Energy expenditure and water flux of free‐living Dune Larks in the Namib: a test of the reallocation hypothesis on a desert bird

Abstract

Summary1. Dune Larks ( Mirafra erythroclamys ) are the only avian species that has evolved the capability of surviving in the Namib Sand Sea, one of the driest regions in the world. Their field metabolic rate (FMR) and water flux, as measured by doubly labelled water, during the breeding and non-breeding season are reported here. 2. FMR is relatively constant over the annual cycle, which conforms to the 'reallocation hypothesis'. With data pooled for both seasons, males expended energy at a rate of 97·5 ± 20·4 kJ day -1 ( ± 1 SD) and females at 87·5 ± 13·0 kJ day -1 . The data supported the hypothesis that Dune Larks do not possess a reduced FMR, a result attributable to their elevated basal metabolism. In a previous laboratory investigation, Dune Larks had a low rate of evaporative water loss despite their elevated basal metabolic rate (BMR). The present study demonstrated that this low evaporative water loss translates into a low water influx in the field. 3. The FMR of Dune Lark females equalled 88·1 ± 6·9 kJ day -1 during incubation, and 88·5 ± 9·9 kJ day -1 when they were feeding 8-10-day-old nestlings. These data do not support the idea that the incubation period is a time of low energy demand. 4. Dune Larks had a relatively constant water influx throughout the year. For sexes combined, mass-adjusted values of water influx averaged 0·59 ml H 2 O/(day mass 0·682 ). 5. Calculations showed that neonates received 10 kJ day -1 whereas towards the end of the nestling period, chicks were fed 75 kJ day -1 , the maximum gross energy intake for nestlings. During chick rearing, males increased the amount of food that they found by 57·7%, females by 64·3%, late in the nestling period. 6. Dune Larks foraged in the morning and late afternoon, but were constrained by their environment to seek shade at midday during the breeding season. 7. Metabolic water production plays a significant role in the water economy of Dune Larks. Assuming a mixed diet, 47% of their water intake comes from the oxidation of food stuffs.

Energy and Water Budgets of Larks in a Life History Perspective: Parental Effort Varies With Aridity

“…In addition to our analyses using ANOVA, we performed regression analysis using species averages taking into account phylogeny when appropriate. For these analyses, we added data on FMR and WIR of the Dune Lark (Williams 2001) to our complete data set, including Bar-tailed Desert Lark and Black-crowned Finchlark for which sample sizes were low (Table 1), and correlated these variables with environmental aridity. We used the phylogeny of larks from Tieleman et al (2003a), and placed the Thekla Lark, for which the phylogenetic relationships were not established, as sister species to the Crested Lark.…”

“…1E, Table 1B). In larks, nestling energy expenditure reaches an asymptote at day 6-8 (Williams 2001), and therefore enables calculation of peak energy demand of the brood. In an ANCOVA with log(FMR) as the dependent variable, species as fixed factor, and log(mass) as covariate, the interaction between species and log(mass) was insignificant (F 3,25 ϭ 0.97, P ϭ 0.42).…”

“…To explore if growth rates are correlated with aridity, we added data for Dune Lark nestlings from the Namib Desert (Williams 2001) 4A). A regression model with growth rate constant as dependent variable and aridity and adult body mass as dependent variables, showed a decrease in growth rate with increasing aridity (slope Ϯ 1 SE ϭ 0.115 Ϯ 0.044, t ϭ 2.63, P ϭ 0.04), but no significant effect of adult body mass (slope Ϯ 1 SE ϭ Ϫ0.005 Ϯ 0.003, t ϭ 1.84, P ϭ 0.12).…”

Lipid composition of the stratum corneum and cutaneous water loss in birds along an aridity gradient

“…Q is low in hot, dry deserts and high in cool, wet areas. We collected climatic data from the literature Walter and Lieth, 1967;Williams, 2001), and from www.worldclimate.com and www.onlineweather.com. Because Q increases rapidly when environments become more mesic, we avoided unequal weighting of data for mesic species by using logQ in our analyses .…”

Effects of season, water and predation risk on patch use by birds on the African savannah

“…If possible, birds gather at waterholes to drink (Gill 1990), or while foraging, individuals may select food items with a high water content. Birds, as well as other animals, produce metabolic water as a by-product of the oxidation of various food types, and this will supplement ingested water (Williams 1999(Williams , 2001. Since different food items vary in their water content and in the amount of metabolic water formed during oxidation (Frank 1988), the availability and abundance of specific food items could be an important factor in offsetting the risk of a negative water balance.…”