32 Phenology in Essex: lessons from the past and examples of recent trends
More recent data on the arrival times of eight more familiar bird species have been taken from the
Essex Bird Club reports for the years 1964-1997. These have been examined for changes over time
and compared to Central England Temperatures. It is our intention to examine the arrival and departure
times of spring and autumn migrants in much more detail and publish the findings in the Essex Bird
Report.
Scientific names of species are listed in the appropriate tables.
Results
Table 1 summarises the mean first flowering times for plants in Essex taken from the Royal
Meteorological Society phenological reports. Table 2 summarises similar information regarding
animal phenology. In comparing the data to Central England Temperatures using multiple regression
techniques an influence of temperature on all plant and insect events is apparent. In all cases earlier
appearance was associated with warmer springs. This pattern is far less clear for bird observations.
Overall, the response to temperature is in the 2-9 day range with events such as hawthorn leafing
appearing to be particularly temperature responsive, a feature noted in long-term data from Norfolk
(Sparks, 1999a). Many of the events in Table 1 for 1999 are earlier than, or close to, the earliest date
recorded for 1891-1927. Figure 1 shows the response of wood anemone flowering to February
temperature and Figure 2 shows the response of horse chestnut flowering to April temperature. Both
graphs show how extreme 1999 records were, but these are in keeping with the date-temperature
relationship. Patterns for insects, such as that of the honey bee in Figure 3, are less marked and may
be upset by data points based on single observers. The small number of recorders for birds may
explain why several failed to show a statistically significant relationship with temperature.
Table 1. Mean first flowering dates for plants in Essex 1891-1927. "response" is the number
of days earlier appearance expected from a one degree Celsius warming. Mean dates for
1999 are added for comparison.
______________________________________________Mean Earliest Latest response 1999
Hazel Corylus avellana Feb 3 Jan 10 Mar 3 3.5 Jan 23
Coltsfoot Tussilago farfara Mar 4 Feb 11 Mar 28 2.5 Mar 19
Wood anemone Anemone nemorosa Apr 2 Mar 12 Apr 26 7.0 Mar 8
Blackthorn Prunus spinosa Apr 6 Mar 15 May 7 6.0 Feb 7
Garlic mustard Alliaria petiolata Apr 20 Mar 28 May 12 6.4 Mar 8
Horse chestnut Aesculus hippocastanum May 3 Apr 14 May 17 8.0 Apr 16
Hawthorn Crataegus monogyna May 8 Apr 21 Jun 1 9.4 Apr 21
Ox-eye daisy Leucanthemum vulgare May 27 May 13 Jun 11 6.0 May 21
Dog rose Rosa canina Jun 2 May 15 Jun 18 6.9 May 17
Black knapweed Centaurea nigra Jun 25 Jun 5 Jul 29 4.4
Harebell Campanula rotundifolia Jul 7 Jun 25 Jul 22 9.9
Greater bindweed Calystegia sepium Jul 9 Jun 16 Jul 29 4.7
Ivy Hedera helix Sep 19 Aug 14 Oct 13 8.6
Essex Naturalist (New Series) 17 (2000)