The discovery of a Burrowing Owl at Sea Island in November prompted the inevitable discussion regarding its origin. BC's wild Burrowing Owl population disappeared by about 1980 (Leupin and Low 2001) and the very small extant population is attributed largely to annual releases of captive-reared owls. I pursued some research about the BC Burrowing Owl Recovery Program, with specific interest in dispersal patterns and return rates in an attempt to, well, justify counting it. Over the course of my research I realized how little I knew about the Recovery Program, so decided to summarize a few items of interest here.
Mitchell et al. (2011) discuss some of the metrics I was looking for while comparing the success of two releases techniques: hard-released birds (i.e., those released directly in to the wild from artificial burrows) versus soft-released birds (i.e., those released in to an enclosure surrounding their artificial burrow prior to the wild). Soft-releases appeared more successful with regard to site fidelity, breeding season survival, fledging rate, and ultimately population recruitment (Mitchell et al. 2011). I suspect soft-release techniques will (have?) gradually phase out hard-releases, and therefore will briefly summarize soft-release results only.
The soft release protocol is to place pairs of captive-reared yearling owls inside artificial burrows where they are held overnight before being released in to an enclosure, which is then removed after approximately two weeks. Released owls display high site fidelity, with 86% of released birds (n=140) from 2005 to 2007 staying following their release. During the same three year period, 69 adult pairs produced 168 fledglings, which had a 69% survival rate during a 40-day post fledging period based on a sample of radio-tracked juveniles. Typically, all owlets are captured inside artificial burrows and banded with a USFWS aluminum leg-band and a coloured alphanumeric leg-band when they are four weeks old. Only 5 of 71 (7%) fledglings from 2005 or 2006 returned in 2006 or 2007, resulting in a population recruitment of 0.17 offspring per soft-released pair. The return rate of released adults during the same period was 2% (1 of 62 adults). However, 28% of 'wild' adults (i.e., adults present prior to the annual release of captive-reared owls) returned again in the subsequent year (Mitchell et al. 2011).
Most adult and young owls leave their release sites by October, but there is little information regarding location of their wintering grounds (Mackintosh et al. 2004). One captive-reared owl wintered in Portland, Oregon in 2001 and again in 2002, and another in Port Townsend, WA in 2002 (Mackintosh et al. 2004). In the winter of 2013, a Burrowing Owl wintered in Tofino and another in Comox, but I do not recall if they were banded and whether their origin was determined.
(Aside: anyone interested in the Burrowing Owl Recovery Program and the associated challenges and successes of reintroduction efforts should check out the Burrowing Owl Conservation Society of BC
web site).
The Sea Island bird was unbanded, which almost certainly eliminates the possibility of a released captive-reared bird because, presumably, none are missed during banding prior to release. Mitchell et al. (2011) mentions all owlets are banded at four weeks old, but it is uncertain whether the occurrence of unbanded birds at release sites indicates presence of wild birds or simply the progeny of released birds missed during previous banding efforts (Leupin 2004). This, coupled with (limited) knowledge of their dispersal patterns, a juvenile bird from a released captive-reared pair may be a possibility.
Unlike many larger owls that moult their primaries and some other flight feathers over two or three cycles, Burrowing Owls have a complete pre-basic moult (Howell 2010), which unfortunately complicates ageing this bird relative to large owls that often have striking moult limits in their primaries. I noticed the primary tips looked quite worn and abraded on our owl, but is it too much wear for juvenal feathers? One wise guy quipped "of course they're worn, they live underground", which may be a valid point, but I haven't got enough experience with Burrowing Owls to confirm or deny.
So, my conclusion: origin uncertain. And that's good enough for me! Every big year needs some controversial tick, and a Burrowing Owl in BC fits that niche quite nicely.
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| #258 - Burrowing Owl - 22 Nov 2015 - Sea Island, Richmond, BC |
References:
Howell, S. N. G. 2010. Molt in North American Birds. Houghton Mifflin Harcourt Publishing Company, New York.
Leupin E. E. 2004. Burrowing Owl
Athene cunicularia in Accounts and Measures for Managing Identified Wildlife - Southern Interior Forest Region V. 2004. BC Ministry of Water, Land and Air Protection. pp. 137-147
Leupin E. E. and D. J. Low. 2001. Burrowing owl reintroduction efforts in the Thomposn-Nicola Region of British Columbia. Journal of Raptor Research 35: 392-398.
Mackintosh, M., E. Leupin and D. Brodie. 2004. Burrowing Owls in B.C. - Science and Stewardship in Action. Proceedings of the Species at Risk 2004 Pathways to Recovery Conference, March 2-6, 2004, Victoria, BC.
Mitchell, A. M., T. I. Wellicome, D. Brodie and K. Cheng. 2011. Captive-reared burrowing owls show higher site-affinity, survival, and reproductive performance when reintroduced using a soft-release. Biological Conservation 144: 1382-1391.
