predation because predators are inactive at such high temperatures. In proportion, when it gets cooler reptiles become darker than their environment, especially if they are near to cover.

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Hunters and conservationists – with shared cause

Do hunters conserve nature? This seemingly controversial issue seems to be a source of never-ending debate. I recently found a text discussing this issue, published in the “Finnish Nature” (Suomen Luonto) magazine as early as 1944. While conservationists and hunters may sometimes be in direct conflict, some shared targets were recognized already in 1944.

Extensive red fox hunting makes it possible for the rare arctic fox to breed successfully in Sweden and Norway. Red fox in an arctic fox habitat in Varanger Peninsula, northern Norway. © Sari Holopainen

Extensive red fox hunting makes it possible for the rare arctic fox to breed successfully in Sweden and Norway. Red fox in an arctic fox habitat in Varanger Peninsula, northern Norway. © Sari Holopainen

O. Hytönen (1944) raised the very same observations that are still apparent. Although hunters kill animals, prey animal populations should not be eradicated by responsible hunting practices. Some hunting actions are straightly connected to nature conservation, such as feeding animals during harsh winters, habitat management and predator control. Currently discussed effect of trophy hunting as an important conservation tool in development countries is an example of an indirect connection: by paying for hunting permits hunters help to maintain local animal diversity. As noted in a recently published paper, banning of trophy hunting can lead to exacerbating biodiversity loss.

In 1953 “Finnish Nature” (Suomen Luonto) published another text on the subject, this time written by G. Bergman. Bergman wrote that the relationships between hunters and conservationists has not always been smooth in Finland, or in other Nordic countries, while no benefits could be gained from these conflicts. Bergman noted that modern game management has several shared principles with nature conservation. He also pointed out that nature conservation and hunting have successfully been managed together in the US. As during Bergman’s times, Europe is still somehow on separate paths, and the situation has become particularly inflamed in some countries. Ironically, Bergman wrote that if we refuse to understand the interests of others, nature conservation aims may be disturbed.

The good old American way

What were the good manners already mentioned by Bergman in America? Maybe he meant the Federal Duck Stamp system established already in 1934. All US hunters must buy a Duck Stamp on a yearly basis, however, whoever can get one. With this small cost the buyers contribute to bird habitat conservation. The US Fish and Wildlife Service advertises that the stamp is “among the most successful conservation tools ever created to protect habitat for birds and other wildlife”. About 1 500 000 stamps are bought yearly, and 98% of the profits are given to the National Wildlife Refuge System for wetland conservation.

Coldwater River National Wildlife Refuge in Mississippi provides great circumstances for wintering ducks. The park is protected, but bird watching is aloud in some parts of the park. Duck hunting is possible outside the park in private lands. © Sari Holopainen

Coldwater River National Wildlife Refuge in Mississippi provides great circumstances for wintering ducks. The park is protected, but bird watching is aloud in some parts of the park. Duck hunting is possible outside the park in private lands. © Sari Holopainen

Another traditional American actor smoothly combining conservation and hunting is Ducks Unlimited (DU), founded by a group of hunters in 1937. DU targets habitat conservation, and is now claimed to be the world’s largest and most effective private waterfowl and wetlands conservation organization according to their website. Most DU members are still hunters.

The land of a thousand lakes

Wetlands have been destroyed for a long time due to differing human interests, also in Finland. Some areas have been lost altogether, while some have lost their value due to e.g. vegetation overgrowth. We still have many lakes left, but shallow eutrophic lakes – the waterbird lakes – are the ones that have been lost most often. Hunters are a group with an interest to construct and restore wetlands. According to a report by the Finnish Wildlife Agency, hunters have constructed or restored about 2 000 wetlands during the past decades. In addition to benefitting game animals, the entire ecosystem benefits. Wetlands also offer several other ecosystem services, including water purification and erosion control.

Many wetlands have been established in Finland to support game animals. Saarikko-wetland in southern Finland is a small, yet very productive duck habitat constructed by the REAH-project (active management of game animal habitats). © Sari Holopainen

Many wetlands have been established in Finland to support game animals. Saarikko-wetland in southern Finland is a small, yet very productive duck habitat constructed by the REAH-project (active management of game animal habitats). © Sari Holopainen

Methods matter

Sometimes hunting itself supports animal populations. For example, hunters can help to maintain animal communities through ecosystem engineering pushed by hunting and the co-evolution of animals and humans. In 2013 a scientific paper showed that in Australia Aboriginal hunting was one of the cornerstones supporting monitor lizard populations. Monitor lizards occur most densely in areas where they are hunted, because of the hunting method used; the burning method creates a patchy mosaic of regrowth in the landscape. In areas with no hunters, occasional lightning strikes burn land in a more homogenous way, and thus also lizards are scarcer. The same practice might also benefit several other desert species. However, in many cases Aboriginals have lost their traditional hunting possibilities, and the loss of these traditional practices sustaining habitats might have contributed to decreasing populations of several desert animal species.

While the debate between hunting and nature conservation has already lasted a long time, and is still on-going, common targets have been raised throughout the process by cooperative actors of both sides. There has always been, and currently still are, differing hunting methods for concerning conservational effects, but it is self-evident that all these practices are not against conservation targets.

Read more:

Enrico Di Minin, Nigel Leader-Williams & Corey J.A. Bradshaw: Banning Trophy Hunting Will Exacerbate Biodiversity Loss. 2015. Trends in Ecology & Evolution. Online.

Connecting Aboriginal Land Use Management Strategies, Mammal Extinction Rates and Shifts in Fire Regimes in a Changing Climate: An Interdisciplinary Approach to Inform Conservation Strategies for Threatened Species in the Australian Western Desert

An interdisciplinary approach to understanding the role of anthropogenic fire in the desert grasslands of Australia

Amphibious sea snakes – torn in between

When I attended the International Wildlife Management Congress (5th IWMC) in Sapporo Japan, I was blown away with a very interesting group of sea snakes: the amphibious sea snakes (Laticaudinae), also known as sea kraits. They possess traits of both land and sea snakes. They are kind of torn between living on land or in the ocean. Their evolution has led to characteristics that enable them to live in both environments, at least for certain periods at a time. But these multiple skills come with a trade-off. For example the locomotion ability in aquatic environments may reduce their terrestrial locomotor ability and vice versa. Even though terrestrial crawling and aquatic swimming are superficially similar activities in snakes, they need different substrates to produce the motion. In general sea kraits move over twice as fast in water than on land.

The ability to move on land is based on both their ventral scales, which are wide just as with land snakes, and their poorly developed tail fins. Sea kraits also use land as their freshwater source. Even though they have a salt gland to excrete the excess salt, they also have to drink freshwater to obtain a proper water balance within their bodies. The freshwater resources that sea kraits use are rainwater, estuaries and sea springs. Estuaries are used by all species, not just to drink freshwater, but also to hide.

The reproduction of amphibious sea snakes differs from true sea snakes (Hydrophinae). Firstly, they are oviparous, whereas true sea snakes are viviparous. Viviparous means that snakes give birth to live young. Oviparous on the contrary means the animal lays eggs and the offspring hatch from them. Sea kraits return to land to mate and lay eggs. The eggs are laid in nests fulfilling certain specific condition.

Sea kraits have lungs for breathing. They therefore need to surface every 15 minutes on average to breathe. The breaking of the surface may take only a split second while a sea krait takes a breath of air and dives again. Most of their time they spend at sea in shallow tropical reefs, which are threatened in several ways. Agricultural and urban runoff, in addition to both organic and inorganic pollution are one of the main threats to shoreline tropical reefs. Many sea krait species are considered vulnerable or nearly threatened. Hopefully we will be able to conserve these interesting and mesmerizing creatures of the oceans before it’s too late.