week 9 - birds cont. Flashcards
birds and reproductive strategies
- Reproduction has evolved to maximise breeding success through energetic and temporal investment
- Breeding success = output of each year (i.e. no. of offspring) summed over the total years in which he/she is reproductively active
- Informed of ‘health’ of individuals, populations and habitats
- Varies between males and females
birdlife international statistics
- One in eight of the world’s bird species is globally threatened with extinction
- 128 ssp. Became extinct in the last 500 years
- Ssp. Of the above since 1800
- Some species will disappear before we know anything about them
copulation
- A brief encounter
- Allows sperm to fertilize eggs
- Lasts 1-2 seconds and then it is over
o Very quick
o Male and female face each other
o ‘kiss’
courtship feeding
- Males feeds female and thereby demonstrates his foraging ability
- Also shows that he can provide for chicks
- Feeding often initates mating when female has ovulated and is receptive
Gift (food parcel)
Courtship feeding - Good at finding food
- Proves that he can provide to chicks
Hormones activates and female ovulates
Lekking behaviour
- Seen in grouse and waders
- Often occurs in species where promiscuous males compete for matings
- Females visit the lek to seek fertilisations with the ‘best’ males
Elaborate dance
Demonstrating good genes - Also how they look
Better health better red cone - Secondary sex signals
sperm competition
- Sperm stores by female in sperm-storage tubules
- In domestic chicken (Gallus gallus) sperm viable for 7 to 14 days
- Sperm released from sperm-storage tibules after ovulation
- After successive inseminations, no-mixing of sperm but sperm function on a last in first out principle
how does female control sperm release and thus paternity of offspring?
egg formation
- Sperm fertilise ovum in the infundibulum
- Ovum passes down the reproductive tract receiving layers of albumen (water and protein) in process called ‘plumping’
- ‘plumped’ egg calcified in the ‘uterus’ or shell gland (takes about 12 hours)
- Eggs laid normally once every 24 hours
o Usually in the morning to get rid of the weight
the avian breeding cycle
—> RECRUITMENT (becomes a member of breeding population
–> EGG LAYING
–> INCUBATION (sits on eggs)
–> CHICK REARING
–> FLEDGING (very vulnerable to predators)–> RECRUITMENT
social mating systems
monogamy
social polygyny
social polyanndry
social mating systems
monogamy
o One male and one female in pair
o 85% of all species including most passerines
social mating systems
social polygyny
o One male and many females
o Occurs in approx. 10% of species
o Female tends offspring and male deserts (one nest to the other)
social mating systems
social polyandry
o One female and many males
o Occurs in 11 families
o Males tends offspring and female deserts
o More rare (penguins)
reproductive strategies
Ornithologist study 3 types:
- Social
o Two birds defend a breeding territory and/or provide parental care
- Sexual
o Two birds pair to copulate
- Cooperative
o More than 2 birds care for a single brood of offspring
david lack (1968)
- monogamy as system of choice?
“monogamy in birds and men, tends to be dressed in drab colours, but is far more frequent than the exotic”
- Monogamy as the system of choice
Wrong on this occasion
(lack still shapes the way that modern ornithologists think)
- Molecular techniques have provided answers that lack did not have at his disposal
- Social bonds are not sexual bonds
o Of socially monogamous species studied with DNA fingerprinting techniques, >85% of them are sexually polygamous
- Extra pair copulations (EPCs) appear to be the most prevalent mechanism driving extra-pair paternity (EPP)
o Paternity outside social pairs
sexual mating systems
Variation in sexual mating systems measured with extra-pair offspring as the unit
EPP can arise from:
- EPCs – female mates with >1 male other than social male
o Australism running fern (everyone copulates with everyone) - Intraspecific brood parasitism (IBP) – conspecific female lays egg(s) in another female’s nest (egg dumping)
o Social male dies
o Gives her eggs a fighting chance
o Wood duck - Rapid mate switching – pair-female lays eggs fertilized by previous social male
All of this can lead to male uncertainty of paternity
cooperative mating systems
- Occurs in approx. 3% of species including kingfishers , hawks and jays
- Large family group, usually of related members, but only one breeding pair
o Other family members are called helpers - Included in the group is the polygynandrous Dunnock (Prunella modularis).
o >2 group members copulate and contribute to the breeding attempt in an uneasy truce where all offspring are raised by males as they are uncertain which chicks are theirs
Cooperative mating systems
florida scrub-jay (FS-J)
FS-J breeding success with age
- ring every bird in pop. breeding experience is key
there is an advantage to helpers
Adult female behaviour
- Common Cuckoo female removes host egg
- Eating egg provides her with nutrients
- Her egg’s spotting pattern must match closely with that of host’s if she is to avoid being detected
Chick behaviour
- 1- or 2-day old chick evicts host’s eggs from nest
- Successful because cuckoo egg hatches prior to host’s
- Chick then receives all the food
Eggshell pigmentation
- Pigments from breakdown of blood
- Unlikely to be a defence against common cuckoos etc. in all cases
- In Great Tits (Parus major) pigment patterns inherited from maternal grandmothers to mothers and then to daughters
- Thus, functionally significant but how?
Colony nesting
- Synchronised breeding
- Lowers predation risk
- Information centre but what type of information exchanged?
Communal nesting
- All females lay in the same nest
- Occurs in anis (Crotophaga spp.) a New World cuckoo
- 20 eggs can be laid in one nest
- Often eggs (and chicks) are tossed from nest by contributing females
- In the smooth-billed Ani (crotophaga ani), early laid eggs are tossed by later layers, the socially dominant females
Who incubates?
- Male only
o Emperor penguin (Aptenodytes forsteri), Kiwis, Emu (Dromaius novaehollandiae) - Female only
o Most passerines, pheasants, ducks - Both sexes
o Pigeons, antbirds, warblers - Neither sex
o Megapodes (Megapodius spp.), exclusive brood parasites (e.g. cowbirds [Molothrus} spp.)
E.g. the mound of vegetation
Creching behaviour
- Creches form in penguins, shelducks (tadorna tadorna) etc.
- From when parents stop chick-guarding and disperse widely to forage
- In penguins a creche can number a few (e.g. Gentoo penguins [Oygoscelis papua]) to many thousands of chicks (e.g. king penguins [Aptenodyres patagonicus])
- Protects chicks from predator attack and allows them to keep warm
Brood partitioning
- Clutch size determined by number of chicks that parents can feed
o Lack’s hypothesis - Brood partitioning might maximise chick survival
- In common blackbirds (Turdus merula) each parent looks after half of the brood
- All chicks may be lost if remain as one group that succumbs to a predator attack
