The trends in nest success and chick productivity over 25 years
Between 1994 and 2018, over 6000 breeding attempts have been monitored with known outcomes, and these data are summarised in the graph below:
It is immediately obvious that, since 1994, there has been very little change during the period. The fluctuation in nest success (the grey line), which has ranged between 48% and 72%, is probably weather related, and the corresponding trend line shows that there has been a very slight long-term increase.
The fledged brood size of successful nests (orange line) shows a very slight downward trend. This offsets the slight increase in nest success resulting in a near static overall productivity of around 0.9 chicks per breeding attempt (blue line), with the fluctuations also explained by weather.
There has been a claim on a recent television programme that kites are now producing two or three young per pair as a result of supplementary meat provided by feeding stations, and that this explains the unexpected rapid increase in the population growth recorded since the early 1990’s, but the data show that brood size has not increased. Feeding stations could, however, have an effect on adult and 1st winter survival, especially during periods of snow cover when food is difficult to obtain in the wider countryside, and it is changes in survival that are most likely to have led to the population changes witnessed.