Rain more important than windchill for insulation loss in Svalbard reindeer fur

• Main Authors: Christine Cuyler, Nils A. Øritsland
• Format: Article
• Language: English
• Published: Septentrio Academic Publishing 2004-04-01
• Series: Rangifer
• Subjects: conductance; heat loss; heat transfer; Rangifer tarandus platyrhynchus; thermoregulation; wind coefficient
• Online Access: https://septentrio.uit.no/index.php/rangifer/article/view/262

Heat transfer through dry and wet Svalbard reindeer (Rangifer tarandus platyrhynchus) summer and winter midback fur samples was studied in a wind tunnel. A light wetting water spray simulated heavy fog, mist or light rain, while heavy soaking simulated heavy rain. Wind velocities ranged from 0 to 10 m.s-1. Calf fur samples were from June, August and March. Adult fur samples were females from August and March. There was no evidence for increased heat loss from lightly wet fur relative to dry fur. Calm air conductance decreased for calf fur (P’s < 0.05). Adult fur also decreased, however, the difference was not significant (P > 0.05). Further, wind coefficients and regressions for lightly wet fur were similar or below those for dry fur. A thin water film forming on the fur surface may have caused this. It is unlikely that a light rain, fog or mist would cause increased heat loss for Svalbard reindeer, and no increase of metabolic heat production would be needed to maintain thermoregulation. Only the simulated heavy rain dramatically raised heat loss from the fur samples examined regardless of age or season, e.g., heavy soaking increased calm air conductance for all furs (P’s < 0.05). This was likely due to the addition of evaporative heat loss from the fur surface and a reduction in the amount of trapped air within the fur. Windchill was of minor importance, since wind coefficients were generally close to zero, meaning increasing wind velocity only marginally raised heat loss even with the added effect of evaporative heat loss. Rain would cause greater insulation loss than increasing wind velocity in Svalbard reindeer of all ages, with the exception of calves under one month old, which could experience dramatic insulation loss from a combination of heavy rain and windchill. Dry or wet, Svalbard reindeer fur appears to provide better insulation than fur of others of their species. Abstract in Danish / Abstrakt: Varmetab fra tørre og våde Svalbard rensdyr (Rangifer tarandus platyrhynchus) blev studeret fra midtrygs pelsprøver fra henholdsvis sommer og vinter. Pelsprøverne målte 30 cm x 30 cm og blev undersøgt i en vindtunnel. En simuleret tæt tåge eller støvregn blev dannet ved at fugte pelsprøverne med vandsprøjtning, mens gennemblødning simulerede kraftig regnvejr. Vindhastighed varierede fra 0 til 10 m.s-1. Pelsprøver fra kalve blev indsamlet i juni, august og marts, og fra voksne simler i august og marts. Der var ingen tegn på øget varmetab fra let fugtige pelsprøve relativ til de tørre pelsprøve. Vindstillekonduktansen var reducerede i kalvepelsprøve (P’s < 0.05). Samme tendens blev ligeledes observeret i pelsprøverne fra de voksne dyr, men ingen signifikant forskel (P’s > 0.05). Desuden var vindkoefficienter og regressionslinjer fra let fugtige pelsprøve meget lig de tørre pelsprøve, eller mindre. Dette kan være forårsaget af en tynd vandhinde på pelsprøvens overflade. Formodentlig vil der ikke forekomme øget varmetab hos Svalbard rensdyr ved tæt tåge eller støvregn, hvilket betyder at stofskiftet ikke øges for at bibeholde termobalancen. Kun kraftig regn, øgede varmetabet fra samtlige prøver uanset dyrets alder eller årstid. Dette blev påvist ved at vindstillekonduktansen var steget (P’s < 0.05), antageligt forårsaget af det tilføjet fordampningsvarmetab fra pelsens overflade, samt en reduktion af indfanget stilleluft i selve pelsen. Vindchill var af meget lille betydning idet vindkoefficienter generelt var lig nul. Dette medfører at øget vindhastighed kun øger varmetabet meget lidt i våde pelsprøve. Kraftig regnvejr giver større tab af isolation end en øgning i vindhastighed for Svalbard rensdyr, undtagen kalve under en måneden gamle, som bliver udsat for et dramatiske isolationstab som følge af en kombination af kraftig regnvejr og vindfaktor. I både tør eller våd tilstand har Svalbard rensdyr tilsyneladende en bedre isolation end andre underarter af rensdyr.