Demography of cape petrels in response to environmental changes

Predicting the responses of populations in changing environments is an important task for ecologists. Understanding the population dynamics of high-latitude breeding species is critical given the particularly rapid environmental changes that occur in these regions. Using long-term mark–resighting data acquired over 53-years in Pointe Géologie, Terre Adélie, Antarctica, we estimated age-specific demographic parameters and evaluated the effect of the environment on survival of a poorly known species, the cape petrel Daption capense. We then modeled the dynamics of this population using a life-history model and performed prospective and retrospective analyses to estimate the sensitivity of the population growth rate to demographic parameters, and to quantify their relative contribution. Survival of cape petrel increased with age, being 0.610 (±0.193) for juveniles, 0.739 (±0.158) for individuals from 2 to 4, and 0.920 (±0.031) for older individuals. Minimum age at first reproduction was 3 years old, the age at which all birds were recruited was 14 years, and mean age at first reproduction was 9.05 (±2.06) years. Adult survival increased over time and was positively correlated with the southern annular mode (SAM). The stochastic population growth rate was estimated at 1.019, and adult survival over age 5 made the largest contribution to variance of the population growth rate. Sensitivity analyses revealed that population regulation was mainly driven by the SAM. Our results suggest that despite the decrease in breeding success, the population of cape petrels at Pointe Géologie increased due to the increase in immature and adult survival.     

Renal response to saline infusion in chicks of Leach's storm petrel (Oceanodroma leucorhoa)

The renal response to infusion of three different saline solutions was studied in chicks of Leach's storm petrel (Oceanodroma leucorhoa). Each of the solutions (125 mmol·1^-1 NaCl at 5.3 ml·h^-1, 250 mmol·l^-1 NaCl at 2.6 ml·h^-1, and 550 mmol·l^-1 NaCl at 1.2 ml·h^-1) provided the same delivery of Nacl but in different volumes of water. Birds infused with 125 mmol·l^-1 NaCl had a glomerular filtration rate of 25.7 ml·h^-1, a urine flow rate of 4.4 ml·h^-1, and excreted 71% of the infused Na⁺ load in the urine. With infusion of 250 mmol·l^-1 NaCl, the glomerular filtration rate was unchanged (23.3 ml·h^-1), but urine flow rate was reduced to 0.93 ml·h^-1 and only 35% of the Na⁺ load was excreted in the urine. Infusion of 550 mmol·l^-1 NaCl induced a sharp decrease in glomerular filtration rate (to 3.8 ml·h^-1) and urine flow rate (to 0.08 ml·h^-1), and only 1.4% of the infused Na⁺ was excreted in the urine. The contribution of different nephron populations to filtration was assessed by the pattern of staining of glomeruli by alcian blue infused during the last 30 min of the saline infusion. The numbers of stained glomeruli did not differ between birds infused with 125 and 250 mmol·l^-1 NaCl (59000 and 55000 glomeruli per kidney, respectively), and the patterns of staining were similar for birds in these two groups. Birds infused with 550 mmol·l^-1 NaCl had lighter staining overall and fewer stained glomeruli (37000 per kidney). This absence of staining was predominant in the smaller size classes of glomeruli, suggesting a selective shutdown of smaller (reptilian-type) nephrons during times of osmotic challenge in these birds. This may be part of an overall suite of water-conserving strategies employed by these chicks during their long confinement with irregular feeding in the nesting burrow.Abbreviations ADH antidiuretic hormone - GFR glomerular filtration rate - MT mammalian-type - P plasma inulin concentration - RT reptilian-type - U urine inulin concentration - V urine flow rate