Birds – Part VI VERTEBRATE ZOOLOGY (VZ Lecture28 – Fall 2012 Althoff - reference PJH Chapter 17) Bill Horn ?

Clutch Size How many eggs should a bird produce? Optimal clutch size should = maximum number of young (chicks) the parents can bring to the fledgling size that ___________ their chances of survival Major hypotheses that address this question of clutch size are: a) Trade-off hypothesis b) Predation hypothesis c) Seasonality hypothesis

Trade-off Hypothesis Focuses on behaviors that maximize the _____________ production (i.e., reproductive success) of an individual bird. Another way to say this… …if a bird is long-lived (i.e, >2-3 years), it is better to abandon a nest or produce fewer young per year if there is an obvious risk of being predated (the adult, that is, not the nest) staying put. Many passerines and shorebirds “operate” under this strategy. Many live to be 5-15 years or older Over their lifetime, may produce >10-20 fledglings Easier to feed a ____ young during a nesting cycle

Predation Hypothesis Basically is saying “put all your eggs in _____ basket.” If there is no more likelihood of predation of a nest with eggs, for example, than a nest with 3-4 eggs, then “go for it.” Many upland gamebirds ( wild turkey, quail, prairie chickens, etc.) have this strategy. More frequently, species exhibiting this strategy have ________ young. (snowy owls exception) Risks:a) larger clutch size, more trips to the nests to feed (if not precocial)b) more scent c) more noise (if not precoccial)

Seasonality Hypothesis Variations in clutch size associated with either a) geographic comparisons (north vs. south)b) habitat comparisons (wet vs. dry) Tied closely to amount / available of food…as well as competition there might be for that food from other species nesting at the same time. For example, if rainy season brings on lush vegetation and/or abundance of insects, being able to feed young (or hide young) might be easier…so clutch size could larger. If more competition, then one would expect smaller clutch size

Spectrum of Maturity of hatching Precocial: eyes open, covered with feathers, leave nest after one or two days a) some are independent of parents at hatching (megapods) b) follow parents but find their own food (ducks & shorebirds) c) follow parents and are fed by them (grebes, rails) vs. Altricial: eyes closed, little or no down, unable to leave nest, fed by parents (passerines)

Spectrum of Maturity of hatching Precocial Altricial ______________— eyes open, covered with down, able to walk, remain at nest (gulls & terns) ______________—covered with down, unable to leave nest, fed by parents 1. eyes open: herons and hawks 2. eyes closed: owls

Altricial vs. Precocial Eggs amount of yolk in eggs amount of yolk hatching Chicks size of eyes & brain development of muscles size of gut rate of growth after hatching Greater for

Migration Most pronounced and/or best known for birds Provides a characterization of a vertebrate trait for being able to move long distances (not only birds, but some mammal species, some fishes…and some reptiles) Response to changing (seasonal) a) _______________ b) _______________ Requiresa) endurance b) ability to navigate Some are short-distance migrants, some long- distance.

Fig , p481 PJH Short-tailed shearwater 30,000 km (18,640 miles ) annual migration Note:

Physiological Preparation for Migration Fat becomes principal energy store Birds undergo a period of heavy feeding that results in pre-migratory fattening: a) fat deposits made in body cavity b) fat deposits made in subcutaneous tissue * * this can an increase of up to ______ the ‘regular’ amount present….resulting in increase of 20-50% of the non-fat body mass Known as Zugdispostion (migratory prep) Then Zugstimmung (migratory “mood”) Caged birds, prevented from migrating, exhibit __________________

Orientation and Navigation Two general categories proposed for how birds orient during migration: a) long-distance migration is extension of tendency to explore territory beyond the the home range, learning to recognize ____________ as one goes along b) ability to home through unfamiliar territory using ________ navigation system relying on possibly 1) sun (pigeons experiments) 2) polarized light 3) ultraviolet light 4) magnetism (pigeons) 5) stars …and there may be __________ systems