Sparrowhawk population trends and threats
Sparrowhawks are short-lived compared with other birds of prey.
Several factors contributed to a decline in sparrowhawk numbers in the past.
Deforestation over thousands of years, because of man's need for firewood and agriculture, reduced the amount of suitable habitat.
The development of efficient guns and their use in game preservation resulted in indiscriminate killing of birds of prey from the 1840s until they were first given legal protection in 1961.
Sparrowhawks survived this, although their numbers were significantly reduced. Other species fared less well and this illegal killing caused the UK-wide or regional extinction of several other birds of prey species.
Although DDT residues are still found in sparrowhawks, pesticide contamination no longer depresses the population. Illegal killing is also much reduced following the legal protection given to sparrowhawks. Lack of suitable habitat and food availability are probably the main factors limiting sparrowhawk numbers today.
The average lifespan for a sparrowhawk is 2.7 years, and very few live longer than seven years. About one third of the adults die each year, and around two-thirds of the fledged young die in their first year, the most common cause being starvation.
Food availability and the quality of parental care are critical factors influencing a sparrowhawk's survival. Lack of food also limits the production of young. Only just more than half of sparrowhawk nests produce young in any breeding season.
The rate of death among young sparrowhawks peaks in August and September, but adult mortality is at its highest in March and April when food supply is at its lowest.
Prolonged hard winter weather can cause a significant drop in the subsequent breeding population.