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<p class=MsoNormal><span style='text-transform:uppercase'>Divoky, G.J. &amp;
Hartert</span>, B.B. 2010. Supernormal delay in hatching, embryo cold tolerance
and egg-fostering in the Black Guillemot <i>Cepphus grylle</i><span
style='font-style:normal'>. </span><i>Marine Ornithology</i><span
style='font-style:normal'> 38: 7-10.</span></p>

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<p class=MsoNormal>We observed an apparent suspension of embryonic growth in
the Black Guillemot <i>Cepphus grylle</i><span style='font-style:normal'>, a
cavity-nesting alcid typically having a two-egg clutch and incubation period of
≈ 28 d.   Limited suspension of embryonic growth is common for species with a
multi-egg clutch, but our observations are apparently the first to document an
extended (≥14 d) suspension prior to the onset of incubation in the wild.  We
found no previous record of the fostering and successful incubation of the egg
of the previous owners by birds usurping a nest cavity. Observations were made
on Cooper Island, in northern Alaska, where manmade structures on a sand and
gravel substrate provide nest cavities.  At the time of clutch completion a
previously non-breeding pair displaced the original nest owners and pushed the
two eggs to the edge of the nest depression.  Approximately 7 d later the
usurping pair moved the displaced eggs back into the nest depression. They
added their own egg to the clutch 14 d later and began incubating all three
eggs.  The initial egg in the original clutch pipped after 28 d of incubation
(45 d after deposition), but died while pipping.  The other hatched after 33 d
of incubation (47 d after deposition); indicating embryonic growth had been
suspended for ≥ 14 days.  During the period of growth suspension, daily
temperatures averaged 2.9°C (range 0.1-7.4°C) with daily minima &lt; 0°C on 12
of the 18 days, demonstrating an extended cold tolerance in the species.  </span></p>

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