Lectures
25-27 - Populations and Demography
20-24 March, 2000
|
Age |
Sx |
Lx |
Bx |
LxBx |
|
0 |
0.305 |
1.000 |
0 |
0.000 |
|
1 |
0.594 |
0.305 |
1.04 |
0.317 |
|
2 |
0.632 |
0.181 |
1.3 |
0.236 |
|
3 |
0.667 |
0.114 |
1.3 |
0.149 |
|
4 |
0.75 |
0.076 |
1.3 |
0.099 |
|
5 |
0.75 |
0.057 |
1.3 |
0.074 |
|
6 |
0.75 |
0.043 |
1.3 |
0.056 |
|
7 |
0.75 |
0.032 |
1.3 |
0.042 |
|
|
|
|
|
0.973 |
Varies greatly among
individuals
a few females contribute
most young to next generation
Screech Owls
Albatross
European Sparrowhawk
(see review by Ian Newton)
IV.
Annual survival
varies 30% - 95%
over time
between sexes and species
between regions
trends
large>small
seabirds>landbirds
tropical>temperate/arctic
fledgling half that of
adults
males>females
not well understood
leads to biased sex ratio
supports notion of cost of reproduction
best data from Sparrowhawk
nests in Wytham Woods
nearly 1000 rings from banded (ringed) tits found in nest/yr
18-34% of juvenile Great Tits
18-24% of juvenile Blue Tits
condition of females
Adults much higher –
1.
Herring
Gulls: S1 60%, S>1= 90%
2.
Great Tits:
S1 20%, S>1 48%
Longevity
small birds 2-5 yrs
but tropical species longer
records 10-20 yrs
Adelie Penguins average 20 yrs
34 yr-old Frigatebird
36 yr-old Eurasian Flycatcher
Royal Albatross in New Zealand at least 58 yrs
Captive birds longer -
parrots up to 80 yrs.
Sources of mortality:
Not well documented
Starvation, disease, predation, climate (2000 winter freeze killed a
lot of kinglets in E. NC
Some data for human-induced mortality in the 70s:
270 million killed (but <2% OF 10-20 billion birds in continental
US)
hunting – 270 MM
Pest control – 2 MM
Road kills – 57 MM
TV towers – 1.2 MM
Windows – 80 MM
90s data – 200 MM killed by domestic cats!
Young have two phases of mortality
Clumsy phase just after fledging – predators
Starvation after adult provisioning ends
V.
Fecundity
redefine = # young successfully raised
annual vs. lifetime
annual most affected by conditions that year
# nests/year
experience of female
lifetime
age at first reproduction
lifespan
what affects it?
Multiple broods
more common in tropics
breeding season longer
more predation
6 clutches/yr not uncommon
longer between attempts in tropics
food limitation?
more extended parental
care
not possible with extended parental care
can be overlapping (Rock Doves) -Barn Owls?
Nesting success
> away from tropics
> in hole nesters
> in large species “with hardy young”
causes:
predation
starvation
desertion
hatching failure
weather
brood parasites
nest-site competition
ectoparasites
disease
Clutch size - the 64K question to students of life history
heritable
nutritional limits on females for precocial species
feeding abilities for altricial
range 1-20
varies in some species
fixed in
Pelecaniformes
(not so!) 1 egg
Procellariiformes
1 egg
hummers
and doves = always 2
Age and experience
Delayed breeding
most breed at 1 yr, but some 2,3, even 8-12 yrs - why?
must be cost of early breeding
Good figures for Adelie
Penguins
survivorship
breeders 61% non 78%
75%
3 yr olds die first attempt
this
declines to 10% of 11-yr olds
birds that did breed in 3rd yr do better subsequently than
those that didn’t
because experience needed
male passerines don’t always attain breeding plumage
in 1st yr - 31/105 dimorphic NA passerines
e.g.
Red-winged
Blackbirds
Northern
Orioles
Scarlet
Tanagers
American
Redstarts
often can and do breed-e.g.
American Redstarts
avoid hassles with adult males
reduced
predation?
substandard
territories
VI.
Evolution of clutch size
Lack’s food limitation
hypothesis -
max number the parents can feed and raise - supported by clutch
manipulation studies - show overhead-Fig 20-7
Empirical evidence shows latitudinal increase in
many passerines
owls
hawks
herons
terns
gallinules
some fowl
some grebes
Lack says day length a
factor
which group above doesn’t this make sense for?
weaknesses
observed variation across
longitude
islands < mainland
high alt > low (only in
temp. zone)
owls
some birds have been shown
to be able to raise more young in clutch enhancement studies
Trade-off hypothesis
seems to work for larger
species - increased clutch size reduces survivorship
not for some smaller
species
Predation
longer to lay large clutch
- increase exposure
larger broods more
conspicuous
better to risk fewer
eggs/attempt in predator rich environment
ability to defend and feed
young fledged may be limiting factor
Seasonality
population regulated in
non-breeding season
resources abundant in
breeding season
surplus -> young
Murray’s theory
females minimize
clutch size to level of replacement
increases survivorship
fits empirical evidence very well
Brood reduction
insurance against bad
years
lay eggs of different quality
siblicide-Cain & Abel - opportunity for conservation?
begin incubation with last egg = unequal feeding
reduces demand even in
good years
balances sex ratio in
RWBlackbirds
young
females raise fewer males
males need more food
young moms less efficient providers
old females produce more
males for unknown reasons
