Avian - Reproductive System

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Reproductive System

  • 97% of bird species do not have an external penis
    • watefowl have an extruding penis and this is likely an adaptation to ensure the sperm isn't washed away allowing them to fertilise the egg
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Female Reproductive System

  • Only have one ovary
    • only the left ovary and oviduct develops
  • Ovary
  • Infundibulum: fertilisation occurs here
  • When it gets a yolk membrane it gets a shallow iverous layer of albulum and that builds up.
  • Glandular magnum: thick layer of clear liquid is secreted along with various minerals for the development of the egg.
  • Isthumus
  • Uterus: where the majority of the development happens, spends roughly 25 hours here, spends 7 hours getting to the uterus
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Male Reproductive System

  • testes within the body
  • located around the kidneys
  • still have testosterone
    • stimulates the growth and development of the reproductive system
  • 2 testes
  • both testicles are developed and functional
  • ductus deferens is the storage area for sperm
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Potential Problems

  • fertility problems
  • as age increases sperm and egg production decrease as well as mating activity
  • typically, an increase in early embryo death when eggs come from older birds
  • need to find a suitable mate
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Sexual Selection

  • When one parent invests more into the offspring and tend to be choosier about which mate they select
  • the opposite sex will then compete with each other to be chosen
  • intraspecific competition leads to sexual dimorphism
  • fisherian runaway selection resulting in overly exaggerated characteristics
  • most common in Aves
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Avian Mating Systems

  • Polygamy/Polygynandry: each adult may mate with more than one member of the opposite sex
  • Promiscuous: males and females both mate with multiple members of the other sex
  • Monogamy: each adult mates with only one member of the other sex
  • Polygyny: females mate with a large number of males
  • Polyandry: males mate with a large number of females
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Altricial or Precocial

  • Altricial: young which hatch at an early stage of development and require care and feeding from parents.
  • Precocial: young which hatch at an advanced stage and are able to feed themselves almost immediately. 
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