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Formerly one of the world's largest colonies, the population of
black-legged kittiwakes (Rissa tridactyla) on Middleton Island has
declined about 80% since 1981. Breeding has been a total or near-total
failure in 14 of the last 16 years (1983-1998). The observed rate of
population decline is equal to the rate of removal of breeding adults
through overwinter mortality (Hatch et al. 1993; Ibis 135:247-254), i.e.,
this colony has experienced little or no recruitment for the better part
of two decades. The situation on Middleton is a particularly severe
example of poor breeding performance in kittiwakes, but many other
colonies in Alaska have exhibited low productivity since at least the mid
1970s. Circumstantial evidence points to an inadequate food supply as the
cause of poor productivity. In contrast to kittiwakes, glaucous-winged
gulls have increased exponentially on Middleton, from fewer than 1,000
birds in the late 1970s to more than 15,000 by the early 1990s. Gulls are
the principal predators on the eggs and young of other species, including
kittiwakes. It is difficult to argue conclusively that food supply is the
ultimate determinant of kittiwake productivity when a population is faced
with intense predation pressure such as currently occurs on Middleton.
Other species also show definite trends on Middleton. Common murres (Uria
aalge) have declined markedly in the last 10 years, whereas rhinoceros
auklets (Cerorhinca monocerata) have increased dramatically since
the late 1970s. To account for contrasting population trends in different
species, it is important that seabird monitoring include measures of three
parameters--populations, productivity, and survival--not just the first,
or first and second of these, as is typically the case (Baille 1990; Ibis
132:151-166). Information on adult survival is needed to assess the
particular life stages affected by untoward changes in the environment
and, most importantly, the time of year and locations at which those
changes occur. The research program on Middleton Island takes advantage of
unique opportunities for close observation and experimental manipulation
of colonial seabirds in artificial nesting habitats. Artificial habitats
promote maximum access and control by investigators while minimizing
disturbance to the birds. The completion of this project over a 5-year
period will result in a one-of-a-kind research facility that would be
difficult to establish anywhere else. Specific objectives of the project
are: (1) Develop research infrastructure on Middleton Island consisting of
artificial and easily accessible breeding habitats for five
colonial-nesting seabird species: black-legged kittiwake, pelagic
cormorant (Phalacrocorax pelagicus), common murre, tufted puffin (Fratercula
cirrhata), and rhinoceros auklet. (2) Establish integrated population
monitoring (numbers, productivity, and survival) for five species (as
above) plus glaucous-winged gulls using natural habitats on Middleton. (3)
Evaluate food supply and predation as limiting factors on kittiwake
reproduction. During FY2000 and FY2001 a subproject funded by the EVOS
Trustee Councile will be completed under this SIS project. The subproject
uses an experimental approach (supplemental feeding) to investigate
whether stress hormones can be used as an indication of food availability
and reproductive performance in kittiwakes. Specific objectives of the
subproject are: (1) Determine whether male and female kittiwakes exhibit
different baseline levels of corticosterone throughout the breeding season
(i.e., prenesting, pre-egg laying, incubation, and brood-rearing) when
they are and are not supplementally fed; (2) Determine whether baselne
levels of corticosterone in unfed individual kittiwakes reflect local
natural food conditions; and (3) Determine whether parents with elevated
levels of corticosterone provide lower levels of parental care (i.e.,
attendance during brood rearing), have delayed breeding chronologies
(i.e., laying, hatching and fledging dates), have lower reproductive
success (i.e., egg laying success, hatching success, fledging success) and
have lower over-winter survival.
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