Info

trend

Chiffchaff Phylloscopus colybita

21 March

17 March

11 March

P<0.001

Swallow Hirundo rustica

6 April

3 April

31 March

P <0.01

Willow WarblerPhylloscopus trochilus

7 April

2 April

30 March

P<0.001

Blackcap Sylvia atricapilla

15 April

10 April

3 April

P<0.001

Swift Apus apus

1 May

28 April

26 April

P<0.01

Garden Warbler Sylvia borin

4 May

28 April

20 April

P=0.06

Changes through time were examined by regression of annual mean date on year. From Sparks et al. (1999).

Changes through time were examined by regression of annual mean date on year. From Sparks et al. (1999).

Under the presumed influence of long-term climate warming, many birds now arrive in their breeding areas earlier in spring and depart later in autumn than in the past, spending from a few days to a few weeks longer per year in their summer quarters. Such changes have become apparent in a wide range of species at many localities in both Eurasia and North America.1 However, not all species have shown such changes. Some of the exceptions may result from observational deficiencies, for they refer to species that have undergone marked changes in status over the period concerned: a decline in numbers makes it increasingly difficult to detect the earliest arrivals and latest departures, where first and last dates were the measures recorded. Other exceptions are inexplicable, and may be due to changes in conditions that are independent of temperature, such as some types of food supplies.

0 0

Post a comment