Editing Bird migration (section)

==Study techniques==
[[File:Linnuradarid linnutee rändureid seiramas.jpg |thumb |left |Radars for monitoring bird migration. [[Kihnu]], [[Estonia]].]]
Early studies on the timing of migration began in 1749 in Finland, with Johannes Leche of Turku collecting the dates of arrivals of spring migrants.<ref>{{cite journal |last=Greenwood |first=Jeremy J. D. |title=Citizens, science and bird conservation |journal=Journal of Ornithology |year=2007 |volume=148 |issue=Supplement 1 |pages=S77–S124 |doi=10.1007/s10336-007-0239-9 |bibcode=2007JOrn..148...77G |s2cid=21914046}}</ref>

Bird migration routes have been studied by a variety of techniques including the oldest, marking. Swans have been marked with a nick on the beak since about 1560 in England. Scientific [[Bird ringing|ringing]] was pioneered by [[Hans Christian Cornelius Mortensen]] in 1899.<ref>Spencer, R. (1985) ''Marking''. In: Campbell. B. & Lack, E. 1985. ''A dictionary of birds''. British Ornithologists' Union. London, pp. 338–341.</ref> Other techniques include [[radar]]<ref>{{cite web |url=http://virtual.clemson.edu/birdrad/comment.htm |title=Radar Ornithology: Introduction |publisher=Clemson University Radar Ornithology Laboratory |access-date=15 June 2014 |archive-date=11 June 2015 |archive-url=https://web.archive.org/web/20150611063213/http://virtual.clemson.edu/birdrad/comment.htm |url-status=dead }}</ref> and [[GPS satellite|satellite tracking]].<ref>{{cite web |url=http://www.bto.org/science/migration/tracking-studies/cuckoo-tracking |title=Tracking Cuckoos to Africa&nbsp;... and back again |publisher=British Trust for Ornithology |access-date=15 June 2014}}</ref><ref name=":6" /> The rate of bird migration over the Alps (up to a height of 150 m) was found to be highly comparable between fixed-beam radar measurements and visual bird counts, highlighting the potential use of this technique as an objective way of quantifying bird migration.<ref>{{cite journal |last=Schmidt |first=M. |author2=Aschwanden, J. |author3=Liechti, F. |author4=Wichmann, G. |author5=Nemeth, E. |year=2017 |title=Comparison of visual bird migration counts with radar estimates |journal=Ibis |volume=159 |pages=491–497 |doi=10.1111/ibi.12473 |issue=3}}</ref>

Stable isotopes of hydrogen, oxygen, carbon, nitrogen, and sulphur can establish avian migratory connectivity between wintering sites and breeding grounds. Stable isotopic methods to establish migratory linkage rely on spatial isotopic differences in bird diet that are incorporated into inert tissues like feathers, or into growing tissues such as claws and muscle or blood.<ref>{{cite journal |last=Hobson |first=Keith |author2=Wassenaar, Leonard |title=Linking breeding and wintering grounds of neotropical migrant songbirds using stable hydrogen isotopic analysis of feathers |journal=Oecologia |year=1997 |volume=109 |issue=1 |pages=142–148 |doi=10.1007/s004420050068 |pmid=28307604 |bibcode=1997Oecol.109..142H |s2cid=20345396}}</ref><ref>{{cite journal |last=Bowen |first=Gabriel |author2=Wassenaar, Leonard |author3=Hobson, Keith |title=Global application of stable hydrogen and oxygen isotopes to wildlife forensics |journal=Oecologia |year=2005 |volume=143 |pages=337–348 |doi=10.1007/s00442-004-1813-y |pmid=15726429 |issue=3 |bibcode=2005Oecol.143..337B |s2cid=1762342}}</ref>

An approach to identify migration intensity makes use of upward pointing microphones to record the nocturnal contact calls of flocks flying overhead. These are then analyzed in a laboratory to measure time, frequency and species.<ref>{{cite journal |last=Farnsworth |first=A. |author2=Gauthreaux, S. A. |author3=van Blaricom, D. |year=2004 |title=A comparison of nocturnal call counts of migrating birds and reflectivity measurements on Doppler radar |journal=Journal of Avian Biology |volume=35 |pages=365–369 |url=http://virtual.clemson.edu/birdrad/pubs/Farnsworth,Gauthreaux,van%20Blaricom.pdf |doi=10.1111/j.0908-8857.2004.03180.x |issue=4 |access-date=2013-02-02 |archive-date=2017-05-25 |archive-url=https://web.archive.org/web/20170525094637/http://virtual.clemson.edu/birdrad/pubs/Farnsworth,Gauthreaux,van%20Blaricom.pdf |url-status=dead }}</ref>

[[File:EmlenFunnel.svg |thumb |[[Emlen funnel]]]]
An older technique developed by [[George Lowery]] and others to quantify migration involves observing the face of the full moon with a telescope and counting the silhouettes of flocks of birds as they fly at night.<ref>{{cite book |author=Liechti, F. |year=1996 |title=Instructions to count nocturnal bird migration by watching the full moon. |publisher=[[Sempach Bird Observatory|Schweizerische Vogelwarte]], CH-6204 Sempach, Switzerland}}</ref><ref>{{cite journal |last=Lowery |first=G. H. |year=1951 |title=A quantitative study of the nocturnal migration of birds |journal=University of Kansas Publications of the Museum of Natural History |volume=3 |pages=361–472 |url=https://archive.org/stream/universityofkans195103univ#page/n373/mode/1up}}</ref>

Orientation behaviour studies have been traditionally carried out using variants of a setup known as the Emlen funnel, which consists of a circular cage with the top covered by glass or wire-screen so that either the sky is visible or the setup is placed in a planetarium or with other controls on environmental cues. The orientation behaviour of the bird inside the cage is studied quantitatively using the distribution of marks that the bird leaves on the walls of the cage.<ref>{{cite journal |last1=Emlen |first1=S. T. |last2=Emlen |first2=J. T. |year=1966 |title=A technique for recording migratory orientation of captive birds |journal=Auk |volume=83 |issue=3 |pages=361–367 |doi=10.2307/4083048 |jstor=4083048|doi-access=free }}</ref> Other approaches used in pigeon homing studies make use of the direction in which the bird vanishes on the horizon.<ref>Alerstam, 1993. p.352</ref>