Lecture 9 - Avian Life Histories Chapters 12 16 Read the book many details Courtship and Mating Breeding systems Sex Nests and Incubation Parents and their Offspring
Outline 1. Pair formation or other variations 2. Breeding systems 3. Nesting, Care of young 4. Fledging 5. Cooperative breeding
Types of Pair Formations Monogamous (14 % of socially monogamous species are also genetically monogamous) One male and one female Promiscuous Extra-pair copulations are the rule and not the exception (see Gill (2007, p. 361) Polygamous Many of one sex to one of the other Polyandry Polygyny
Monogamous Relationships Lifelong Geese, swans, eagles, albatrosses, petrels, gulls Different pairs each season Most passerines Different pairs with each brood House Wren, Bank Swallow Promiscuous Ruffed Grouse
Polygamous Relationships Polygyny - several females for each male Grouse, blackbirds Increased reproductive burden on female Polyandry- several males for each female Phalaropes, jacanas, tinamous Increases reproductive burden on males
Evolution of Polygyny Food availability where food is superabundant = polygyny Patchily distributed resources More common in relatively simple habitats (e.g., marshes & grasslands) Regular imbalance of sex ratios
Leks Resources (e.g., food or nest sites) are superabundant Resources unpredictable in Time Space Resources costly to defend Copulations performed by few males Always those that hold central positions in lek
Selection of Nest Site Usually completed by individual that is primary incubator Male may start several nests for female to choose between Perennial nests no new site selection between years (raptors, penguins and procellariids)
Nest Types Constructed nest Majority of nests Extremely varied Cup Dome Pouch
Nest Types Ground nest or scrapes Little or no construction Excavated nests Primary cavity nesters excavate their own cavity Secondary cavity use previously excavated cavities Burrows certain procellariids
Construction material Inorganic Mud/clay Stones Organic Woody material Fine grasses Hair Saliva Feathers Spider silk Snake skins
Australian Native Hen Megapode or Mound Builders
Australian Native Hen Incubation Mound - see Gill (2007, p. 463)
Tanimbar Scrubfowl - Indonesia
Forest Kingfisher nest
Buff-breasted Paradise Kingfisher
Why Build a Nest? Reduce predation risk 75-88% of nest losses due to predation Differential mammalian predation for ground nests Cavity nests are safest Protect eggs from weather
Eggs All birds form and lay shelled egg for external incubation Oviparity (Viviparity = retention of eggs & live birth) Embryos are intolerant of high temperatures Highly variable shape & coloration
Clutch Size Number of eggs laid in one set Subject to: Energy constraints Lifetime reproductive success Egg production is energetically costly 40-50% of basal metabolic rate for altricial hatchlings 125-180% of BMR for precocial hatchlings
Number of Clutches Most species will replace lost clutches once Some permanent residents always have > 1 clutch per year Mourning Dove in SE US will have up to 6 clutches per year Evolutionary tradeoff between lifetime reproductive success and life span
Incubation Maintain adequate temperature for development of embryo Most birds develop brood patch Loose feathers Existing apteria Some birds (e.g., lack apteria [penguins]) use feet for brooding Eggs are turned
Incubation Duties Varies among species and types of pair formation For most passerines both sexes incubate For most polygamous species, female incubates (except polyandry) Often elaborate relief ceremonies
Care and Development of Young
Stage of Development at Hatching Altricial (nest dweller) Young do not leave nest immediately Typically few if any feathers Relatively helpless Most passerines Precocial (nest fugitive) Can leave nest immediately Capable of locomotion Covered in natal down Some thermoregulatory dependence on parent
Brooding Continued thermoregulation of young by adult Especially important in altricial young Protects against hyper- & hypothermia Precocial young are brooded at night
Feeding of Young Responsibilities of 2 sexes differ among species With overlapping broods, males tend to do most Polygyny females do most Polyandry males do most
Nest Parasitism Do not incubate own eggs dump egg(s) in another species nest 5 families with obligate parasites 1 species of obligate nest parasite in North America Brown-headed Cowbird More than 100 species known to host cowbird eggs
Nest Parasitism Depresses nesting success Rates higher in fragmented habitats Young may evict eggs of host or kill host s young (European cuckoos)
Cooperative Breeding Defined by regular involvement of helpers in feeding and care of young Reported in about 300 species (3 % of species) Most species long-lived minimal loss of reproductive success to helper
Characteristics of Cooperative Breeding Habitat, territory or nest-site limitation Tropical or sub-tropical distribution Sedentary (relatively stable environments) Suitable habitat saturated part of population remain non-breeders Low fecundity Deferred maturity, high survival Population has relatively old age structure