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What is phenology?

Phenology is the study of seasonal changes in plants and animals from year to year - such as flowering, emergence of insects and migration of birds - especially their timing and relationship with weather and climate.

Nature’s Calendar recorders make notes of certain events which happen to certain species during changing seasons. Examples of events we record throughout the year include:

Photograph of native bluebell Hyacinthoides non-scripta.

Trees and shrubs

Budburst, first leaf, first flower, fruit ripe, first tint, full tint, leaf fall, bare tree.


First flower.

Migratory birds

First and last recorded.

Resident birds

First heard singing, first nestbuilding, first feeding young and young first seen.


First recorded.

Changing phenology

Rising temperatures mean that phenology is changing.

Scientific studies using Nature’s Calendar data have indicated how phenology is changing and some are beginning to suggest what the impact of this will be:

• Spring events like budburst, leafing and flowering are getting earlier.
• Fruiting of trees and shrubs is getting earlier.
• Late autumn events such as leaf fall may be delayed.

The overall the period of active plant growth each year is lengthening. A recent study by the Met Office estimated it to be, on average, a month longer during the past decade compared to the period between 1961 and 1990.

It has been calculated that, across Europe as a whole, spring is now advancing by 2.5 days per decade.

These changes may affect food chains for plants, insects and birds, with some species potentially falling out of sync with each other because each responds individually and at different rates to rising temperatures.

Changing phenology is one of the first observed responses to climate change. Eventually, species may also change their abundance, range (i.e. where they are found geographically) and even become locally extinct in areas that are less favourable. So the science of phenology provides a powerful ‘early warning’ of species that could be ‘winners’ and ‘losers’ as the climate changes. 

Visit our Nature's Calendar website