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Phenology is the study of the timing of natural events, particularly with regard to how they vary from one year to the next. The natural events occur at two main times of the year: spring and fall (autumn).
Historically, people have studied the timing of natural events in the spring far more than those in the autumn. I guess this is because spring is much-anticipated as it brings the promise of warmer and brighter days ahead. Autumn, on the other hand, is much less studied, but this makes it all the more interesting. The factors that affect the timing of autumn events seem more complex than those for spring and consequently there is much to learn. Also, as autumn has been studied much less, there is a greater need or more data, so your observations make an important contribution to our current knowledge of the subject.
What to study?
Which natural events can you look for? This does depend to some extent on what you are interested in because you can study birds, trees, flowers and fungi. Perhaps you would like to have a go at all of them. I'm going to deal with each in turn, giving examples from where I live in the UK. You may have to use different examples, depending on where you live, but this article should give you a good idea of the general principles involved.
Birds
Where you live there will be birds that reside throughout the winter and others that migrate away. You may also have some birds that migrate to your area for the winter. For those exiting migrants you can record the dates when you last see them. Where I live, the most well-known bird for this is the Swallow, but other examples include: Blackcap, Chiffchaff, House Martin, Sand Martin, Spotted Flycatcher, Swift, Turtle Dove, Wheatear, Whitethroat, and Willow Warbler. Note that some of these birds may stay all winter if the weather is mild enough.
How do you record the last date you've seen a bird? Well, it is done the other way round, so to speak. Each day you record the birds you see and after doing this for a few days you will notice that there will be a few days with no records and this indicates that they have departed for sunnier climes. You can then look back at your records to see the last date that you saw them
Some birds will arrive and be resident in the winter. For these birds you can record the first date you see them. Such birds include Bewick's Swan, Fieldfare, Redwing, Waxwing and Whooper Swan.
Trees
Trees are very popular subjects to study in phenology in the autumn as they clearly show the changing season with their yellow leaves and ripening fruits.
With trees there are two things to look out for: leaf tint and leaf drop. Leaf tint means that you can see one leaf that is all yellow, still attached to the tree. (You can see yellow leaves on the ground, but that may have turned yellow after falling). On some trees the leaves turn maroon or red first, rather than yellow.
Now you have to be careful here because some leaves turn brown because the tree is short of water and some turn brown because of an infection from, e.g a fungus, or due to insect infestation. What we are recording is leaves changing colour due to the onset of autumn, not because drought or illness. With autumn tinting the leaves will change colour but still look healthy and keep their shape. A wrinkled, dried brown leaf will have changed due to lack of water and a leaf with brown patches will have an infection. Horse-chestnut is particularly prone to this, so you have to be careful. Also, note that the leaf has to be fully yellow (or red) not pale green or yellow with green on the edges, but completely yellow.
The second thing to record for trees is leaf drop. This is easier to observe, as you record when you see the first leaves on the ground, for whatever reason. Note that in many trees the leaves can fall when they are green, so this can occur before you see any tinting.
For leaf tint and leaf drop you record the date of the first leaves tinting and then a 100% tinted tree, the first leaves to drop and then a 100% bare tree. Note that for some trees, such as Common Lime or Guelder Rose, this can be in July. In Phenology, autumn/fall starts early!
In the past I've recorded intermediate events such as 25% tinting and 50%, but is difficult to judge this sometimes. It is also difficult to compare your assessment of 25% with someone else's, so your results aren't comparable. However, for your own records, It can be a more consistent and reliable feature than first leaf and 100%.
Fruit
One of the notable features of autumn is the production of ripe fruit by a number of different trees and shrubs. Some of the berries and nuts can provide a welcome free source of natural food, but be careful: some are very poisonous as well!
You can record the dates of any tree or shrub that produces nuts or fruit. There are three things that are recorded: the date fruit is ripe, the date fruits drops or falls from a tree and a measure of how good this years crop has been.
How do you know when a fruit is ripe? It is actually a little trickier than you might think. Clearly the fruit changes colour and birds can be seen to eat them, but the fruit may still be a little unripe at this stage. I usually look to see if it has changed colour and it is squashy/compressible as well.
If a fruit has changed colour and dropped from a tree or bush, you can assume it is ripe. Sometimes the fruit drop date is easier to notice than the fruit ripening.
The earliest fruits to ripen where I live are Japanese Cherry and Bird Cherry, both in mid-July. There are many other well-known fruits to keep an eye out for, such as Blackberry(Bramble), Blackthorn(Sloes), Hawthorn, Bittersweet, Yew, Apple and Pear. Just about the last ripening berries you will see are Ivy.
You can also record a measure of how good the year's crop has been for a particular fruit. This is done on a scale of 1-5, 1 being a poor year and 5 a bumper harvest. I find it interesting that some years are good for certain fruits and other years are poor. The judgment of a good/moderate/poor year, though, can only come with experience, so it is not a measurement for beginners to make in their first year.
Wild Flowers
At this time of year, most plants are in flower. One exception is ivy and you can record the first flowering dates for this most important winter food source. Some other late flowerers include Chinese Mugwort, Butterfly Stonecrop and Winter Heliotrope.
Fungi
Autumn is the best season for seeking out fungi and you can keep observing until December. Fungi are a little harder to identify than wild flowers, so it is a good idea to go on a walk with an expert or a local group. Such walks are often called 'fungal forays'. The most common fungi to record are the easiest to recognise, which include Fly Agaric and the Shaggy Ink-cap.
Be Organised
The way you organise your recording in autumn is the same as for the spring: Plan a route around your local neighbourhood, to include all the sights that are best for observing the different events you want to record.
For Autumn observations it is important to have the locations of all your trees carefully noted because once a tree loses its leaves, it can be difficult to identify afterwards. Also, keep a note of bird sightings until you stop seeing them for a few days. You can then look back to see the date they migrated away.
Conclusion
Autumn is a very interesting time of year to record observations, partly because they have been less studied. It also brings to your attention a fascinating series of events with a very different tone and colour to those in spring. It extends your natural history year by a fascinating few months.
As I said earlier, fall/autumn phenology has been studied far less than spring phenology, so if you can submit your observations to a national organisation, they will be very well received and make a real contribution to our current knowledge of the subject.
Michael Knaggs is an enthusiastic and experienced naturalist based in Yorkshire, England. He has been observing birds, flowers and butterflies since he was 12 years old. He is currently a member of the Wild Flower Socity and Bradford Botany Group and contributes to Natures Calendar, an annual phenology survey run by the Woodland Trust.
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