Incubation and embryonic development affect the color of eggs of Mountain Bluebirds

Technological and theoretical advances over the past two decades have allowed researchers to quantify eggshell color in ways that were not previously possible. However, differences among studies in the timing of color measurements during laying or incubation and inclusion of data from inviable eggs may affect the results of these studies as well as conclusions based on comparisons among studies. To determine the effect of the timing of color measurements, we compared the color of the eggs of Mountain Bluebirds (Sialia currucoides) during both laying/early incubation and late incubation. We also assessed the influence of egg viability on eggshell color by comparing viable and inviable eggs from the same clutch. We found that all color metrics investigated (blue‐green and UV chroma, brightness, and hue) were significantly different between early and late incubation, and viable and inviable eggs. However, color metrics of eggs measured during early and late incubation and of viable and inviable eggs in the same clutch were correlated. Our results suggest that the timing of color measurements and the viability of eggs have important effects on eggshell color and, therefore, in future studies, investigators should always provide information about the timing of measurements and the viability of eggs measured. Our results also suggest that comparisons among studies where eggshell color was measured at different times and/or the viability of eggs was not determined or reported are possible, given that the color metrics of viable and inviable eggs and of eggs measured at different times in our study were correlated, but those comparisons should be interpreted with caution.     

Blockage errors in studies of the effect of wind on thermoregulatory responses

1. 1.The presence of an animal in a wind tunnel increases the effective wind velocity, and so increases heat transfer rates.

2. 2.Potentially significant errors in thermal conductance and thermoregulatory metabolism measurements may result.

3. 3.In a given wind tunnel metabolism chamber, these errors are size dependent and thus may lead to invalid allometric or adaptive interpretations of data.

4. 4.The errors are also sensitive to the shape, orientation, and characteristics of the fur or feather insulation of the animal. Thus, only approximate guidelines can be given for choosing correction factors.

Influence of larval outbreaks on the climate reconstruction potential of an Arctic shrub

Arctic shrubs have a strong potential for climate and environmental reconstructions in the chronically understudied regions of the high northern latitudes. The climate dynamics of these regions are important to understand because of large-scale feedbacks to the global climate system. However, little is known about other factors influencing shrub ring growth, possibly obscuring their climate signal. For example, as of yet we are not able to differentiate between herbivory or climatically induced growth depressions. Here, we use one of the most common Arctic shrubs, Alnus viridis as a test case to address this question. We sampled Alnus in Kobbefjord, Greenland, measured shrub-ring width and cell wall thickness and built site chronologies of each parameter. We analysed climate-growth relationships, tested their stability over time and employed a pointer-year analysis to detect growth depressions. We employed bootstrapped transfer function stability tests (BTFS) to assess the suitability of our shrub chronologies for climate reconstruction. Correlations with climate data showed strong significantly positive and stable correlations between summer temperature and ring-width with the exception of the recent decade. A climate reconstruction model failed stability tests, when the complete period of record was used for calibration and verification. Wood anatomy analysis uncovered the occurrence of unusual cell structure (very thin cell walls) in the exceptionally narrow ring of 2004, a recorded insect outbreak year in other parts of Greenland. When excluding the affected ring and a recovery period, the reconstruction model passed all tests, suggesting that the unusual 2004 ring was not climate driven, but rather the result of an insect attack. When combining anatomical analysis with traditional ring-width measurements, we move a step further in potentially distinguishing small rings caused by insect attacks from small rings formed in climatically challenging years. While this study does not provide unambiguous evidence, it does provide potential useful methodological combinations to enable more robust climate reconstructions in areas where climatic records are extremely sparse.     

IMU-based ambulatory walking speed estimation in constrained treadmill and overground walking

This study evaluated the performance of a walking speed estimation system based on using an inertial measurement unit (IMU), a combination of accelerometers and gyroscopes. The walking speed estimation algorithm segments the walking sequence into individual stride cycles (two steps) based on the inverted pendulum-like behaviour of the stance leg during walking and it integrates the angular velocity and linear accelerations of the shank to determine the displacement of each stride. The evaluation was performed in both treadmill and overground walking experiments with various constraints on walking speed, step length and step frequency to provide a relatively comprehensive assessment of the system. Promising results were obtained in providing accurate and consistent walking speed/step length estimation in different walking conditions. An overall percentage root mean squared error (%RMSE) of 4.2 and 4.0% was achieved in treadmill and overground walking experiments, respectively. With an increasing interest in understanding human walking biomechanics, the IMU-based ambulatory system could provide a useful walking speed/step length measurement/control tool for constrained walking studies.