Fledging in the common swift, Apus apusweight-watching with a difference

Area of Science:

• Ornithology
• Animal Ecology
• Avian Biology

Background:

• Fledging in common swifts (Apus apus) requires a rapid shift from a sedentary nestling phase to sustained aerial life without post-fledging parental care.
• This transition necessitates physiological and morphological adaptations for immediate independent flight.

Purpose of the Study:

• To investigate the physiological and morphological changes in young common swifts during the pre-fledging period.
• To determine how factors like brood size and resource availability influence these changes and subsequent flight capability.

Main Methods:

• Brood size manipulations and varying resource conditions were used across different breeding seasons.
• Observations focused on chick states, body mass, wing length, and wing loading at fledging.

Main Results:

• Chicks in poorer condition (underfed) exhibited delayed fledging, lower body mass, and shorter wing length.
• Nestlings consistently lost mass in the week before fledging, irrespective of feeding conditions.
• Despite mass loss, nestlings had higher body mass than adults and fledged young, with similar wing loadings at fledging.

Conclusions:

• Young common swifts undergo a 'slimming' process, reducing body mass and potentially water content before fledging.
• This mass reduction, coupled with increased wing length, enhances lift:drag ratio, optimizing flight efficiency for their aerial lifestyle.
• These adaptations prepare fledglings for the demands of continuous flight and survival independent of parental care.