চৰাই: বিভিন্ন সংশোধনসমূহৰ মাজৰ পাৰ্থক্য

===প্ৰব্ৰজন===

 

 

Some bird species undertake shorter migrations, travelling only as far as is required to avoid bad weather or obtain food. [[wiktionary:irruptive|Irruptive]] species such as the boreal [[finch]]es are one such group and can commonly be found at a location in one year and absent the next. This type of migration is normally associated with food availability.<ref>{{Cite journal|last=Wilson |first=W. Herbert, Jr. |year=1999 |title=Bird feeding and irruptions of northern finches:are migrations short stopped? |journal=North America Bird Bander |volume=24 |issue=4|pages=113–21 |url=http://elibrary.unm.edu/sora/NABB/v024n04/p0113-p0121.pdf|format=PDF}}</ref> Species may also travel shorter distances over part of their range, with individuals from higher latitudes travelling into the existing range of conspecifics; others undertake partial migrations, where only a fraction of the population, usually females and subdominant males, migrates.<ref>{{Cite journal|last=Nilsson |first=Anna L. K. |year=2006 |title=Do partial and regular migrants differ in their responses to weather? |journal=The Auk |volume=123 |issue=2 |pages=537–47 |url=http://findarticles.com/p/articles/mi_qa3793/is_200604/ai_n16410121|doi=10.1642/0004-8038(2006)123[537:DPARMD]2.0.CO;2 |last2=Alerstam |first2=Thomas |last3=Nilsson |first3=Jan-Åke|issn=0004-8038}}</ref> Partial migration can form a large percentage of the migration behaviour of birds in some regions; in Australia, surveys found that 44% of non-passerine birds and 32% of passerines were partially migratory.<ref>{{Cite journal|last=Chan |first=Ken |year=2001 |title=Partial migration in Australian landbirds: a review |journal=[[Emu (journal)|Emu]] |volume=101 |issue=4 |pages=281–92 |doi=10.1071/MU00034}}</ref> Altitudinal migration is a form of short distance migration in which birds spend the breeding season at higher altitudes elevations and move to lower ones during suboptimal conditions. It is most often triggered by temperature changes and usually occurs when [[territory (animal)|the normal territories]] also become inhospitable due to lack of food.<ref>{{Cite journal|last=Rabenold |first=Kerry N. |year=1985 |title=Variation in Altitudinal Migration, Winter Segregation, and Site Tenacity in two subspecies of Dark-eyed Juncos in the southern Appalachians |journal=The Auk|volume=102 |issue=4 |pages=805–19 |url=http://elibrary.unm.edu/sora/Auk/v102n04/p0805-p0819.pdf|format=PDF}}</ref> Some species may also be nomadic, holding no fixed territory and moving according to weather and food availability. [[True parrots|Parrot]]s as a [[family (biology)|family]] are overwhelmingly neither migratory nor sedentary but considered to either be dispersive, irruptive, nomadic or undertake small and irregular migrations.<ref>{{Cite book|last=Collar |first=Nigel J. |year=1997|chapter=Family Psittacidae (Parrots)|title=[[Handbook of the Birds of the World]], Volume 4: Sandgrouse to Cuckoos |editor=Josep del Hoyo, Andrew Elliott and Jordi Sargatal (eds.) |location=Barcelona |publisher=Lynx Edicions |isbn=84-87334-22-9|pages=}}</ref>