Birds: Did Evolution of Biological Novelties Compromise Their Capacity to Effectively Adapt to Extreme Environmental Conditions?

Foremost, the structural, functional and behavioural traits of birds relate directly or indirectly to volancy, i.e., the capacity for powered flight, an elite mode of locomotion that decisively made them what they are today: ‘specialist and extreme animals’. Placing them at the pinnacle of the evolutionary hierarchy, birds possess exceptional biological specialisations which, dispersed across the globe, have provided them with profound survival advantages. The adaptive novelties of birds are above all indicated by the remarkable morphological refinements and physiological specialisations of their respiratory system, the lung-air sac system. To contribute to the ongoing discussions and debates on the impacts of existing and continuing extreme environmental conditions (ECs) on the biology of birds, here, a viewpoint is posed that the adaptive innovations that birds acquired in the past, ostensibly under different ECs, may have undermined their capacity to effectively adjust to different outcomes. To explain this perspective, the following aspects are considered: the specialist and extreme biology of birds; the prevailing brutal ECs that birds must presently endure; and the consequences of having to suffer extreme conditions that include global warming and habitat destruction and pollution. It is proposed that under these existential threats, in general, the adaptive capacities of birds appear to have weakened, rendering them more vulnerable to external pressures. It is suggested that urgent conservation measures, especially for the most threatened species of birds, should be considered.