lecture 13: avain demography

Avian Demography

Study of characteristics of populations-age, reproductive output, mortality

Purpose of demography

Management and conservation for life history theory

R

Number and survival of young fledged each year

K

Individual survival

Example of R selected species

Duck, grouse

Example of k selected species

Auk, sheerwater

Total population size

Number of breeding pairs or females→ generally unknown

Methods of population surveys

• Direct counts (by photographing)

• Breeding bird survey- long term sample of population

• Capture-mark/recapture

• Migration monitoring

Mortality

Carcass count x (1/detection rate)

Detection rate

Proportion of dead individuals found

Stable population equation

Births + immigration = deaths + emigration

Life History

The schedule of activity in a bird’s life that maximizes reproductive success

R-selected species

Produce lots of young but live a short time. → mallard, blue tit

K-selected species

Love a long time, produce less young. → thick-billed murre

Number of birds observed in year two

= number banded in year one X survival rate X recapture rate

Survival rate

= number banded /(number recaptured x recapture rate)

Fecundity

The number of young successfully raised per year

→ determined by: breeding attempts, clutch size, breeding success

Phenology

Timing or clutch initiation that varies with latitude

Senescence

Age related deterioration due to cellular deterioration and accumulated mutations

Lack’s hypothesis

The clutch size in birds is adjusted by natural selection to the maximum number of nestlings the parents can nourish

Trade-off hypothesis

The clutch size is adjusted by natural selection to optimize reproductive success through a balance between current clutch size and future survival

Biggest effect on nestling survival

Starvation

Bird sex ratio

50/50

Exception to typical sex ratio

• Tree swallow: females in better conditions produce more males

• American kestrels: seasonally different ratio per season

• Blue tit: females mated to attractive males produce more sons