NATURE NOTES - Written by Dr Martyn Stenning
May 2024 Nature Notes
Today I am considering predator-prey relationships. The biblical statement in 1 Peter 1:24-25 states: “all flesh is as grass”. If we interpret grass as meaning all green, photosynthetic organisms including plants, algae, and some bacteria, then all flesh is indeed made from green things, as all global energy is ultimately solar. Then flesh eating organisms (including insectivorous plants, fungi, and some bacteria) are feeding on animals that consume plants as food in a chain of consumption and so on.
I saw some footage recently of a leopard in India wandering into an abandoned temple and finding a terrified wild pig in one of the rooms, essentially trapped. The leopard looked at the now petrified pig, and then walked on. The leopard was not hungry. Most of us will have seen the wildlife documentaries on TV showing ‘carnivores’ hunting herbivores. These events are quite infrequent, and it takes a lot of patience to film one. However, even cats like to eat grass sometimes, and sheep love to eat snails, to the point where several snail species living on the sheep-grazed grass of the South Downs are described as “sheep snails”. One of them even has a hairy shell and is known as the hairy snail (Trochulus hispidus). Also, deer like to hunt and eat frogs. A single blue tit nestling will have eaten more than 1000 caterpillars and a quantity of spiders before it leaves the nest. It will be just one of about 7 siblings each eating about the same amount, as will the 2 parents (total c. 10,000 prey items).
We may cringe when we see a lion bringing down an elephant or buffalo in Africa, but their physiology commits them to eating meat when they are hungry, and there are probably many days/weeks between such kills. But we are also omnivores, eating both plants and animals, most of the latter are not hunted as such, but raised in a protected and engineered habitat and fed on the best vegetation to maximise their bodily health and killed, ready for us to eat. We also eat the wild animals from the water such as fish and molluscs. All these are hunted by other humans on our behalf. Our effort is usually just to visit a market of some kind and collect them already prepared for cooking where required and consumption. We are still predators, because we depend on another organism to survive, whether it is a plant or an animal or even a fungus like mushrooms, alone or in cheese, yeast in bread, wine and beer and bacteria in yoghurt.
Dr Martyn Stenning
April 2024 Nature Notes
Back in France now to work on our conservation project there. We were delighted to see thousands of Eurasian cranes (Grus grus) flying over our place on migration mainly from Iberia and North Africa. Cranes fly in V-shaped formation in groups of up to c. 500 birds, making memorable and fluty croaking calls, often heard before the birds come into sight.
When setting off, cranes will often find thermals, rising currents of warm air on which they spiral to an altitude of up to ten thousand metres, before flying north to their breeding grounds. Cranes are closely related to coots (Fulica atra) and moorhens (Gallinula chloropus), both common British breeding birds. When you hear these birds call it is understandable that all 3 species are related with similar complex vocal apparatus. However, their external body forms are of course quite different. All three are wetland birds in the taxonomic order of Gruiformes (crane-like birds). The French word for crane is grue, also true for mechanical cranes.
Cranes breed across Northern Eurasia, with small numbers in Norfolk and Somerset. Their main breeding range includes Scandinavia, Siberia, Mongolia and Northern China. Cranes spend winter in the sub-tropics of NW and NE Africa, parts of Iberia, Northern India and SE Asia. The experience of thousands of cranes flying on migration is one of the most moving and spectacular phenomena of the bird world. Many East African wintering cranes migrate via Israel. Autumn migration south is from August to October, and then north to breed from February to early March.
Cranes are omnivorous foragers, eating a wide range of food from roots and seeds to small mammals and birds. They particularly like maize and frogs. Small numbers of cranes over-winter on a maize farm c. 40 km from our place in Aquitaine where they glean un-harvested seeds. Cranes are well known for their courtship dances with much strutting and head bobbing. Cranes pair for life, but if one dies, the other may repair with a new partner. The normal annual clutch is 2 blotchy brown eggs taking about 30 days to incubate before hatching. Crane eggs are often preyed upon by members of the crow family and foxes among others, but adults put up a strong defence. Removed eggs are often replaced within a few weeks. The precocial hatchlings develop rapidly, running around with their parents and swimming within about 24 hours. Breeding begins at the age of 3-6 years and life expectancy is up to 30 to 40 years, but in practice, most wild cranes are thought to live from just 5 – 12 years.
Dr Martyn Stenning