Chapter 9: Annual Cycles Flashcards
What are the three main efforts?
- reproduction
- molt
- migration (often)
The annual cycles of birds coincide with _____ _____ and ______.
seasonal resources and opportunities
Birds that are permanent residents undergo three main sequential tasks:
- breeding
- molt
- survival until the next breeding season
Tropical birds base their annual cycles on __ and ___ seasons
wet and dry
Migratory birds face an additional annual challange of
needing to increase body mass for nutrient supply during the migration
All plants and animals exhibit self-sustained oscillations called ______ ______
endogenous rhythms.
Through use of the nervous system and through release of hormones (endocrine system), these biological clocks regulate daily cycles of metabolism, physiology, and behavior. These are called _____ _____
circadian rhythms
Some clocks measure day length and govern events that are tied to an annual cycle (e.g. egg laying, molt, premigratory fattening, migratory restlessness, etc.). These are called______ _____
circannual rhythms.
Circadian rhythms in birds are tied to the activities of two important structures
- the pineal gland
- the suprachiasmatic nucleus of the hypothalamus
The pineal gland is located
on the top of the brain
The pineal gland includes photosensitive cells that direct the rhythmic release _____
melatonin
melatonin regulates …
daily rhythems in accordance with the light-dark cycle
Removal of the pineal gland in House Sparrows causes
normal 24-hour cycles to disappear
One affect of the melatonin is
to regulate the circadian activity of the suprachiasmatic nuclei
All birds have an intrinsic circadian rhythm that is about ___ hours in length
23
increases in daylength cause the growth of testes in
Dark-eyed Juncos.
In the case of reproduction, increasing daylength causes the hypothalamus to release a hormone called
gonadotropin-releasing hormone (GnRH),
GnRH induces the anterior pituitary to release two hormones…
- luteinizing hormone
- follicle-stimulating hormone
What is the effect of luteinizing hormone and follicle-stimulating hormone?
travel to the gonads to cause and increase in growth as well as the production of sperm and eggs
After reproduction has occurred, the gonads will regress. At this point they enter a state called the _____ period, during which the gonads will not regrow, even though photoperiods are still long
photorefractory
Ultimate vs proximate
Ultimate is what has driven the evolution of the breeding season, while proximate factors only effect that one breeding season
Ultimate factors in different species include…
- timing of adequate food sources
- availability of nest sites
- locations of facorable climates
- incidence of predation risk
Proximate factors that induce reproduction include
- temperature
- availability of food
- courtship behaviors
- etc
Reproduction in _____ is closely linked to the availability of pinyon pine seeds.
Pinyon Jays
_____ will breed in the cold of January and February if enough conifer seeds are present.
Red Crossbills
Nesting seasons in temperate latitudes generally last for
3-4 months
Nesting seasons in the tropics last longer, perhaps…
6-10 months
Why do kingfishers and hummingbirds tend to nest during dry seasons when it is common for other birds to nest during the wet season?
Kingfisher: water levels lower
Hummingbirds: when flowers begin to bloom
Caged birds become restless just before the time they would migrate in the wild. This is called
migratory restlessness (Zugenruhe)
What stimulates migratory restlessness, hyperphagia, and fat deposition?
Increaseing day length in the spring
Increaseing day length in the spring stimulates
migratory restlessness, hyperphagia, and fat deposition?
What is hyperphagia?
Overeating
The timing of migration is based roughly on …, but weather factors can alter the timing by fine-tuning it.
internal physiological clocks
The timing for fall migration is actually set by… but the… is the proximate trigger
long photoperiods earlier in the year
shortening of days in the fall
