Nutritional Ecology

1
Nutritional Ecology

• Egg Production

2
Physiology Background

• Only left ovary is active (usually)
• Ovary small (pinhead) prior to reproduction
• Rapid Growth (RFG)
• Pituitary release of FSH
• Mostly environmentally induced (photoperiod)
• Hierarchical development (24 hrs)
• Follicles mature, rupture, and enter oviduct as
  ovum

3
Physiology Background

• Oviduct (24-25 hour passage)
• Infindibulum, magnum, isthmus, and uterus
• Ovum fertilized in infindibulum in 30 minutes
• Albumen deposited around yolk in magnum
• Shell deposited in isthmus
• Shell hardened in uterus (about 20.5hrs)

4
RFG
5
RFG

• Rates of RFG vary and may be in response to
• Resource availability
• Predation pressure

6
Egg Production

• Most ducks produced about an egg/day
• Geese and swans have slower rates of egg
  production

7
Where do waterfowl acquire the nutrients for
reproduction?

• Eggs are expensive right?
• Waterfowl eggs relative large with high energy
  content (5-10 of body mass)
• Young are highly precocial

8
Nutritional Ecology

• Ecological and management relevance
• 2 sources
• Exogenous (directly from food)
• Endogenous
• Lipid
• Sources 1g lipid ? 0.78g body fat
• 1g protein ? 0.33g body fat
• 1g carbohydrate ? 0.34g body fat
• Protein (Muscle)
• Need essential amino acids to use protein for
  reproduction
• Mineral
• Stored in bone

9
How did we examine nutritional ecology?

• Females collected randomly on breeding areas
• Proximate Analysis (sequential removal of
  components)
• Carcass homogenized and weighed (w/o feathers and
  reproductive tissues)
• Homogenate dried and weighed
• Lipid extracted from homogenate with petroleum
  ether
• Protein burned from homogenate
• Mineral remains
• Repeat analysis for reproductive tissue and eggs

10
How do you remove confounding with body size?

• Larger birds will have more reserves
• Use PC analysis to control for body size

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Regression

• Is there a relationship between constituents of
  somatic tissue and constituents of reproductive
  tissue
• If somatic tissues are used for reproduction you
  would predict a negative relationship

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Results - Lipid

• Endogenous lipids are generally thought to used
  for reproduction
• Prairie specific?

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Results - Protein

• Proteins for egg production from diet
• Lipid-limited reproduction

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Do these results hold for breeding areas outside
the prairies?

• Northern Pintails at Minto Flats, AK
• Used endogenous lipid and protein for egg
  production
• No comparable data from prairies
• Nest early, limited food
• Northern Shovelers at Minto Flats, AK
• Did not use endogenous reserves
• In contrast to prairie studies
• Later nesting
• Ultimate vs. Proximal Control?

15
Do these results vary temporally?

• Ankney, C. D. and MacInnes, C. D. (1978) Nutrient
  reserves and reproductive performance of female
  lesser snow geese. Auk, 95, 459-471.

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Temporal Variation?

• Gauthier, G., Bety, J., and Hobson, K. A. (2003)
  Are greater snow geese capital breeders? New
  evidence from a stable-isotope model. Ecology,
  84, 3250-3264.
• Late-layers more endogenous

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What next?

• Non-lethal approaches that allow repeat sampling?
• Further understanding of temporal and spatial
  variation?
• Lesser scaup example