Birds

Birds

Water loss
1. REWL (Respiratory evaporative water loss)
  1. Birds lack sweat glands - rely on REWL for thermoregulation
  2. Gullar Fluttering
    1. Rapid movement of flaps in the throat to increase evaporation
2. TEWL (Transepidermal evaporative water loss)
  1. Bird skin permeable, allows moisture through. Not very waterproof
Water Gain
1. Drinking
  1. opportunistic - not always available
  2. Specialist drinking capabilities
    1. Ostrich
2. Metabolic water
  1. 5 - 10 times higher in than in invertebrates and reptiles
3. Diet
  1. Can feed on a high water content species of plants
    1. Ostrich
4. Water re-absoprtion
  1. Nasal salt glands
    1. Produce concentrated salt solutions which is then excreted via the nose - 800 - 900mOsmol
Small Birds = Evaders
1. Sand Grouse
  1. Males carry water to the nest over long distances
    1. Soaks specialised breast feathers
      1. Can carry 40ml of water over long distance
    2. Keeps chicks away from the habitats of predators
2. Larks
  1. Dunn's Lark (ARABIAN DESERT)
    1. Annual rainfall - 90mm
    2. Air temperature in July = 40C
  2. Sky Lark/ Woodland Lark (NETHERLANDS)
    1. Annual rainfall - 750mm
    2. Air temperature in July = 22C
  3. Mesic VS Xeric (balanced vs extreme)
3. Higher Metabolic rate, higher body temperature
Stratergies to reduce water loss
1. Avoid the extremes of hot and arid deserts
  1. Migration
  2. If small, able to evade the heat - Larger birds must endure (ostrich)
2. Nitrogenous waste
  1. Urine
    1. Avian Nephrons
      1. Reptilian type - Lack loops of Henle
      2. Mammalian type = short and sometimes long loops of henle - better at reducing waste
    2. Production of uric acid
      1. Uricoetylic
  2. Renal Function
    1. Reabsorption of water occurs in the colon and cloaca - post renal re-absorption
Large Birds = Endurers
1. Ostrich
  1. Largest living bird - flightless
  2. Reduced levels of urination and urine volume
    1. Urine more concentrated than blood plasma (x2.7 plasma)
  3. Only expires 75% saturated air via REWL
    1. Water saving per day - 200 - 500ml per day
    2. Effective Nasal counter-current flow allows this
  4. Large and enhanced nasal salt glands
2. Lowered metabolic rates, lowered body temperature

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	Created by Adam Heywood almost 6 years ago