Corvids, the black health police

Biologist Gela Preisfeld on our clever, black songbirds

If you go for a walk in the Scharpenacken recreation area in Wuppertal, you will notice the many crows and jackdaws that flock to the fences and meadows. Wuppertal biologist Gela Preisfeld knows the history of these mostly black songbirds, which are both hated and adored, and their importance for the ecosystem.

Recent dinosaurs

"Birds are the recent dinosaurs, they are the ones that have survived," says Gela Preisfeld, Professor of Zoology and Didactics of Biology at the University of Wuppertal, quoting a sentence that emphasises birds as a very special group of vertebrates: "There is no recent bird (living in modern times, editor's note) without feathers and there is no animal that has feathers and is not a bird." In terms of evolutionary biology, they are closer to humans as an ancestral community with reptiles than amphibians, for example. "They evolved from a very specific line of dinosaurs, the theropods. These also had feathers and were already equally warm, i.e. homoiothermic. Birds are the only animal group apart from us mammals that are homothermic. All other animals are alternately warm, i.e. they cannot regulate their internal temperature independently of the external temperature. Birds, like their ancestors, already have these more mobile arms and hands, which, together with the development of feathers, mean that they can also use them as wings. Although theropods were unable to fly - some may have been able to glide - some evolved into birds. In other words, birds are living dinosaurs!" In this context, it is also interesting to note that Archaeopteryx, the best-known so-called prehistoric bird, was not huge, but merely the size of a pigeon.

Home of the corvids

Corvids originally come from dense forests in the tropical forests of Southeast Asia and have now conquered almost all habitats. "The dividing line between the faunal areas of the Orientalis and Australis is the so-called Wallace Line (the Wallace Line is the biogeographical line that indicates the furthest spread of Australian fauna in the Malay Archipelago, editor's note)," explains Preisfeld, "this dividing line represents an incredibly species-rich area with high biodiversity (a hotspot), which then splits somewhat to the north-east and south-west. To the east of it, the corvids that exist in our country do not occur apart from crows and ravens, but apart from South America, where the blue ravens occupy the ecological niche, they have established themselves worldwide."

According to the biologist, there are currently around 11,000 species of birds, of which 5,000 are songbirds alone. "We have around 120 corvids. From the genus Corvus, which includes ravens and crows, there are nine. These are rooks, hooded crows and their hybrids, ravens, choughs, jackdaws, jays, nutcrackers, magpies and the largest of these species at 75 cm, the playful ravens."

Corvids belong to the songbirds

"The songbirds are a large group within the Neognathae (New-jawed birds) and produce their sounds in the syrinx, the lower larynx," explains Preisfeld. "We humans have our vocal cords in the larynx, but in birds the syrinx is lower down, at the point where the trachea (windpipe) splits into the bronchial branches. Small membranes are located there in pairs to the right and left. When the bird inhales and stretches, the muscles are tensed and when it exhales, the membranes vibrate and the sound is produced." Songbirds have up to nine membranes, which can be tensed independently of each other. This also enables them to sing in several voices. Now, the layman would not necessarily associate the cawing and screaming of corvids with the ability to sing, but with birds it is mostly about the different calls that they can produce vocally. The biologist explains: "Around 80 different calls are known for the common raven. As a rule, these are alarm calls for the others. But they also have so-called subsongs, something like sub-songs. These are more like the babbling of small children. However, these subsongs also enable them to imitate other animal sounds, ringtones or human voices. It is assumed that the subsongs are intended to train the entire vocal production apparatus. It is therefore mainly young animals that do this. In contrast to the subsongs, the calls of animals are structured and have a meaning. In ornithology, these screaming sounds that warn of enemies are referred to as 'hating', and this ability is very pronounced in corvids, i.e. they scream and also fly in the direction of the danger, i.e. they can combine both actions. This is an incredible feat of intelligence."

Tumultuous gallows birds or wise oracles

In earlier times, ravens were often referred to as witchcraft and gallows birds, which often symbolised a bad omen. This was due to the fact that they were black to begin with and were often associated with the negative, explains Preisfeld, but the 'gallows bird' is actually quite simple to explain: "They are also scavengers. When hanged people were dangling from the gallows for a long time, they ate the flesh. They also ate the flesh of the dead in times of serious illness. In earlier times, when corpses lay on a battlefield, ravens would come and eat the dead. This gave them an important ecological function - similar to the gravediggers - because that's what they do where animals die." On the other hand, they are also described as wise and were once thought to be able to predict the future. That's why women who were labelled as witches often had ravens or crows with them. "Even Aristotle recognised the intelligence of animals and wrote about it. If you look at other cultures, such as North American indigenous people, you can see that they are worshipped there as god-like creatures."

They also used to be popular in villages and towns because they 'tidied up'. "Today, we no longer need that and find them more of a nuisance."

Prejudices are often traditional knowledge

Until 1940, corvids were hunted almost to extinction, but are now a protected species, which annoys many farmers. "Farmers are of the opinion that they cause major damage to crops and crops and disturb the population of small game and smaller birds. There is also the opinion that they reproduce in an untargeted and excessive manner," says Preisfeld, but only partially agrees with this opinion. The fact is that the animals would eat seeds, carrion and small animals placed flat on the ground, because that's what they eat. "But none of these superstitions, prejudices and fears have been scientifically proven. There is no reliable evidence for any of these fears. The fact that people have such a hatred of these animals is more of a traditional custom."

Magpies and other corvids do steal eggs from other birds, but this amounts to 1% to 10% of their total diet, so it doesn't play a major role. The animals from which they steal the eggs are not endangered animals such as blackbirds or wood pigeons. "In the case of small game, it has been found that shortly after birth, the afterbirth naturally comes out and the young animals detach for the first time. Both are very nutritious for corvids. And as these animals are very clever, they realise this very quickly, fly there and then hate the newborn, which then stands up so that the birds can start excreting. Without any background knowledge, you might think they want to eat the young animal." There were comparative studies in which habitats were selected in which the corvids were protected, i.e. not allowed to be shot, and those where they were allowed to be shot. In comparison with the hunting zones, no excessive increase was observed in the protected zones and the population size remained the same.

Corvids are getting closer to colonisation

"So there are not too many crows and ravens, the population is reasonably stable," says the scientist, explaining why we are noticing them more nowadays. "The natural habitat for the animals is being lost more and more, they are coming closer to our settlements and we are presenting them with everything they need." For example, we like to light up our gardens in the evening and provide the animals with the brightness they love. "We also provide plenty of rubbish for them to eat, for example if the bins are not closed, the compost is not covered or fallen fruit is left on the ground for too long. If you feed, you should only make it accessible to small birds, it is better to take away what falls on the ground, i.e. do not offer ground litter feeding, as this attracts corvids. There are also figures or models you can buy that you can attach to fences or window sills, which also disturb them. Dogs and cats also scare uninvited guests away from the garden."

Sometimes you get the impression of an overpopulation when you see trees with up to 1,000 animals, but they only gather together at night to be stronger, in fact they are individual flocks that usually separate again the following day. "Magpies also give the impression of overpopulation because they build up to 10 mock nests and often only use one."

Corvids regulate our ecosystem

Corvids are an important part of our ecosystem. "They are omnivores," Preisfeld summarises once again, "so they also eat pests such as the wireworm, which we don't like to have in the garden, insects and small animals and thus regulate the whole thing. Predators and prey are in a balanced relationship. This keeps diseases relatively low. They eat everything that is dead, digest it, excrete it again and thus feed it back into the cycle."

Uwe Blass

Professor Dr Gela Preisfeld studied, obtained her doctorate and habilitated at Bielefeld University. After short research stays in Australia and a temporary position at the Goethe University in Frankfurt/Main, she accepted a professorship in Biology and its Didactics, Zoology at the University of Wuppertal in 2006.