Geology topics

Research about Bamforth Lake

Source-linked reports with geographic coverage including Bamforth Lake.

5 recordsLinked to original sources

USGS1996

A sexing technique for California Gulls breeding at Bamforth Lake, Wyoming (Una tecnica para determinar sexos en larus californicus reproduciendose en el Lago Bamforth, Wyoming)

We used morphological characteristics to determine the sex of California Gulls ( Larus californicus ) nesting at Bamforth Lake, Wyoming. Using univariate and multivariate techniques, we evaluated sexual dimorphism in five external measurements taken from 614 California Gulls: bill length, bill depth, head-bill length, tarsus length, and body mass. Males were significantly larger than females for all measurements. The greatest difference between the sexes occurred in head-bill length, bill depth, and tarsus length. A multiple logistic regression model was used to assign individuals to a sex class. Sex could be accurately determined using only three variables: head-bill length, bill depth, and tarsus length. Using the logistic function generated from our initial sample, we obtained correct classification of sex in 99.2% and 97.0% of the gulls in two additional validation samples. Utilizamos las características morfológicas para determinar el sexo en una población de Larus californicus anidando en el Lago Bamforth de Wyoming. Evalumos el dimorfismo sexual en la especie utilizando técnicas de univarianza y multivarianza en cinco medidas externas (largo del pico, profundidad del pico, largo de cabeza y pico, largo del tarso y masa corporal) tomadas en 614 aves. Los machos fueron significativamente más grandes que las hembras en todas las medidas. La mayor diferencia entre los sexos se encontró en largo de cabeza y pico, profundidad del pico y largo del tarso. Se usó un modelo de regresión logística multiple para asignar individuos a un grupo genérico. El sexo se podía determinar con precisión utilizando solo tres variables: largo de cabeza y pico, profundidad del pico y largo del tarso. Usando la función logística generada por nuestra muestra inicial, obtuvimos la clasificación al género correcto en 99.2% y 97.0% de las aves en dos muestreos adicionales de validación.

Wyoming↗

USGS1995

Offspring growth in the California gull: Reproductive effort and parental experience hypotheses

Measures of adult feeding and foraging behaviour in the California gull, Larus californicus , were related to the growth of their offspring. Offspring showed significantly higher growth when average feeding interval, a measure of the time interval between feedings, and feeding latency following foraging decreased. The amount of time parents foraged was positively related to offspring growth and negatively correlated with average feeding interval. Either (1) increased foraging efficiency with parental age, or (2) increased reproductive effort with age, could explain age-related differences in patterns of feeding behaviour and their impact on offspring growth. However, data on foraging time support only the hypothesis of increased reproductive effort with parental age.

Wyoming↗

USGS1995

Mark-resighting analysis of a California gull population

California gulls ( Larus californicus ) of known age and sex were censused on their breeding colony in 1979, 1980 and 1984 through 1993. Ages of 235 males and 196 females ranged from 4 to 27 years. Age classes used in the analysis were limited to 17, 4 through 19, and 20 or more as a final age category because data on gulls over 20 were sparse. Survival declined with age in a way that was parsimoniously modelled with a quadratic function. Other factors, sex and time, did not explain any variation in survival. Resighting depended on age, sex and time. Younger adults skipped breeding more frequently than did older adults, and females skipped breeding more frequently than did males. There was also good evidence for time dependence in resighting probability, but its inclusion in the model occurred at the expense of interpretability and precision. In a data set such as this, resighting probability may assume more importance than a mere 'nuisance parameter'. In this study, resighting history measured attendance at the breeding ground. In turn, attendance rates may be a manifestation of reproductive strategy, which can also have consequences for survival. In this situation, there may be heterogeneity in both survival and resighting probability that is unexplained by the model. While such complexity may well be a nuisance to deal with, it can also point to important biological questions.

Wyoming↗

USGS1993

Chick growth in the California Gull: Relationships with hatching asynchrony and parental age

Chick mass and growth during a six-day period were investigated among California Gulls ( Larus californicus ) in 1979 and 1980. In broods of two, levels of hatching asynchrony between siblings ranging from 0 - 4 days were observed. Hatching asynchrony resulted in initial mass differences between siblings that persisted and accelerated with time. Fledging success was unrelated to hatching asynchrony but was related to large offspring mass and increased with parental age. Parental age was unrelated to hatching asynchrony but heavily influenced the brood's gain in mass. Six days after the second egg hatched, chick mass was highest at those levels of hatching asynchrony where mean age of parent was highest. Mass differences between siblings at day six were related to fledging success only to the extent that rapid growth among siblings of older parents usually resulted in large differences in mass. Implications of results to investigations of Lack's brood reduction hypothesis are discussed.

Wyoming↗

USGS1992

Alternate reproductive strategies in the California gull

We analysed 6 years of reproduction data for 176 California gulls ( Larus californicus ) surviving from 1980 to 1988. Using a statistical model adapted from Rao's (1958) and Tucker's (1966) generalized growth curve analysis, we reconstructed the reproductive patterns of gulls aged from 0 to 26 years. Individuals were highly consistent in following one of two patterns of reproduction. In a primary pattern employed by most gulls, individuals skipped breeding less frequently and laid larger clutches as they aged. Clutch size increased to a plateau and remained at high levels throughout remaining life. In an alternate pattern employed by a smaller subset of the sample, clutch size also increased to a plateau. However, as a result of frequent skipping of breeding and smaller clutches, this plateau was considerably lower compared to that of gulls adopting the primary reproductive pattern. Data on fledging success from 1980 and 1984 were consistent with the finding of two reproductive patterns. Gulls adopting the alternate reproductive pattern produce fewer offspring per breeding attempt but survive longer than gulls adopting the primary pattern. The frequency of gulls employing the alternate pattern will increase with age relative to gulls employing the primary pattern. The alternate pattern, and not senescence, may explain why several cross-sectional studies on seabirds report declines among the oldest breeders in measures of clutch size, egg mass, hatching success, and fledging success.

Wyoming↗