Incubation behaviour of the African jacana

In African jacanas all parental care is by males. The male's daytime attendance of the nest (= incubation constancy) averages 53% and is characterized by frequent, short ‘on’ and ‘off shifts in which he leaves the nest, on average, 35 times per day. Ambient temperatures affect both the incubation constancy and the duration of ‘on’ and ‘off’ shifts: on the coldest (x̄ = 22,9°C) of 4 days of variable weather in which egg and ambient temperatures were monitored together with the male's incubation behaviour, the incubation constancy was 70,9%, the eggs were unattended 28,1%, the ‘on’ shifts were long (x̄ = 22,5 min) and the ‘off’ shifts short (x̄ = 8,4 min). In contrast, on the hottest day (x̄ = 31,3°C) the eggs were unattended 56,5% of the day; they were incubated 6,9% and shaded 36,6%. Both ‘on’ (x̄ = 4,7 min) and ‘off’ (x̄ - 6,3 min) shifts were short. At night, when the eggs were constantly incubated, their temperature remained constant at 34,1 °C (SD = 0,4; n = 69) whereas in daytime their temperature ranged between a daily mean of 33,2–37,1°C (n = 4 days) and between extremes of 27,0–39,6°C. On a hot day (x̄ - 30,0°C) when the male was prevented from shading the test egg its temperature reached a lethal level (43,8°C) in 30 min. It is suggested that the high ambient temperatures prevailing in the African jacana's breeding range have facilitated the evolution of a uniparental care system in this species, but the males’ unusual incubation behaviour associated with high temperatures may also have led to the high clutch predation rate found in this species

Food consumption and pellet production in the black-shouldered kite, Elanus Caeruleus

No Abstract

Measurements and Modeling of Snow Energy Balance and Sublimation from Snow

Snow melt runoff is an important factor in runoff generation for most Utah rivers and a large contributer to Utah\u27s water supply and periodically flooding. The melting of snow is driven by fluxes of energy into the snow during warm periods. These consist of radiant energy from the sun and atmosphere, sensible and latent heat transfers due to turbulent energy exchanges at the snow surface and a relatively small ground flux from below. The turbulent energy exchanges are also responsible for sublimation from the snow surface, particularly in arid environments, and result in a loss of snow water equivalent available for melt. The cooling of the snowpack resulting for sublimation also delays the formation of melt runoff. This paper describes measurements and mathematical modeling done to quantify the sublimation from snow. Measurements were made at the Utah State University drainage and evapotranspiration research farm. I attempted to measure sublimation directly using weighing lysimeters. Energy balance components were measured, by measuring incoming and reflected radiation, wind, temperature and humidity gradients. An energy balance snowmelt model was tested against these measurements. The model uses a lumped representation of the snowpack with two state variables, namely , water equivalent and energy content relative to a reference state of water in the solid phase at 0 degrees Celcius. This energy content is used to determine snowpack average temperature or liquid fraction. The model is driven by inputs of air temperature, precipitation, wind speed, humidity and solar radiation. The model uses physically based calculations of radiative, sensible, latent and advective heat exchanges. An equilibrium parameterization of snow surface temperature accounts for differences between snow surface temperature and average snowpack temperature without having to introduce additional state variables. This is achieved by incorporating the snow surface thermal conductance, which with respect to heat flux is equivalent to stomatal and aerodynamic conductances used to calculate evapotranspiration from vegetation. Melt outflow is a function of the liquid fraction, using Darcy\u27s law. This allows the model to account for continued melt outflow even when the energy balance is negative. The purpose of the measurements presented here was to test the sublimation and turbulent exchange parameterizations in the model. However the weighing lysimeters used to measure sublimation suffered from temperature sensitive oscillations that mask short term sublimation measurements. I have therefore used the measured data to test the models capability to represent the overall seasonal accumulation and ablation of snow

Modeling the effect of vegetation of the accumulation and melting of snow

This work investigates the variability of snow accumulation and differences in the timing of melt and sublimation between open (grass/shrubs) and forest (conifer/deciduous) locations at a mountain study site in the Western US, using a combination of field observations and modeling. Observations include continuous automated climate and snow depth measurements supported by periodic field measurements of snow water equivalent and temperature in four different vegetation classes (grass, shrubs, coniferous forest, deciduous forest) at the TW Daniel Experimental Forest located 30 miles N-E of Logan. The Utah Energy Balance physically based snowmelt model, was enhanced by adding new parameterizations of: i) snow interception and unloading; ii) transmission of radiation through the canopy; and iii) atmospheric transport of heat and water vapor between the snow on the ground, intercepted snow in the canopy and the atmosphere above; to better simulate snow processes in forested areas. The enhanced model was evaluated by comparing model simulations of meteorological conditions (temperature, wind, radiation) and snow properties (water equivalent, depth, temperature) in and beneath the canopy with observations. Observations showed approximately 10 to 20% more snow accumulation in open areas compared to forest areas. Ablation rates were also found to be higher in open areas than in forest areas. In comparison to coniferous forest, deciduous forest had high rates of accumulation and ablation. The model performed well in representing these effects based on inputs such as canopy height, canopy coverage, leaf area index and leaf orientation; thereby improving our ability to simulate and predict snow processes across heterogeneous watersheds. (KEYWORDS: snow accumulation, melt timing, sublimation, interception, snowmelt

Canopy Radiation Transmission for an Energy Balance Snowmelt Model

To better estimate the radiation energy within and beneath the forest canopy for energy balance snowmelt models, a two stream radiation transfer model that explicitly accounts for canopy scattering, absorption and reflection was developed. Upward and downward radiation streams represented by two differential equations using a single path assumption were solved analytically to approximate the radiation transmitted through or reflected by the canopy with multiple scattering. This approximation results in an exponential decrease of radiation intensity with canopy depth, similar to Beer\u27s law for a deep canopy. The solution for a finite canopy is obtained by applying recursive superposition of this two stream single path deep canopy solution. This solution enhances capability for modeling energy balance processes of the snowpack in forested environments, which is important when quantifying the sensitivity of hydrologic response to input changes using physically based modeling. The radiation model was included in a distributed energy balance snowmelt model and results compared with observations made in three different vegetation classes (open, coniferous forest, deciduous forest) at a forest study area in the Rocky Mountains in Utah, USA. The model was able to capture the sensitivity of beneath canopy net radiation and snowmelt to vegetation class consistent with observations and achieve satisfactory predictions of snowmelt from forested areas from parsimonious practically available information. The model is simple enough to be applied in a spatially distributed way, but still relatively rigorously and explicitly represent variability in canopy properties in the simulation of snowmelt over a watershed