Annual cycles

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Annual cycles

• Cuculiformes
• Cuckoos, roadrunners, and anis
• 1 family, Cuculidae
• 138 species
• Worldwide

Pied Cuckoo (from India)
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European Cuckoo Obligate brood parasite, must lay
in another species nest All Old World
Cuculiforms are brood parasites
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Intraspecific brood parasitism

• ducks, sparrows, pigeons, grebes, galliforms,
  gulls among others

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Obligate brood parasitism

• Evolved at least 7 times (7 families)
• Cowbirds cuckoos most familiar, but also the
  Black-headed Duck, honeyguides, indigobirds, and
  others
• Pied Cuckoo retains egg in oviduct for 18 hrs
  which aids early hatching

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Gray Cat Bird
Eastern Phoebe
Lay 30-40 eggs per season in weekly sets of 2-5
eggs
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European Cuckoo Video Clip next
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Long-tailed cuckoo Africa
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Pheasant Coucal Australia
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Annual cycles

• Events of the life cycle follow a 12-month cycle
  in most birds centered on breeding

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Annual cycles
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280 arrive on wintering grounds
hyperphagia
100 Recrudescence begins
Hyperphasia
Egg laying begins
Gonadal regression begins
180 Feeding nestlings
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SHADED BAR MIGRANT HATCHED BAR RESIDENT
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Most species breed when food supplies are maximal

• with notable exceptions

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How do birds know when to breed?

• Endogenous rhythm or environmental cue?

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Common Chaffinch circadian rhythm in oxygen
uptake Rhythm drifts 1 hr/day unless synchronized
by Zeitgeber
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European Starling Constant photoperiod
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Red-billed Quelea under constant 12-hr photoperiod
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Garden Warbler
Blackcap
White bars winter molt, Black bars summer
molt
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Conclusion

• Endogenous rhythms exist, but the clock is
  inaccurate

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In cyclic environments, the annual cycle is
entrained by some predictable environmental cue

• For temperate zone birds, the cue is usually
  photoperiod

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Photoperiodism

• Control of reproduction by daylength

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Photoperiodism
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a c
b
a recrudescence b regression b-c
photorefractory phase
IN CAPTIVE BIRDS, PHOTOREFRACTORINESS BEGINS
40-60 DAYS AFTER PHOTOSTIMULATION
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Duration of photorefractory period (months)

• Rook 5
• Starling 4
• Mallard 3

In White-crowned Sparrows exposure to short days
is needed to break the photorefractory phase
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• Mallard Duck, quartz rod conducts light
  directly to hypothalamus
• (B) Testes growth under illumination of equal
  intensity

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Gn-RH
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Photoperiodic response

• Modified by environmental cues

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Great Tit
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Brown Pelicans in Florida nest during winter and
spring, after the hurricane season
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In dry years, leaves of stunted desert annuals
produce phytoestrogens that inhibit reproduction
and prevent the production of young that will
have inadequate food
In wet years, forbs grow vigorously and
phytoestrogens are largely absent