Is there a correlation between pollutants and House Sparrow decline?
Looking at recent studies and academic research, I am attempting to find a link in pollution, and the declining House Sparrow (passer domesticus) populations world-wide. A number of hypotheses have been proposed to explain the population decline of the house sparrow in urban areas. These include lack of food, particularly aphids, which adults feed to nestlings, pollution from vehicles running on unleaded fuel, increased predation by domestic cats or sparrow hawks (Accipiter nisus), cleaner streets providing reduced foraging opportunities, loss of nesting sites, particularly under the eaves and in the roofs of houses, pollution (air quality), both in terms of immediate toxicity and indirect toxicity through the food supply, increased use of pesticides in parks and gardens, and disease transmission. I decided to look at a few of these that seemed the most common, to try and help determine an answer to my question.
About House Sparrows
The House Sparrow is a member of the family Passeridae and it is one of the larger sparrows, with a length typically of 160-165mm and a wingspan of 210-255mm (Summers-Smith, 1988). It is a rather large headed, heavy billed, robust passerine. The sexes are dimorphic with the male being boldly patterned. The male is warm brown above, with a grey crown and nape. It has grey cheeks and grey underparts with black round the eyes. The mantle and scapulars are boldly streaked black, chestnut and buff and the tail is dark brown. The bib has black feathers with white tips that are gradually abraded so that by the beginning of the breeding season the bib becomes uniformly black (Summers-Smith, 1988). The female is rather featureless with a grey- brown crown, a pale-buff supercilium, two wing bars and an unmarked throat and breast. The bill becomes darker during the breeding season and a few birds have a completely black bill (Summers-Smith, 1988).
The House Sparrow has a historical commensal relationship with man and has followed his colonization of the majority of the earth. Through the introduction to islands and continents it would otherwise not have reached, it has become one of the most widely distributed land birds in the world (Summers-Smith, 1988). It is only absent from areas such as China, Indochina, Japan and areas of Siberia and Australia to the east and tropical Africa and northern areas of South America to the west (Summers-Smith, 1988). From what I have gathered from talking to a few bird enthusiast friends they have been skeptical to find an issue with possible House Sparrow declines as they find them a more invasive and harmful species to the rest of the avian world. A majority of the people I talked to thought it would be better if the species would just go away. I was a little devastated by this as I don’t think any species should be eliminated. Going through this information I have found that the species is a good...