Estimating Organ Size in Small Migrating Shorebirds with Ultrasonography: An Intercalibration Exercise

Abstract

Organs, even of fully grown adult birds, mammals, and reptiles, may show substantial size changes in relation to specific performances. These changes are difficult to study, because measurements usually can only be obtained following the death of the animal. We explored the use of ultrasonographic imaging, a relatively simple noninvasive technique, to measure size of pectoral muscles and stomach in two small shorebird species (red knots Calidris canutus and golden plovers Pluvialis apricaria). Accuracy of ultrasound measurements in estimating organ mass in red knots was reasonably high. Depending on the equipment used, the error of individual measurements was 20%-25% for the pectoral muscles and 26%-44% for the stomach. In plovers the technique was less accurate, probably because of the low variability of the organs involved. Ultrasound scanning is particularly suited to measure rapidly changing organ sizes over short time intervals. We demonstrate this with an example in which changes in individuals in size of pectoral muscle and stomach were monitored in captive red knots following a change in diet. Ultrasound measures will enable studies on the links between body composition and future behavior and physiology.

Small-scale demographic structure suggests preemptive behavior in a flocking shorebird

“…Gizzard mass is a highly plastic trait (Dekinga et al 2001), but the growth and maintenance of a large gizzard takes time and energy (van Gils et al 2007). Indeed, gizzards of red knots measured in April 2007-2009 using ultrasonography (Dietz et al 1999) were somewhat smaller at A (8.8 g ± 2.9; n = 9) than at B (10.5 g ± 3.4; n = 77), but the differences were not significant (t-test: t = 1.6, df = 10.9, P = 0.14). Besides offering more and possibly higher quality food, A also might be the safer site.…”

Relative roles of temperature and photoperiod as drivers of metabolic flexibility in dark-eyed juncos

“…We added water-soluble recording gel to the skin in the breast region and lowered the scan head into the recording gel for measurement of muscle width. We measured flight muscle width to the nearest 0.01 mm along the short axis of the flight muscles (Dietz et al, 1999;Swanson and Merkord, 2013;. We standardized the position for these measurements by placing a metal ruler across the bottom of the furculum and sliding the scan head forward along the musculature of the right breast so that it just touched the ruler.…”

Ways to be different: foraging adaptations that facilitate higher intake rates in a northerly-wintering shorebird compared to a low-latitude conspecific

“…We measured the response of experimental birds to their diet switch by measuring their gizzards using ultrasound techniques outlined by Dietz et al (1999). We measured the height and width of the gizzards of all birds immediately prior to switching diets and again upon completion of foraging trials.…”

“…Because the size of a shorebird's gizzard is directly related to its ability to crush prey (Piersma et al, 1993;van Gils et al, 2005c), these dual processes can be partially disentangled via the non-invasive measurement of gizzard size (e.g. Dietz et al, 1999). Given their consistently higher winter metabolic demands and near-complete reliance on Macoma as prey in upper Cook Inlet, Alaska, we predicted that ptilocnemis would achieve higher maximum rates of energy intake by processing shell waste more quickly than tschuktschorum.…”