Why Catkins?
It is comforting to be able to see the first flowers of spring. The catkins of the hazel trees are suddenly lengthening, and becoming floppy like lamb’s tails. When the catkins expand it means the male hazel flowers are opening. A close look at the expanded catkin will allow you to see the anthers for yourself.
If you bring them in and keep a twig in water in still air for a day or so, just touching the catkin releases vast amounts of yellow pollen. In the wild the slightest breeze ruffles the wobbly catkin and lifts the pollen. When the pollen grain drops down it lands with luck (considerable luck) on the female. Examine the hazel twig buds that have been kept in the warm and you may be able to find the bright red stigmas of the females peeking out. The stigma (pollen receptive area) is the only part of the flower that ever protrudes from the bud; the rest of the highly reduced flower, and particularly the egg cells, is kept protected from the weather in the centre of the bud.
Once the lucky pollen grain has landed on the stigma, it puts out a fine tube which carries the male nucleus to fertilise the egg and produce the hazel nut we see in autumn.
Flowering early obviously gives the hazel an advantage; leaves do not interfere with the flow of pollen through the air, and this gives a greater chance that the pollen will reach a female somewhere downwind. By shaking in the breeze the catkins’ movement helps launch the pollen grains into the air. When you think of the size of a single grain and the size of the target it has to reach, you might be tempted to think this method of reproduction very inefficient, billions of pollen grains are wasted. Indeed flowers probably evolved and spread through the world because they had a more efficient pollination mechanism than the wind pollinated conifers. The fact that many trees (particularly deciduous) have re-evolved wind pollination suggests that for plants that grow in groups like trees in a wood, the mechanism is better than insect transmission of pollen.
Later in the year you can find the catkins of other trees; hornbeam, birch, poplar, alder, oak, beech, and sweet chestnut. The flowers of ash and elm are not strictly catkin bearing, but they too are wind pollinated. Willow is interesting because it has catkins, but the yellow anthers clearly attract bees too. What part insects play in pollinating willows is something to look into.
Identifying Trees From Their Winter Twigs
The winter gives opportunity to identify trees from their winter twigs. If you use the web and put ‘Tree Identification tips’ into your Google search engine you will find access to the Woodland Trust which provides a ‘nature detectives’ sheet of the common trees as winter twigs which is great to take out with children. Both the Natural History Museum and Woodland Trust websites give extensive methods for adults and children to identify trees.
Spotting Red Kites
One of the birds that we are privileged to be able to observe along the line is the red kite. Having once been almost eliminated from Britain, extensive work and reintroductions have generated a population in the Chilterns that spreads out as far as Harpenden.
It is a relatively large bird of prey and is so distinctive in flight that you can be relatively sure you have identified it. The feature most noticeable is the notched tail, which shows up when you can only see a silhouette of the bird against the sky, but often its reddish tan body can be seen in the sunlight. Look also for the white area near the tips of the wings from the underside. When the wings are spread as the bird soars they appear quite pointed towards the tip so the profile from below is very different from the broad wings with rounded tips shown by the buzzard, the only other bird likely to be soaring. The red kite makes use of soaring as a way of staying airborne using upcurrents from contours or thermals, but it is very agile in flight and can swiftly dip and change direction and sometimes seems to just like darting and weaving for fun.