Editing Bird feeding (section)

== Impact ==
[[File:"Feed The Birds This Winter...", ca. 1917 - ca. 1919 - NARA - 512477.jpg|thumb|A 1918 call from the [[United States Department of Agriculture|U.S. Department of Agriculture]] to feed birds in the winter.]]
A study conducted in Sheffield, England, found that the abundance of garden birds increased with levels of bird feeding. This effect was only apparent in those species that regularly take supplementary food, raising the possibility that bird feeding was having a direct effect on bird abundance. In contrast, the density of feeding stations had no effect on the number of different bird species present in a neighbourhood.<ref name=sheffield>Fuller, R.A., Warren, P.H., Armsworth, P.R., Barbosa, O. & Gaston, K.J. 2008. Garden bird feeding predicts the structure of urban avian assemblages. Diversity & Distributions 14, 131–137. {{doi|10.1111/j.1472-4642.2007.00439.x}}</ref>

The use of bird feeders has been claimed to cause environmental problems; some of these were highlighted in a front-page article in ''[[The Wall Street Journal]]''.<ref>Sterba, James B. "Crying Fowl: Feeding Wild Birds May Harm Them and Environment", ''Wall Street Journal'', December 27, 2002.</ref>

Prior to the publication of ''The Wall Street Journal'' article, Canadian [[ornithologist]] Jason Rogers also wrote about the environmental problems associated with the use of bird feeders in the journal ''[[Alberta|Alberta Naturalist]]''.<ref>Rogers, J. 2002. Birdfeeding: Another viewpoint. Alberta Naturalist 31: 1-11.</ref> In this article, Rogers explains how the practice of feeding wild birds is inherently fraught with negative impacts and risks such as fostering dependency, altering natural distribution, [[population density|density]] and [[bird migration|migration]] patterns, interfering with ecological processes, causing malnutrition, facilitating the spread of disease and increasing the risk of death from cats, [[pesticides]], hitting windows and other causes.  In the UK, introduced [[eastern gray squirrel]]s can consume significant volumes of food intended for birds.<ref>{{cite journal|last1=Hanmer|first1=Hugh J.|last2=Thomas|first2=Rebecca L.|last3=Fellowes|first3=Mark D. E.|title=Introduced Grey Squirrels subvert supplementary feeding of suburban wild birds|journal=Landscape and Urban Planning|date=2018|volume=177|pages=10–18|doi=10.1016/j.landurbplan.2018.04.004|bibcode=2018LUrbP.177...10H |s2cid=90663919 |url=http://centaur.reading.ac.uk/76790/1/Squirrels_on_feeders_MDEF%20final%20full.pdf}}</ref> An experimental study providing supplementary food during the breeding season found that predation levels by [[Corvidae|corvids]] and eastern gray squirrels were higher when nests were located in close proximity to filled feeders.<ref>{{cite journal |author1=Hanmer, H. J. |author2=Thomas, R. L. |author3=Fellowes, M. D. E.  | year=2017| title=Provision of supplementary food for wild birds may increase the risk of local nest predation| journal=Ibis| volume=159| pages=158–167| doi=10.1111/ibi.12432| issue=1|url=http://centaur.reading.ac.uk/68066/3/Ibis%20paper%20final%20complete.pdf }}</ref>

In a paper in the journal ''[[Oecologia]]'', it was reported that feeding of [[Eurasian blue tit|blue tit]]s and [[great tit]]s with peanut cake over a long time period significantly reduced [[brooding|brood]] size. This was driven by smaller [[Clutch (eggs)|clutch]] sizes in both species and lower hatching success rates for blue tits.<ref>{{cite journal | doi=10.1007/s00442-010-1645-x | pmid=20473622 | volume=164 | issue=2 | title=Does food supplementation really enhance productivity of breeding birds? | year=2010 | journal=Oecologia | pages=311–320 | last1 = Harrison | first1 = Timothy J. E. | last2 = Smith | first2 = Jennifer A. | last3 = Martin | first3 = Graham R. | last4 = Chamberlain | first4 = Dan E. | last5 = Bearhop | first5 = Stuart | last6 = Robb | first6 = Gillian N. | last7 = Reynolds | first7 = S. James| bibcode=2010Oecol.164..311H | s2cid=23419420 }}</ref>
Studies by the [[University of Freiburg]] and [[Environment Canada]] found that [[blackcap]]s migrating to Great Britain from Germany had become adapted to eating food supplied by humans. In contrast blackcaps migrating to Spain had bills adapted to feeding on fruit such as olives.<ref>{{cite web|url=https://www.cbc.ca/news/science/feeding-birds-can-affect-evolution-study-1.799672 |title=Feeding birds can affect evolution: study - Technology & Science - CBC News |publisher=Cbc.ca |date=2009-12-04 |access-date=2011-11-15}}</ref>

Providing supplementary food at feeding stations may also change interactions with other species. [[Aphid]]s<ref>{{Cite journal|last1=Orros|first1=Melanie E.|last2=Fellowes|first2=Mark D.E.|title=Supplementary feeding of wild birds indirectly affects the local abundance of arthropod prey|journal=Basic and Applied Ecology|language=en|volume=13|issue=3|pages=286–293|doi=10.1016/j.baae.2012.03.001|year=2012|bibcode=2012BApEc..13..286O }}</ref> and [[Ground beetle|carabid]] beetles<ref>{{Cite journal|last1=Orros|first1=Melanie E.|last2=Thomas|first2=Rebecca L.|last3=Holloway|first3=Graham J.|last4=Fellowes|first4=Mark D. E.|date=2015-06-01|title=Supplementary feeding of wild birds indirectly affects ground beetle populations in suburban gardens|journal=Urban Ecosystems|language=en|volume=18|issue=2|pages=465–475|doi=10.1007/s11252-014-0404-x|pmid=26190913|issn=1083-8155|pmc=4498636|bibcode=2015UrbEc..18..465O }}</ref> are more likely to be predated by birds near bird feeders.