Ingested water equilibrates isotopically with the body water pool of a shorebird with unrivaled water fluxes

We investigated the applicability of H-2 to measure the amount of body water (TBW) and water fluxes in relation to diet type and level of food intake in a mollusk-eating shorebird, the Red Knot (Calidris canutus). Six birds were exposed to eight experimental indoor conditions. Average fractional H-2 turnover rates ranged between 0.182 day(-1) (SD = 0.0219) for fasting birds and 7.759 day(-1) (SD = 0.4535) for birds feeding on cockles (Cerastoderma edule). Average TBW estimates obtained with the plateau method were within the narrow range of 75.9-85.4 g (or between 64.6 and 70.1% of the body mass). Those obtained with the extrapolation method showed strong day-to-day variations (range 55.7-83.7 g, or between 49.7 and 65.5%). Average difference between the two calculation methods ranged between 0.6% and 36.3%, and this difference was strongly negatively correlated with water flux rate. Average water influx rates ranged between 15.5 g/day (fasting) and 624.5 g/day (feeding on cockles). The latter value is at 26.6 times the allometrically predicted value and is the highest reported to date. Differences in H-2 concentrations between the blood and feces (i.e., biological fractionation) were small but significant (-3.4% when fed a pellet diet, and -1.1% for all the other diets), and did not relate to the rate of water flux (chi (2)(1) = 0.058, P &lt;0.81). We conclude that the ingested water equilibrated rapidly with the body water pool even in an avian species that shows record water flux rates when living on ingested marine bivalves.</p

Mapping Agricultural Biodiversity:Legacy data and tensions between ways of seeing fields

Mapping is a core approach used to investigate and display spatial dynamics of biological diversity and habitats. In the Netherlands, agricultural lands occupy nearly two-thirds of the land surface and provide the greatest potential for habitat restoration; particularly in grassland-based dairy production systems, which comprise the largest share of these agricultural lands. When a crop rotation is applied to a long-term grassland, the resulting disruption of ecological complexity requires years–if not decades–to restore, even after reconversion. The availability of high-quality land-use data for measuring the spatio-temporal distribution of grassland legacies is thus essential for monitoring the dynamics of biodiversity in production grasslands. In this study, we reflect on the Basic Crop Registration (BRP) of the Netherlands, an open spatial data infrastructure developed for parcel-level crop registration and examine how it shapes our spatio-temporal understanding of land use. The BRP serves as an administrative basis for numerous national and local-level regulatory and financial arrangements, mainly aimed at agricultural actors. In this study, we repurposed BRP data to introduce a new perspective on depicting the stability of grasslands in a high-intensity agricultural region. We used this data to map the frequency of grassland-to-cropland conversions using 17 years of longitudinal crop records in southwest Friesland, Netherlands. The legacy effects of grassland-to-cropland conversion were investigated in a field study, where significant differences were found between new and long-term grasslands in plant community composition, soil organic matter content, bulk density, soil penetration resistance, and pH. In our analysis of BRP data, we discovered a significant number of grasslands that were recently converted from cropland but that were recorded as long-term grasslands. This affected approximately 12% of the study area from 2005–2021, which prevents the accurate tracking of grassland stability over time. This misclassification also adds uncertainty to the temporal context of the decline in grassland-dependent species in the region. However, using a spatially-explicit mapping approach, these misclassifications can be corrected and help produce an effective measure of grassland stability with potential as an agroecosystem monitoring tool for researchers, land-use planners, and policymakers

Limited Access to Food and Physiological Trade-Offs in a Long-Distance Migrant Shorebird. II. Constitutive Immune Function and the Acute-Phase Response

In response to unbalanced energy budgets, animals must allocate resources among competing physiological systems to maximize fitness. Constraints can be imposed on energy availability or energy expenditure, and adjustments can be made via changes in metabolism or trade-offs with competing demands such as body-mass maintenance and immune function. This study investigates changes in constitutive immune function and the acute-phase response in shorebirds (red knots) faced with limited access time to food. We separated birds into two experimental groups receiving either 6 h or 22 h of food access and measured constitutive immune function. After 3 wk, we induced an acute-phase response, and after 1 wk of recovery, we switched the groups to the opposite food treatment and measured constitutive immune function again. We found little effect of food treatment on constitutive immune function, which suggests that even under resource limitation, a baseline level of immune function is maintained. However, birds enduring limited access to food suppressed aspects of the acute-phase response (decreased feeding and mass loss) to maintain energy intake, and they downregulated thermoregulatory adjustments to food treatment to maintain body temperature during simulated infection. Thus, under resource-limited conditions, birds save energy on the most costly aspects of immune defense.</p