“…The most widely used sedimentary proxies for birds are geochemical, and can be classified as either trace element (Liu et al 2006a, 2006b, Xie and Sun 2008, Brimble et al 2009, Huang et al 2009, Nie et al 2014a or stable isotope (Hawke 2004, Sun et al 2005, Yuan et al 2010, Keatley et al 2011, Liu et al 2013, Nie et al 2014b) proxies. A key strength of geochemical proxies is their ability to record marine inputs into terrestrial ecosystems, and therefore their main utility has been for inferring the past distribution (e.g., Hawke et al 1999, Yuan et al 2010), colony longevity (Hawke 2004), and population trends (e.g., Sun et al 2005, Liu et al 2006a, Huang et al 2009 of marine birds such as procellariiforms and penguins.…”