Do urban birds adapt to a weekly cycle and ‘work’ harder during the weekends?

Weekends are workdays – is the weekly activity cycle of city birds the opposite of people?

Urban environments are increasingly valued for their contribution to conservation, since cities can harbour a rich biodiversity. However, the environmental conditions in those urban ecosystems differ from non-urban habitats and varies a lot, depending on human activity. Cities are warmer, nosier and more polluted than neighbouring “greener” environments. These conditions often have a weekly cycle: noise and pollution (apart from noise and exhaust fumes of lawnmowers) is lower during the weekend than during weekdays.  When doing bird censuses in the city of Paris,  ecology PhD student Assaf Shwartz noticed that there seem to be more birds during weekends than on censuses during workdays.  A statistical test confirmed his hunch: significantly more individuals and more species were registered during weekends than on other days. The same was found for three different, independent inventories of birds: in Paris (2009-10), the wider Paris metropolitan area (2001-3) and urban sites across France (French breeding bird survey, 2001-9). This held only for birds adapted to live in urban habitats , but not in forests, shrub-lands or meadows. Was this due to differences in detectability  (due to reduced noise and disturbance, observers were more effective) or behavioural flexibility, birds adapting to the quieter conditions?  If it were merely the more efficient detection, Assaf argued, public holidays that may fall on any day of the week would similarly show a difference. But it did not:  the richness and abundance of birds on  public holidays  were similar to the richness and abundance on weekdays.  This indicates that several bird species may develop their own weekly activity cycle, to exploit better conditions during quiet weekends.  Birds have very fast metabolism, so they certainly cannot remain inactive during the weekdays –  how general this phenomenon is and why this cycle developed remains to be understood. (Assaf Schwartz, PhD email: shwar.a@mail.huji.ac.il)

Gabor Lövei