2 Non-human species as indicators of environmental change

2.1 Birds

As we try to understand the relationship between climate and the distribution and diversity of non-human species, migratory birds are an important source of information for two reasons:

• the timing of arrival and departure in the UK seems to be closely correlated with seasonal changes in temperature

• large networks of well-informed people watch carefully for these arrival and departure events, so we have a lot of data about these events.

Let's look at a couple of examples.

Bird migrants to the UK and Europe are arriving earlier and earlier. If you look at the table on page 4 of the UK Phenology Network's spring 2009 report you can see the pattern for migrants like the house martin and the swift.

The timing of recurring events like migration or raising young is tied to variations in environmental conditions; for example, day length and temperature.

The British Trust for Ornithology (BTO) has extensive records on the timing of egg laying for many UK bird populations. Crick (2007) reports that, between 1971 and 1995, 51 of the 65 species studied showed a pattern of earlier egg laying. Most significantly, this was over a range of species from a number of families over a range of different ecosystems.

Phenology can be used as an indicator of changing environmental conditions. You can find out more information about the BTO programmes and other related organisations that help us get a better picture of how changing climatic conditions affect birds at the websites of the following:

• Euring, the European Union for Bird Ringing

• the BTO's Swallow Roost Project.

In addition to the changes in the timing of recurring natural phenomena, scientists have also begun to notice changes in migration patterns, including changes that relate to the distribution of migratory species and the duration of migrations.

Work by Gregory et al. (2009) indicates that changing climate may mean that the migration routes of spring arrivals like warblers may shift further north. This means a change in the distribution of species like the blackcap and the whitethroat. It also means that these birds will have longer and more difficult migration routes, potentially leading to a reduction in bird numbers.

An overview of this research can be found on the RSPB website.

One of the other things that the modelling by Gregory et al.(2009) tells us is about how changing climate might also effect the range and abundance of species within the UK and Europe, where ‘range’ is a term used to indicate the geographical area in which a species is normally found and ‘abundance’ is an estimate of the number of individuals.

While the Gregory et al. (2009) paper itself is necessarily complex, you can find a useful summary on the European Bird Census Council website. If you look at the graphs you will see that the models indicate that the range (or distribution) and populations of some species will drop, while the range and abundance of other species will increase. You will see that, of those that are predicted to rise, some are species normally found in the south of Europe, while some of those predicted to fall are found in the north of Europe. This is because (as noted in the example of the migratory warblers above) as temperatures rise, the range (or distribution) of species tends to extend northwards. This is good for species in the south of Europe; it is not so good for species in the north. I will look at examples of how this will affect species in the UK later in this unit.

For more background information, see the RSPB's ‘user-friendly’ report entitled ‘Climate change: wildlife and adaptation – 20 tough questions, 20 rough answers’.