Most birds wintering in New Zealand are of this large dark-backed race L. l. baueri which breeds in Alaska. Studies of radio-tracked birds have found that this population undergoes the longest known non-stop migration of any bird. Apparently they take advantage of major pressure ridges to sling-shot across the Pacific, covering distances of up to 11,000 km (7,200 statute miles) in nine days (Gill et al 2009). They lose up to half their body weight during these marathon non-stop migrations. Sadly, the future of these extraordinary migrants has been imperiled by reclamation projects in the Yellow Sea destroying key migration staging areas for shorebirds in East Asia. This godwit's conservation status was upgraded from "least concern" in 2012 to "near threatened" in 2015 by IUCN as their population continues to plummet. Canon PowerShot SX50 HS.
References:
BirdLife International. 2016. Limosa lapponica. The IUCN Red List of Threatened Species 2016: e.T22693158A93386492. http://dx.doi.org/10.2305/IUCN.UK.2016-3.RLTS.T22693158A93386492.en. Downloaded on 26 March 2017.
Gerard Hutching, 'Wading birds - Bar-tailed godwits', Te Ara - the Encyclopedia of New Zealand, http://www.TeAra.govt.nz/en/wading-birds/page-7 (accessed 26 March 2017)
Gill, R.E.; Tibbitts, T.L.; Douglas, D.C.; Handel, C.M.; Mulcahy, D.M.; Gottschalck, J.C.; Warnock, N.; McCaffery, B.J.; Battley, P.F.; Piersma, T. (2009). "Extreme endurance flights by landbirds crossing the Pacific Ocean: ecological corridor rather than barrier?" Proceedings of the Royal Society B. 276 (1656): 447–457. doi:10.1098/rspb.2008.1142. http://alaska.usgs.gov/science/biology/avian_influenza/pdfs/Gill_et_al_2008_Godwit_Migration.pdf
McCaffery, Brian J. and Robert E. Gill. (2001). Bar-tailed Godwit (Limosa lapponica), The Birds of North America (P. G. Rodewald, Ed.). Ithaca: Cornell Lab of Ornithology; Retrieved from the Birds of North America: https://birdsna.org/Species-Account/bna/species/batgod DOI: 10.2173/bna.581
Piersma, T., Lok, T., Chen, Y., Hassell, C. J., Yang, H.-Y., Boyle, A., Slaymaker, M., Chan, Y.-C., Melville, D. S., Zhang, Z.-W. and Ma, Z. (2016), Simultaneous declines in summer survival of three shorebird species signals a flyway at risk. J Appl Ecol, 53: 479–490. doi:10.1111/1365-2664.12582
Van Gils, J., Wiersma, P., Sharpe, C.J. & Boesman, P. (2017). Bar-tailed Godwit (Limosa lapponica). In: del Hoyo, J., Elliott, A., Sargatal, J., Christie, D.A. & de Juana, E. (eds.). Handbook of the Birds of the World Alive. Lynx Edicions, Barcelona. (retrieved from http://www.hbw.com/node/53890 on 26 March 2017).
Woodley, K. 2013. Bar-tailed godwit in Miskelly, C.M. (ed.) New Zealand Birds Online. www.nzbirdsonline.org.nz