That contracts when heated
{{quote-journal|en|date=December 22, 2015|author=|title=Why Do Kestrels Soar?|journal=PLOS ONE|url=http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0145402|doi=10.1371/journal.pone.0145402|volume=|issue=|pages=