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Nature Notes January 2019


Nature Notes

At a time when some trees and bushes are producing berries I think it is worth thinking about why this happens during Autumn and Winter. We celebrate the holly, ivy and mistletoe at Christmas, but these berries are not appearing now by accident.

Winter is a difficult time for birds, and a time when mortality is high, and the individuals that are best adapted to survival will get through to Spring and attempt to reproduce.

However, the berries are there at this time, not specifically out of altruism to provide food for these birds, rather they are enrolling the birds as seed dispersers and winged conveyers of the plant’s offspring. A bit like the proverbial stork delivering babies.

The three plant species mentioned could not look more different. Holly is our only evergreen broad-leaved tree (if you do not count box which is really a shrub). In fact, all three are evergreen. Also, Holly like the other two is dioecious – has male and female plants and only females have berries of course. Ivy is an evergreen liana climber and mistletoe is a parasitic plant that taps into a host tree’s vascular system. All three produce berries during the autumn and winter.

Many birds overwinter in Britain because of our temperate climate, but also because there is food to be had in the form of a bribe offered by the above plants and others like hawthorn (haws) and rose bushes (hips). The berries are eaten, often whole, and the tasty nutricious coating is digested. However, the seeds pass through the bird’s body and emerge in a tiny packet of compost, often while the bird is roosting in a bush at night, but just as often when flying or looking for more food. The seeds then germinate in the spring and a new generation of the plants is produced in a new location..

This relationship has persisted because all members of the partnership benefit. Moreover, the benefits lead on to successful reproduction meaning that the tradition is perpetuated into future generations.

Dr.Martyn Stenning