People tend to think that threatened species are not able to adopt to changes in their environment. Apparently, Great Bustard is an exception to this. Historically, the species has successfully increased its range and was able to colonise even the British Islands. It was able to coexist with low intensity farming for many centuries. However, it has started to decline rapidly during the 20th century.
Although the Great Bustard readily occupies certain agricultural crops, the loss and deterioration of its original habitats due to fragmentation by afforestation, irrigation schemes or infrastructure (e.g. roads, settlements) development present a major threat to the species.
Low breeding success due to agricultural works
Although certain crops, especially alfalfa, attract Great Bustard with more favourable feeding and microclimatic conditions than its natural habitat can provide, the breeding success of the species is lower in this habitats because a large proportion of the nests is lost during agricultural works such as cultivation of the land, mowing of alfalfa or grasslands or harvesting cereals. (Occasionally, chicks and females can be also killed during these works because they usually try to escape threats by squatting flat on the ground). Disturbance during grazing of grasslands, spraying of pesticides, applying fertilisers to arable crops or even recreational activities including birdwatching can also lead to nest failures.
Increased adult mortality due to collision with powerlines
A major cause of adult mortality which seems to affect males more than females. (Collision with fences also appears to be an important mortality factor in some part of the range such as Spain and can increase also elsewhere if grazing regimes change). The impact of the additional adult mortality is especially sever because Great Bustard males reach their maturity at the age of 5-6 years old, while females at 2-4 years old. Hence, population growth rate is more sensitive to changes in adult mortality than changes in fertility.
In addition to agricultural works, artificially high predator pressure (mainly by red foxes) reduces also the survival of eggs and chicks. This is a relatively new phenomena, which relates to recent changes in farming and game management. In Germany, also invasive introduced species also present an increasing threat.