NATURE NOTES - Written by 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


March 2024 Nature Notes

 

One thing we can rely upon in nature is the change of seasons.  Now, as we emerge from winter to spring, the tilt of the planet causes us, in Britain, to be bathed in slightly more solar radiation (sunshine) every day.  Nature is responding to this as I write in February.

 

I have seen my first celandine, wild primrose and daffodil flowers of the year along with many other signals such as gnats dancing and male territorial birds such as blue tits, great tits, robins, starlings, dunnocks, house sparrows, and song thrushes singing seductively to passing females and warning off same sex competitors.  I have also been told of bumblebees flying, which they do as early as possible in the spring to breed.

 

Hazel male catkins are expanding to become huge and blow in the wind like little flags to release their pollen; a bold reminder that spring is developing. Look more closely and you may find the less well known tiny scarlet female flowers on the apex of some of the buds on other parts of the tree.  This is because hazel is a monoecious tree with both male and female flowers on a single plant.  Insects are ambivalent about these flowers as they are largely wind pollinated.  Hence the difference in sex flower size as most pollen will be lost before finding a female flower.  There seems to be strong natural selection for genetic variation in flowering time for this tree, as catkin appearance time is very variable, from early January to March.

 

Breeding is actually on the mind of most animals just now, and the equivalent for plants also.  Frogs are on the move, trying to get back to their natal pond to lay and fertilise huge amounts of spawn.  I suppose the urge to return to the place where they were a tadpole is strong, as the mere fact that they survived suggests it is a good place to breed.

 

Sea trout will be running up the rivers and streams to the head-waters to do the same. The gravel beds they use are called ‘redds’. The male newts also will be developing crests to impress the females to whom they will waggle their tails in the hope of inducing and allowing them to fertilise the female’s eggs that they wrap up in water weed leaves to grow into larval baby newts, also called ‘efts’.

 

The numbers of insects we see will increase hugely as the season develops.  Many of these will be collecting nectar from the emerging flowers, fertilizing the ova with pollen as they do so, and then taking the nectar and some pollen to feed themselves and their youngsters.  Many of these insects then become baby bird food.

 

Dr Martyn Stenning

 

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