| Home: Special status species: Rhinocerous auklet: Natural history |
SPECIAL STATUS SPECIES: RHINOCEROUS AUKLET (Cerorhinca monocerata)
NATURAL HISTORY |
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| General |
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| Taxonomy: |
Order Charadriiformes;
Family Alcidae. No subspecies are recognized. Despite
its common name, this species is more closely related
to the puffins than the auklets.
|
| Appearance: |
Rhinoceros Auklets
are one of the larger alcids. Adults average 38 cm
(15 in) long and 550 g (19 oz), with males slightly
larger than females. Like all alcids, they have small
wings for their body size so they must flap their
wings continuously and rapidly to maintain flight.
Both sexes have identical plumage; brownish-gray overall,
darker above than below. Adults have two facial plumes
(one behind the eye and one behind the bill) and a
short, upright horn at the base of the bill during
the breeding season. The thick, pointed bill is orange,
fading somewhat after the breeding season. Eye color
varies from brown to yellow. The juvenile appears
similar to the non-breeding adult, lacking both the
feather tufts and beak horn. |
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| Feeding Behavior |
| Overview: |
Generally, Rhinoceros
Auklets feed during the day and at dusk. They may
feed in flocks, but there is no evidence of cooperative
hunting techniques.11
Composition of the diet is variable among colonies
and among years. The diet at Año Nuevo Island
has shifted recently to rockfish-based from anchovy-based
(Figure 5).17
This shift corresponded to a decadal shift in ocean
climate. Annual changes in ocean climate also appear
to impact prey selection. In warm-water years (e.g.,
El Niño conditions) the major prey species
are saury and squid, probably due to decreased abundance
of preferred prey species.17
Northern anchovy, juvenile rockfish, and Pacific saury
are the most common prey items fed to chicks on Año
Nuevo and Southeast Farallon Island.10 |
| Prey Items: |
Rhinoceros Auklets
feed on schooling mid-water fishes, squid, and some
euphuasiids. In central California, common prey species
are Northern anchovy, Pacific saury, juvenile rockfish,
market squid, juvenile salmon, Pacific sardine, Pacific
herring, juvenile sablefish and juvenile lingcod. |
| Method of
Capture: |
These wing-propelled
divers can dive down to 60 m, but most dives are less
than 10 m and average 45 seconds.18 |
Figure 5. Percent number of prey species in Rhinoceros
Auklet chick diet on Año Nuevo Island over
11 years, 1993-2003.17
Download full-size
figures (192 KB PDF). |
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| Reproduction |
|
| Overview: |
Rhinoceros Auklets
breed in colonies on isolated islands. They nest in
either pre-existing crevices or burrows that they
dig with their bills and feet. Breeding activity tends
to be nocturnal or crepuscular, but diurnal activity
occurs at a few colonies. Nocturnal activity appears
to be most common at colonies with a higher incidence
of kleptoparasitism from gulls. Most birds return
to breed at their natal colony. A high percentage
of pairs use the same burrow in consecutive years.19 |
| Time to Maturity: |
3-7 years.17 |
| Longevity: |
17+ 20
|
| Breeding
Season: |
Breeding
activity occurs from mid-April to late-August with
peak egg laying from late-April to mid-May.16 |
| Frequency
of Breeding: |
Annual |
| Clutch Size: |
1 egg |
| Number of Clutches
per Season: |
One 1 clutch; though
a replacement may be laid if the first clutch is lost
early in the season.18
|
| Parental
Care: |
The male and female
take turns incubating the egg (~45 days) and feeding
the young until fledging (~50 days).18 |
| Mating
System: |
Monogamy;
often keeping same mate over successive years18
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