Dl. Whitworth et al., Distribution of Xantus' Murrelet Synthliboramphus hypoleucus at sea in theSouthern California Bight, 1995-97, IBIS, 142(2), 2000, pp. 268-279
We radiomarked 153 Xantus' Murrelets Synthliboramphus hypoleucus captured a
l;sea near Santa Barbara Island (SBI), the largest; murrelet colony in the
California Channel Islands, USA. We tracked these radiomarked murrelets in
the Southern California Bight (SCB) aff coastal southern California during
the 1995-97 breeding seasons. In 1995 during mild El Nino conditions, the m
urrelets were distributed in non-upwelling areas. In 1996-97, they were dis
tributed in dense patches, aggregating in cool upwelled waters near the nor
thern Channel Islands or south of San Nicolas Island. Murrelets flew longer
distances from SBI to foraging areas in 1997 ((x) over bar= 111 +/- 44 km)
than in 1996 ((x) over bar= 62 +/- 25 km), but the distances they travelle
d did not differ between months (Apr and May) within years. Mean foraging d
istances fi om SBI were similar for 'incubating' murrelets (determined on t
he basis of repeated visits to SBI) and 'non-incubating' murrelets during t
he colony attendance period. We attributed the law return rate of radiomark
ed murrelets to SBI to the capture and marking of a large proportion of bir
ds that were not actively incubating rather than to any adverse effects of
radio attachment. We believe changes in murrelet foraging patterns between
the 1970s and 1990s are associated with changes in prey resources in the SC
B. Flexibility in the foraging strategies of these murrelets may be related
to the highly variable marine environment at the southern end of the Calif
ornia Current Upwelling System.