The Stress of Being a Sparrow

One of the most commonly encountered birds in both town and country is the House Sparrow (Passer domesticus). They are particularly active at this time of year, its mating season (February to May), when individuals and small groups can be seen collecting nesting materials and feeding. Remarkably, P. domesticus has altered its ecology to live in close association with humans. This is thought to have occurred with the development of the first towns and cities, when animals such as horses filled the streets with their seed-rich droppings (1). Such adaptability has given it a vest range, covering most of Africa and Eurasia. Introduction to North America took place in the 1850s on the East Coast of the US: colonisation was so intense that it took only 50 years for P. domesticus to reach the Pacific coast (1). Due to its affinity for human habitation however, it tends to be only locally common in areas (2). The drab looking females contrast with the well marked males, who show contrasting grey, chestnut and black colours.
 

Male House Sparrow, Passer domesticus

As social birds, flocks of P. domesticus are subject to strict hierarchies, and it has been found that these hierarchies are maintained by the physiological state of the bird, namely their size (3). Birds of a large size tend towards dominant positions within the hierarchies, with smaller birds being subordinates. When these positions were altered experimentally, with smaller birds being installed as dominants and vice versa, it was found that both groups suffered increased stress (measured as corticosterone concentrations, energy expenditure and immune functions) as a result of their new positions (4). When the birds were then given a choice of social position they reverted to type, with smaller birds opting for subordinate positions and larger ones for dominance.

References:

1. Beletsky, 2006. Collins Birds of the World pp. 404-406
2. Sterry, 2009. Collins Complete Guide to Irish Wildlife p. 90
3. Goymann and Wingfield, 2004.  Animal Behaviour 67 pp. 591– 602.
4. Lindström et al., 2005. Hormones and Behavior 48 pp. 311 – 320