Osmoregulation in nestling California gulls at Mono Lake, California

Abstract

1. 1. Hematocrit (Hct), plasma sodium ([Na] pl), chloride ([Cl] pl) and osmotic concentration (Osm pl); volume and concentration of 1.0MNaCl induced salt gland secretion (SGS); and weights of osmoregulatory organs: kidneys, adrenal glands, and salt glands and nonosmoregulatory organs (liver and heart) were determined in nestling California gulls, Larus californiens (CG), on Krakatoa Islet, Mono Lake, California. 2. 2. The mean Hct was 40.0% + 1.0%, the mean [Na] pl and [Cl] pl were 153.9 ± 0.9 and 110.1 ± 0.5 mM ( n = 22); and the mean Osm pl was 323.6 ± 1.3 mOsm/kg ( n = 18). 3. 3. In CG nestlings with a mean age of 10 days ( n = 7), the mean SGS [Na] was 719 ± 19 mM and the birds secreted 81 ± 18% of the injected fluid containing 59 ± 13% of the injected Na. By the mean age of 23 days ( n = 7), mean SGS [Na] was slightly higher (790 ± 30 mM than in younger birds ( P < 0.05), but the percentage of secreted fluid (54 ± 10%) and Na (42 ± 6%) tended to be less. 4. 4. In 18 CG nestlings mean organ weights (% body weight) were: kidneys 1.52 ±0.06%; salt glands, 0.13 ±0.01%, and adrenal glands 0.07 ±0.01%. 5. 5. Nestling CG had significantly greater Hct ( P < 0.001), [Na] pl and [ci] pl ( P < 0.001), Osm pl, ( P < 0.005), and adrenal gland weight ( P < 0.01), compared to nestling glaucous-winged Gulls (GWG), L. glaucescens (Hughes, 1984), which nest under cooler, moister conditions. CG kidney weight was smaller ( P < 0.001); salt gland weight and salt excretion were the same as GWG.