Editing Hummingbird (section)

===Adaptation to winter===

Anna's hummingbirds are the northernmost year-round residents of any hummingbird. Anna's hummingbirds were recorded in Alaska as early as 1971, and resident in the [[Pacific Northwest]] since the 1960s, particularly increasing as a year-round population during the early 21st century.<ref name="greig">{{cite journal | last1=Greig | first1=Emma I. | last2=Wood | first2=Eric M. | last3=Bonter | first3=David N. | title=Winter range expansion of a hummingbird is associated with urbanization and supplementary feeding | journal= Proceedings of the Royal Society B: Biological Sciences| volume=284 | issue=1852 | date=5 April 2017 | issn=0962-8452 | pmid=28381617 | pmc=5394677 | doi=10.1098/rspb.2017.0256 | page=20170256}}</ref><ref name="battey">{{cite journal | last=Battey | first=C. J. | title=Ecological release of the Anna's hummingbird during a northern range expansion | journal=The American Naturalist| volume=194 | issue=3 | year=2019 | issn=0003-0147 | pmid=31553208 | doi=10.1086/704249 | pages=306–315| s2cid=164398193 | doi-access=free | bibcode=2019ANat..194..306B }}</ref> Scientists estimate that some Anna's hummingbirds overwinter and presumably breed at northern latitudes where food and shelter are available throughout winter, tolerating moderately cold winter temperatures.<ref name=greig/><ref name=battey/>

During cold temperatures, Anna's hummingbirds gradually gain weight during the day as they convert sugar to fat.<ref name="Beuchat">{{cite journal |author1=Beuchat, C.A. |author2=Chaplin, S.B. |author3=Morton, M.L. |journal=Physiological Zoology|pages=280–295|volume=52|issue=3 |year=1979|title=Ambient temperature and the daily energetics of two species of hummingbirds, ''Calypte anna'' and ''Selasphorus rufus''|doi=10.1086/physzool.52.3.30155751 |s2cid=87185364 }}</ref><ref name= Powers>{{cite journal |last=Powers|first=D. R. |url=http://www.dpowerslab.com/wp-content/uploads/2011/09/PZ1991.pdf |jstor=30158211|title=Diurnal variation in mass, metabolic rate, and respiratory quotient in Anna's and Costa's hummingbirds|journal=Physiological Zoology|volume=64|issue= 3 |year=1991|pages=850–870|doi=10.1086/physzool.64.3.30158211|s2cid=55730100}}</ref> In addition, hummingbirds with inadequate stores of body fat or insufficient plumage are able to survive periods of subfreezing weather by lowering their metabolic rate and entering a state of [[torpor]].<ref name="shankar">{{Cite journal |last1=Shankar |first1=Anusha |last2=Schroeder |first2=Rebecca J. |last3=Wethington |first3=Susan M. |last4=Graham |first4=Catherine H. |last5=Powers |first5=Donald R. |date=May 2020 |title=Hummingbird torpor in context: duration, more than temperature, is the key to nighttime energy savings |url=https://onlinelibrary.wiley.com/doi/10.1111/jav.02305 |journal=Journal of Avian Biology |language=en |volume=51 |issue=5 |pages=jav.02305 |doi=10.1111/jav.02305 |issn=0908-8857 |s2cid=216458501}}</ref>

While their range was originally limited to the [[chaparral]] of California and [[Baja California Peninsula|Baja California]], it expanded northward to [[Oregon]], [[Washington (state)|Washington]], and [[British Columbia]], and east to [[Arizona]] over the 1960s to 1970s.<ref name=battey/> This rapid expansion is attributed to the widespread planting of [[flora|non-native species]], such as [[eucalyptus]], as well as the use of urban [[bird feeders]], in combination with the species' natural tendency for extensive postbreeding [[biological dispersal|dispersal]].<ref name="test">{{cite journal|url=https://birdsoftheworld.org/bow/species/annhum/1.0/introduction|vauthors=Clark CJ, Russell SM|date=2012|title=Anna's hummingbird (''Calypte anna'')|journal=The Birds of North America Online |publisher=The Birds of North America, Cornell University Laboratory of Ornithology|doi=10.2173/bna.226|url-access=subscription}}</ref> In the Pacific Northwest, the fastest growing populations occur in regions with breeding-season cold temperatures similar to those of its native range.<ref name=battey/> Northward expansion of the Anna's hummingbird represents an [[ecological release]] associated with introduced plants, year-round nectar availability from feeders supplied by humans, milder winter temperatures associated with climate change, and acclimation of the species to a winter climate cooler than its native region.<ref name=greig/><ref name=battey/> Although quantitative data are absent, it is likely that a sizable percentage of Anna's hummingbirds in the Pacific Northwest still do migrate south for winter, as of 2017.<ref name=greig/>

Anna's hummingbird is the official city bird of [[Vancouver, British Columbia]], Canada,<ref>{{cite web|url=https://vancouver.ca/parks-recreation-culture/official-city-bird.aspx|title=Official City Bird: Anna's Hummingbird|publisher=City of Vancouver|date=2019|access-date=6 November 2019}}</ref> and is a non-migrating resident of [[Seattle]] where it lives year-round through winter enduring extended periods of subfreezing temperatures, snow, and high winds.<ref name="green">{{cite web |last1=Green|first1=Gregory A. |title=Anna's Hummingbird: Our winter hummingbird |url=https://www.birdwatchingdaily.com/news/species-profiles/annas-hummingbird-our-winter-hummingbird/# |publisher=BirdWatching |access-date=6 November 2019 |date=2 October 2018}}</ref>