Birds

Birds

1. Water loss

   • REWL (Respiratory evaporative water loss)
     • Birds lack sweat glands - rely on REWL for thermoregulation
     • Gullar Fluttering
       • Rapid movement of flaps in the throat to increase evaporation
   • TEWL (Transepidermal evaporative water loss)
     • Bird skin permeable, allows moisture through. Not very waterproof

2. Water Gain

   • Drinking
     • opportunistic - not always available
     • Specialist drinking capabilities
       • Ostrich
   • Metabolic water
     • 5 - 10 times higher in than in invertebrates and reptiles
   • Diet
     • Can feed on a high water content species of plants
       • Ostrich
   • Water re-absoprtion
     • Nasal salt glands
       • Produce concentrated salt solutions which is then excreted via the nose - 800 - 900mOsmol

3. Small Birds = Evaders

   • Sand Grouse
     • Males carry water to the nest over long distances
       • Soaks specialised breast feathers
         • Can carry 40ml of water over long distance
       • Keeps chicks away from the habitats of predators
   • Larks
     • Dunn's Lark (ARABIAN DESERT)
       • Annual rainfall - 90mm
       • Air temperature in July = 40C
     • Sky Lark/ Woodland Lark (NETHERLANDS)
       • Annual rainfall - 750mm
       • Air temperature in July = 22C
     • Mesic VS Xeric (balanced vs extreme)
   • Higher Metabolic rate, higher body temperature

4. Stratergies to reduce water loss

   • Avoid the extremes of hot and arid deserts
     • Migration
     • If small, able to evade the heat - Larger birds must endure (ostrich)
   • Nitrogenous waste
     • Urine
       • Avian Nephrons
         • Reptilian type - Lack loops of Henle
         • Mammalian type = short and sometimes long loops of henle - better at reducing waste
       • Production of uric acid
         • Uricoetylic
     • Renal Function
       • Reabsorption of water occurs in the colon and cloaca - post renal re-absorption

5. Large Birds = Endurers

   • Ostrich
     • Largest living bird - flightless
     • Reduced levels of urination and urine volume
       • Urine more concentrated than blood plasma (x2.7 plasma)
     • Only expires 75% saturated air via REWL
       • Water saving per day - 200 - 500ml per day
       • Effective Nasal counter-current flow allows this
     • Large and enhanced nasal salt glands
   • Lowered metabolic rates, lowered body temperature