Geology topics

Research about Tutakoke River, Yukon-Kuskokwim Delta

Source-linked reports with geographic coverage including Tutakoke River, Yukon-Kuskokwim Delta.

3 recordsLinked to original sources

USGS2004

Early environment and recruitment of black brant ( Branta bernicla nigricans ) into the breeding population

In geese, growth regulates survival in the first year. We examined whether early growth, which is primarily governed by environmental conditions, also affects the probability that individuals that survive their first year enter the breeding population. We used logistic regression on a sample of Black Brant ( Branta bernicla nigricans ) that were weighed at a known age in their first summer and observed during winter (indicating that they had survived the principal mortality period in their first year) to study whether early growth influenced the probability that those individuals would be recruited into the breeding population. We also examined the effects of cohort (1986-1996), sex, age when measured, and area where individuals were reared. The model with the lowest Akaike's Information Criterion score contained body mass, age (days) at measurement, cohort, sex, and brood-rearing area. Models that included variable mass had 85% of the cumulative model weight of the models we considered, indicating that gosling mass had a substantial effect on probability of them entering the breeding population. Females were more likely to be detected breeding than males, which is consistent with the differential fidelity of the sexes. Of individuals that survived the first year, larger goslings were more likely to become breeders. More recent cohorts were less likely to have been detected as breeders. Our findings indicate that environment during the growth period affects the ability of individuals to enter the breeding population, even after accounting for the effects of growth on survival.

Alaska↗

USGS1991

Growth rate is negatively correlated with hatch date in Black Brant

Arctic geese nest in a highly seasonal environment in which ungrazed plants reach peak nitrogen concentrations when goslings hatch (Sedinger and Raveling 1986). Grazing by geese prolongs peak nutrient concentrations but reduces food availability. This should cause nutrient availability to decline seasonally. Here, we test the hypothesis that late-hatching goslings of Black Brant ( Branta bernicla nigricans ) grow more slowly than those hatching early. We substracted the sizes of wild goslings from those of captive-reared goslings of the same age and regressed the differences against hatch date. Differences between wild- and captive-reared goslings for body mass, tarsus length, and culmen length were significantly negatively related to hatch date; i.e., late-hatching wild goslings were smaller than those hatching early, after accounting for age. We detected no between-year difference in gosling size, but male goslings were larger than females of the same age for all measures. Egg size was only weakly associated with size of goslings 1 mo after hatching, but we detected no effect of other brood characteristics on growth. Seasonal variation in gosling growth rate may favor early nesting in arctic geese.

Alaska↗

USGS1990

Effects of visiting black brant nests on egg and nest survival

I used 2 methods to evaluate the effect of visiting black brant (Branta bernicla nigricans) nests on survival of whole nests and eggs in a single colony on the Yukon-Kuskokwim Delta, Alaska. The first technique regressed survival of nests or eggs during a time interval against interval length. Departure of the y-intercept from 1.0 estimated the short-term effect of the visit at the beginning of the interval. The y-intercepts (±95% CI) for whole nests and eggs during the egg laying period were 1.11 ± 0.31 and 1.06 ± 0.31, respectively. During incubation the same 2 parameters were 0.66 ± 0.31 and 0.66 ± 0.33. The regression method was, thus, imprecise and failed to discriminate among widely varying potential impacts of visitors. The second method involved visiting nests and then immediately revisiting them after pairs had returned to their territories. This method estimated loss of eggs as a result of displacement of territorial pairs during the first visit. Only 1 of 50 eggs was lost (n = 27 nests) as a result of visits during egg laying, whereas no eggs were lost (n = 225 eggs and 55 nests) owing to visits during the incubation period. I conclude that the regression approach is an imprecise tool for estimating visitor impact, but results from both methods indicate little effect of nest visitation under conditions existing on the colony I studied.

Alaska↗