Little is known about the breeding ecology of Kittlitz's Murrelets (Brachyramphus brevirostris), a species suspected to have experienced both local and regional population declines in recent years. We studied aspects of their breeding ecology on Kodiak Island, Alaska, to better understand this poorly described member of the family Alcidae. We found 53 nests of Kittlitz's Murrelets during our study (2008–2011) and placed nest cameras at 33 nests to collect data on parental nest attendance, nestling provisioning, and nest survival. Incubation shift exchanges by adults generally occurs either prior to sunrise or after sunset. Adults brooded nestlings for just one day after hatching and did not attend nests thereafter except during provisioning visits. Adults provisioned nestlings an average of 107 times during nestling periods, with a single fish delivered during each visit. Pacific sand lance (Ammodytes hexapterus), a high‐lipid forage fish, accounted for 92% of fish delivered to nestlings. Nestlings grew rapidly, with a logistic growth rate constant (K) of 0.291, the highest rate yet documented among semiprecocial alcids. Young fledged an average of 25 d after hatching, when their body mass had reached an asymptote of 135.5 g, or 57% of adult body mass. Age at fledging and asymptotic nestling body mass (percent of adult mass) were low compared to other semiprecocial alcids. The mean number of young fledged per nest was 0.093, with 47% of nests predated, and nestlings dying prior to fledging at 21% of nests. The low number of parental provisioning visits, rapid nestling growth rates, and short nestling periods are consistent with adaptations to reduce the likelihood of nest predation and the energy expended by parents. The risk of nest predation and high energetic cost of breeding may make the reproductive success of Kittlitz's Murrelets more sensitive to declines in the availability and quality of their prey than most other alcids.
The Kittlitz's murrelet Brachyramphus brevirostris is a small, noncolonial seabird endemic to marine waters of Alaska and eastern Russia that may have experienced significant population decline in recent decades, in part because of low reproductive success and terrestrial threats. Although recent studies have shed new light on Kittlitz's murrelet nesting habitat in a few discrete areas, the location and extent of suitable nesting habitat throughout most of its range remains unclear. Here, we have compiled all existing nest records and locations to identify landscape-scale parameters (distance to coast, elevation, slope, and land cover) that provide potential nesting habitat in four regions: northern Alaska, Aleutian Islands, Alaska Peninsula Mountains and Kodiak Island, and Pacific Coastal Mountains (including nearshore interior Canada). We produced a final map classifying 12% (70,411 km2) of the lands assessed as potential Kittlitz's murrelet nesting habitat, with dense but distinct patches in northern Alaska and a more uninterrupted, narrow band extending across the Pacific Coastal Mountains, Alaska Peninsula Mountains, and Aleutian Islands. The extent of habitat-capable parameter values varied regionally, indicating that the Kittlitz's murrelet may be able to use a variety of habitats for nesting, depending on availability. Future nesting habitat studies could employ spatially random sampling designs to allow for quantitatively robust modeling of nesting habitat and predictive extrapolation to areas where nests have not been located but likely exist.
Most seabird species nest colonially on cliffs or islands with limited terrestrial predation, so that oceanic effects on the quality or quantity of prey fed to chicks more often determine nest success. However, when predator access increases, impacts can be dramatic, especially when exposure to predators is extended due to slow growth from inadequate food. Kittlitz's Murrelet (Brachyramphus brevirostris), a rare seabird having experienced serious declines, nests solitarily on the ground in barren, often alpine areas where exposure to predators is generally low. Nestling growth rates are exceptionally high and nestling periods very short relative to other Alcidae. This strategy reduces duration of exposure to predators, but demands adequate deliveries of high-energy prey. In an area where foxes can access nests, we investigated whether varying energy content of prey fed to chicks could alter growth rates and resulting duration of predator exposure, and whether prolonged exposure appreciably reduced nest success. From 2009 to 2016, we monitored 139 nests; 49% were depredated (almost all by foxes) and 25% fledged. Prey fed to nestlings were 80% Pacific sand lance (Ammodytes personatus) and 19% capelin (Mallotus villosus), with capelin having 2.3× higher energy content per fish. In a year of slow chick growth, increased sand lance energy density of 31% (4.29-5.64 kJ/g, within published values), or increased proportion of capelin in the diet from 5.6% to 27.2%, would have allowed maximum chick growth. Maximum growth rates were attainable by delivering only 1.9 capelin/d versus 5.5 sand lance/d. Slow growth increased time to fledging by up to 5 d, decreasing survival by 7.7% (0.142-0.131). Breeding propensity of Kittlitz's Murrelet averages only 20%, so even small changes in nest success could affect populations. Although nest success was limited mainly by predation, oceanic effects on prey quantity and quality had overriding impacts in one year (2015 heat wave), and small but substantive effects in other years by mediating exposure to predation. Climate warming that decreases availability of high-energy forage fish, or increases expansion of predators into nesting habitats, may disproportionately affect this sensitive species and others with predator-accessible nests and demands for energy-rich prey.
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