36 Phenology in Essex: lessons from the past and examples of recent trends
Figure 5. The relationship between mean appearance date of cuckoo in Essex 1964-1997
and March mean temperature. For an equivalent number of recorders, the temperature
relationship tends to be less precise in animals than in plants.
Cuckoo
Discussion
Phenological events of plants are less variable in timing than their animal counterparts. This, in
large part, is because of their lower mobility and thus greater probability of encounter by human
recorders. Thus historical plant data for Essex show reliability and a strong response to temperature
despite the small number of recorders involved. In contrast many of the historical animal events
show a weak or no response to temperature. For such variables more recorders or examining events
over a wider geographical area are necessary. This is exemplified when comparing results from the
Essex Bird Reports with those for Essex from the Royal Meteorological Society where the former
demonstrate a much more reliable response. We also need to investigate the response of species to
temperatures along migration routes. Individual records, unless they are of considerable duration,
are of little value on their own. However, gathered together they can be a powerful source of
information.
There is now considerable evidence of change in our natural world. The availability of phenological
data such as those shown here allows us to quantify the rate of change. Menzel & Fabian (1999)
have shown wide-scale changes in the growing season of trees across Europe. Closer to home we
have detected changes in the migration timing of birds (Mason, 1995; Sparks, 1999b) and this may
also be apparent across Europe (Sparks et al, 1999). Invertebrate phenology shows a similar response:
the timing of first and peak appearance of most UK butterflies has advanced over the last two
decades (Roy & Sparks, in press). Many phenological events arc very sensitive and several have
recently been adopted as candidate indicators of climate change (Cannell, Palutikof & Sparks, 1999).
Even on the small scale reported here, changes are evident, and Essex recorders have contributed,
Essex Naturalist (New Series) 17 (2000)