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Wikenigma - an Encyclopedia of Unknowns Wikenigma - an Encyclopedia of the Unknown

Sparrow decline

Large declines of urban and suburban house sparrow (Passer domesticus) populations have been recorded in many towns and cities across Europe. In London, sparrow numbers fell by 60% between 1994 and 2004. The cause(s) of the decline is still not resolved.

Prominent theories include:

• Reduction in the availability of favoured food, either for adults or chicks or both. • Increased levels of pollution. • Loss of suitable nesting sites. • Increased prevalence of disease. • Increased levels of predation.

with other suggestions such as:

• Mobile phone mast radiation. • Fibreglass loft insulation.

To date, no scientific research projects have proven any of the theories - either alone or in combination with others.

Since 2013 there are reports that the rate of decline has stabilised - recent anecdotal evidence suggests that in some areas (of the UK) the numbers may be increasing again.

More details here at the British Trust for Ornithology

Update April 2020. Recent RSPB surveys suggest that sparrow numbers may be on the increase in the UK. See: The Guardian April 2nd, 2020.

Note: In 2000, UK newspaper The Independent offered a prize of £5,000 for a proper scientific explanation of the house sparrow's widespread disappearance - the prize remains unclaimed.


Also see: Cuckoo declineplugin-autotooltip__plain plugin-autotooltip_bigCuckoo decline

"Since the early 1980s Cuckoo numbers [in the UK] have dropped by 65%. The reason for this decline is not known, but it has been suggested that declines in its hosts or climate-induced shifts in the timing of breeding of its hosts could have reduced the…
and Bee Colony Collapse Disorder [ CCD ]plugin-autotooltip__plain plugin-autotooltip_bigBee Colony Collapse Disorder [ CCD ]

"“Colony collapse disorder (CCD) is the phenomenon that occurs when the majority of worker bees in a colony disappear and leave behind a queen, plenty of food and a few nurse bees to care for the remaining immature bees and the que…


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