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Parental Care IV: Incubation

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Parental Care IV: Incubation JodyLee Estrada Duek, Ph.D. With assistance from Dr. Gary Ritchison http://people.eku.edu/ritchisong/avianreproduction2.html – PowerPoint PPT presentation

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Title: Parental Care IV: Incubation


1
Parental Care IV Incubation
  • JodyLee Estrada Duek, Ph.D.
  • With assistance from Dr. Gary Ritchison
  • http//people.eku.edu/ritchisong/avianreproduction
    2.html

2
Incubation
  • During incubation, birds transfer heat to eggs.
  • For optimum development, egg temperature must be
    maintained at about 37 - 38 degrees C (Gill
    1995).
  • Exposure to higher temperatures is lethal, while
    cooler temperatures will, at minimum, slow down
    or stop development.
  • Heat is transferred through brood, or incubation,
    patches - an area of bare, flaccid skin on the
    abdomen and/or breast.
  • Prior to the initiation of incubation, the skin
    in the area of the brood patch loses its
    feathers.
  • In addition, the dermis becomes spongy and richly
    supplied with blood vessels (Welty and Baptista
    1988).

Arizona-Sonora Desert Museum
3
Brood patch
  • Birds of nearly all species temporarily shed
    their feathers on single or paired areas of the
    breast or abdomen early in the breeding season.
  • The bare skin increases in vascularity, which
    aids it in transferring body heat for incubating
    the eggs and brooding the chicks.
  • Development of these incubation (brood) patches
    is prompted by rising levels of estrogen.
  • They form in whichever sex cares for the eggs and
    young, usually females but often males as well.
  • The lost feathers are replaced in the complete
    molt following the breeding season (Stettenheim
    2000).

4
Incubation reduces microbial growth on eggshells
  • -- Avian eggshells harbor microbes shortly after
    laying, and under appropriate ambient conditions
    they can multiply rapidly, penetrate through
    shell pores, infect egg contents and cause embryo
    mortality.
  • Cook et al. (2005) experimentally examined how
    incubation affects bacterial processes on the
    eggshells of Pearl-eyed Thrashers (Margarops
    fuscatus) nesting in tropical montane and lowland
    forests in Puerto Rico.
  • Bacteria and fungi grew rapidly on shells of
    newly laid, unincubated eggs exposed to ambient
    conditions, but declined to low levels on shells
    of eggs incubated by thrashers.
  • Divergence in bacterial growth between incubated
    and exposed eggs was more marked at the montane
    forest than at the lowland site.
  • Pathogenic microorganisms became increasingly
    dominant on shells of exposed eggs, but these
    groups were relatively rare on incubated eggs,
    where more benign, less invasive groups
    prevailed.
  • Some incubation during laying may be necessary to
    decrease the probability of trans-shell infection
    by reducing the growth of harmful bacteria and
    fungi on eggshells, although it may increase
    hatching asynchrony and the likelihood of brood
    reduction.

5
Energetic cost of incubation
  • In birds, the annual peak of energy demand has
    long been thought to occur when parents provision
    their offspring with food during the nestling
    phase.
  • This led to idea selection on clutch size takes
    place during nestling phase.
  • energetic demands during other reproductive
    phases egg laying and incubation have been
    ignored.
  • During incubation, avian eggs need external heat
    provisioning, regular turning and favourable
    humidity for proper embryonic development care
    provided by one or both of parents.
  • energetic costs of providing heat to the eggs
    thought to be negligible.
  • Increasing evidence that below thermo-neutrality
    the metabolic rate (energy spent per time unit)
    of an incubating female is higher than that of a
    nonincubating female at rest.
  • Because temperatures are normally below
    thermoneutrality at temperate latitudes,
    energetic costs of incubation may substantially
    add to overall daily energy expenditure of
    attending parents.

6
Energetic costs of incubation
  • A nest-box modified into a metabolic chamber.
  • To ensure the top of the nest-box was airtight, a
    sheet of rubber was inserted between nest-box and
    lid (a) and a cork was placed in the entrance
    hole (b).
  • Reference air was measured close to the inflow of
    the nest-box (arrows underneath nest-box c),
    while sample air was drawn from the nest-box via
    a tube near the entrance hole (d).
  • The thickness of the nest was determined by the
    thickness of the nest cup (e) and the height of
    the nest rim (f).

7
Clutch size and incubation energetics
  • de Heij et al. (2007) manipulated the clutch
    sizes of female Great Tits (Parus major) and
    monitored their metabolic rates during nocturnal
    incubation using mobile oxygen analyzers.
  • found clutch enlargement caused incubating
    females to expend more energy, but clutch
    reduction did not lower energy expenditure.
  • absence of an effect of clutch reduction can be
    explained by a limit to number of eggs in direct
    contact with brood patch threshold clutch size
  • Above a threshold clutch size, eggs that are not
    in contact with the female's brood patch cool.
  • incubating birds will repeatedly rearrange eggs
    to rewarm
  • Rewarming energetically more costly than
    maintaining eggs at incubation temperatures.
  • energetic costs increase when clutch size is
    above the threshold clutch size, but do not
    change when clutch size is at or below threshold
    clutch size.

8
Nest insulation
  • de Heij et al. (2007) also found that incubating
    birds with thicker nests had lower energy
    expenditure, probably because thicker nests were
    better insulated.
  • The fact that not all birds build well-insulated
    nests suggests there is a cost to thick nests.
  • Knowing females expend more energy during
    nocturnal incubation when incubating
    experimentally enlarged clutches is a first step
    towards determining a potential mechanism
    underlying negative selection on clutch size
    during the incubation.
  • measurements on energy expenditure over a full 24
    h are needed to judge how important energy
    expenditure can be in explaining fitness
    consequences of incubating experimentally
    enlarged clutches.

9
Incubation
  • Most birds sit on their eggs to incubate, but
    there are exceptions.
  • For example, male Emperor (D. Attenborough clip)
    and King penguins place their egg on their feet,
    wrap their wing around the egg, and incubate it
    while standing up.
  • Male emperor penguins http//www.youtube.com/watch
    ?v6AiCIZ9wM1o
  • The egg is kept warm by the heat from the male's
    feet wing.

10
Foot-Mediated Incubation Nazca Booby (Sula
granti) Feet as Surrogate Brood Patches
Source www.mbr-pwrc.usgs.gov/id/framlst/Photo/p11
42.html
  • Incubation in most birds involves transferring
    heat from parent to egg through a highly
    vascularized brood patch.
  • Some birds, however, do not develop a brood
    patch.
  • hold their eggs under the webs of their feet
  • webs are often positioned between the feathered
    abdomen and the egg during incubation, suggesting
    that either the abdomen, the feet, or both could
    transfer heat to the egg.
  • Morgan et al. (2003) studied heat transfer from
    foot webs to eggs in Nazca boobies by spatially
    separating the feet from the abdomen using an
    oversized egg.
  • found feet transfer heat to eggs independently of
    any heat from the abdomen.
  • found that incubating boobies had significantly
    greater vascularization in foot webs, measured as
    percentage of web area covered by vessels
  • males, whether incubating or nonincubating, had
    significantly less vascularization
  • vascularized Nazca booby feet function during
    incubation as vascularized brood patches

11
Megapodes
Micronesian megapode
  • They are the only known birds which use heat
    sources, other than the body, to incubate their
    eggs.
  • When the young birds hatch they are fully able to
    defend for themselves and receive no parental
    care.
  • Megapodes are quite heavy-bodied birds and forage
    on the forest floor, where they search for
    insects, seeds and fruit.
  • All members of the Megapode family can fly, but
    most move around primarily by walking.

12
Megapode mound
  • found in Southeast Asia and Australia,
  • use heat sources
  • geothermal,
  • solar, or
  • decomposition of organic material.

13
Maleefowl 1
  • Maleefowl mound, Australia

14
Malleefowl 2
  • They spend up to eleven months of the year
    preparing, then maintaining, the mound adapting
    to daily, as well as seasonal, variations in
    temperature and rainfall.
  • mounds, made largely of sand raked up by their
    powerful feet, are each an immaculate circle
    approximately 4.5 metres in diameter.
  • This labour is to establish an exact and constant
    33oC - measured by its heat-sensitive beak - in
    the central chamber of the mound.
  • This chamber is literally carved out of
    consolidated layers of vegetation, like
    compressed paper mixed with sand.
  • All the eggs will be laid in this chamber - up to
    thirty at intervals of two to five days apart.
  • The key elements in incubation are solar heat and
    fermentation.
  • malleefowl make the most of rainfall and rely on
    daily raking of the mound to harness appropriate
    levels of solar energy.

15
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16
Malleefowl 3
  • In winter, when solar energy is minimal, they
    scratch together dead leaves, twigs, sparse humus
    and rake them into a path that leads directly
    into the now volcano-shaped centre of the mound.
  • It is not an uncommon sight to see a path of
    sticks and leaves, perhaps half a metre across
    and 20 metres long, leading from the bush up and
    over the side of the mound into its centre.
  • When wet, all the collected vegetation is sealed
    within the mound and buried to rot and ferment.
  • This process is repeated again and again and may
    take four months.
  • As the season warms and eggs are laid and buried,
    the malleefowl begin to uncover the mound,
    altering its architecture to reinforce the slow
    fermentation with the heat of the sun.
  • This process increases during the summer months
    until the mound itself is shaped like a pointed
    cone and the incubation process becomes dependent
    on solar energy alone.

17
Malleefowl 4 (Leipoa ocellata)
  • dedicate 9-11 months per year building and
    maintaining a large incubation mound of soil,
    leaves and twigs.
  • The eggs are laid in the mound, buried and left
    to incubate by heat generated from the composting
    litter.
  • Malleefowl mounds may be used over many
    generations and can attain an impressive size of
    22 meters in circumference and 1 meter high.
  • The birds maintain the mound temperature of 32-34
    degrees C by using their beak as a "thermometer"
    and adjusting soil cover to either retain or
    expel heat from the egg chamber. 'Incubation'
    typically takes 60 - 90 days.

(Sourcehttp//www.malleefowl.com.au/Pages/TheMall
eefowl.htm)
18
Incubation periods
  • range from about 10 days for some passerines
    woodpeckers to as many as 80 days for albatross'
    and kiwis.
  • time spent incubating is related to the size of
    the egg, state of development (precocial vs.
    altricial), ambient temperature.

Temperatures in an Eastern Bluebird nest cup in
Texas (Cooper and Phillips 2002).
19
Nest predation appears to affect parental
behavior 1
  • Based on an analysis of incubation and
    provisioning behavior of 97 species of
    passerines, Conway and Martin (2000) suggested
    environments with high risk of nest predation
    favor long on-bouts (long periods on nest) and
    few foraging trips.
  • This strategy may prevent frequent feeding by
    adults and thus compromise future reproductive
    attempts.
  • nest predation may influence evolution of avian
    life-history traits in several ways.
  • High nest predation favors a strategy of
  • holding back reproductive effort for renesting
    attempts and survival,
  • a short nesting cycle to minimize the time nests
    are susceptible to predation,
  • small brood size to minimize noise of begging
    young 

20
Nest predation appears to affect parental
behavior 2
  • Conway and Martin (2000) suggest nest predation
    may influence passerines by placing constraints
    on parental activity and the way an incubating
    female allocates her time between incubation and
    foraging.
  • with high nest predation, natural selection
    simultaneously favors infrequent nest trips (to
    reduce the probability of predator detection) and
    short off-bout duration (to maximize development
    rates and reduce time of exposure to predators).
  • These somewhat opposing constraints limit the
    range of effective incubation strategies
    available to females in environments with high
    nest predation. 

21
Males Feeding Females during Incubation 1
  • See graph on following slide of nest
    attentiveness (percentage of time that the female
    is incubating on the nest) relative to the rate
    that males bring food to the nest (incubation
    feeding).
  • The relationship across 19 species of both open-
    and cavity-nesters is curvilinear and
    significant.
  • Nest attentiveness (percentage of time spent on
    the nest) during incubation represents a
    parent-offspring conflict incubating birds must
    trade-off between caring for embryos by staying
    on the nest versus caring for themselves by
    getting off the nest to forage.
  • For species in which females are the sole
    incubator, males can potentially affect this
    trade-off and increase nest attentiveness by
    feeding incubating females on the nest
    (incubation feeding).
  • (From Martin and Ghalambor 1999).

22
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23
Males Feeding Females during Incubation 2 Theory
(Martin and Ghalambor 1999)
  • Increased nest attentiveness may be required when
    local microclimate is harsh and requires more
    incubation feeding (microclimate hypothesis).
  • Incubation feeding may be constrained by risk of
    attracting nest predators (nest predation
    hypothesis), which in turn may constrain female
    nest attentiveness because of energy limitation.
  • incubation feeding rates are greater among
    cavity-nesting than open-nesting birds.
  • Under microclimate hypothesis, the greater
    incubation feeding rates of cavity-nesting birds
    generate the prediction that microclimate should
    be harsher than for open-nesting birds.
  • results reject this hypothesis because we found
    the opposite pattern cavity-nesting birds
    experienced more moderate (less variable)
    microclimates that were less often below
    temperatures (i.e., 16C) that can negatively
    impact eggs compared with open-nesting species.
  • In contrast, incubation feeding rates were highly
    negatively correlated with nest predation both
    within and between the two nest types, supporting
    the nest predation hypothesis.
  • Incubation feeding in turn was positively
    correlated with nest attentiveness.
  • Thus, nest predation may indirectly affect female
    incubation behavior by directly affecting
    incubation feeding by the male (Check this short
    video of a male Blue Tit feeding his mate).

24
Food availability and nest attentiveness across
species and latitudes Chalfoun and Martin (2007)
  • Both northern and southern species are expected
    to show proximate increases in attentiveness in
    response to increased food availability,
  • preliminary data further suggest that northern
    species show slightly stronger responses.
  • Proximate responses to food availability alone,
    however, cannot explain why southern species
    generally show lower nest attentiveness than
    similar northern species (grey arrows).

25
Latitudinal variation in avian incubation
attentiveness 1
  • Avian incubation attentiveness has important
    fitness consequences
  • number of young
  • quality of hatched young
  • energetic costs imposed on parents.
  • Nest attentiveness is highly variable across
    species and geographical regions.
  • Chalfoun and Martin (2007) reviewed the
    literature and found a worldwide pattern that
    nest attentiveness of passerines is generally
    lower in south temperate and tropical regions
    than in north temperate regions.
  • conducted a food manipulation experiment to
    assess nest attentiveness does it reflect
    proximate responses or an evolved behaviour.
  • Karoo Prinia (Prinia maculosa) in South Africa
    has very low nest attentiveness (about 49)
    compared with many passerines.
  • provided supplemental food during early
    incubation to experimental females and compared
    nest attentiveness and on- and off-bout lengths
  • Nest attentiveness of females at food-provisioned
    nests was significantly higher than control
    females (57 vs. 49).
  • Food-supplemented females spent significantly
    less time off nest than did control females mean
    on-bout lengths did not differ.

26
Latitudinal variation in avian incubation
attentiveness 2
  • mean nest attentiveness of food-provisioned
    females still substantially below similar species
    worldwide.
  • Food can be an important proximate influence on
    parental care behaviour, but proximate influences
    of food do not explain latitudinal patterns of
    attentiveness.
  • Climatic variation across latitudes may influence
    the amount of time that parents spend on the
    nest, although temperatures at many south
    temperate sites often approximate those at north
    temperate sites during the breeding season.
  • One possible alternative explanation for
    geographical patterns in nest attentiveness is
    variation in adult mortality across latitudes.
  • According to classic life history theory, if
    southern birds experience lower adult mortality,
    they should be less willing to invest as much in
    nest attentiveness and other components of
    current reproduction.
  • Testing for the existence of an adult
    mortalitynest attentiveness trade-off across
    latitudes is therefore a critical next step in
    addressing geographical variation in parental
    care strategies.

27
Winter habitat influences reproductive success 1
  • destruction of tropical forests is creating
    breeding problems for migratory birds.
  • Norris et al. (2004) found quality of winter
    habitat affected ability of American Redstarts to
    successfully reproduce when they returned north
    in the spring.
  • Norris,noted that a relatively small geographic
    band across the Caribbean, Greater Antilles,
    and central America is the annual destination
    of an estimated five billion migratory birds
    flying south each year from Canada.
  • Norris et al. (2004) measured stable carbon
    isotopes in blood samples collected from American
    Redstarts after the birds arrived at their
    breeding grounds in Ontario.
  • Since the turnover time of the blood cells is
    from six to eight weeks, they provide a good
    indicator of the quality of the birds' previous
    habitat on the wintering ground.
  • The carbon signature of each redstart has been
    deposited by insects the bird ate, and the
    insects in turn fed on vegetation growing in the
    winter habitat.
  • Its a 'food chain signature'

28
Winter habitat influences reproductive success 2
  • Norris et al. (2004) first determined high and
    low quality habitats for redstarts, which winter
    in the Caribbean and central America, and breed
    in deciduous forest throughout Canada and the
    U.S.
  • what makes a better winter habitat is primarily
    the degree of wetness, particularly at the end of
    the season (late winter/early spring) when low
    quality habitats tend to dry out.
  • The second step was to develop isotope "markers"
    that identify habitat quality for each type of
    habitat.
  • Third, blood samples were taken from warblers in
    their breeding grounds
  • Fourth, the birds' reproductive success was
    measured by counting the number of "fledged"
    offspring to leave their nests.
  • Analysis revealed that redstarts wintering in
    high quality habitats, such as mangroves and
    lowland tropical forests, arrived earlier on the
    breeding grounds, nested earlier, and were more
    successful in producing young.
  • This study shows that destroying high quality
    winter habitat has a disproportionate effect on
    the redstart populations they lose the areas
    most capable of supporting them. 

29
Eggshell
  • protects the embryo
  • generally white in cavity-nesters colored and
    patterned in open nesters (for camouflage)
  • color is added to the eggshell from pigments
    secreted by cells in the wall of the uterus
  • contains thousands of pores (see diagram) that
    permit gas exchange

Thousands of tiny pores like the ones pictured,
cover the shell, providing a passage for gas
exchange. (Source http//www.rit.edu/tld0898/SE
M.html)
30
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31
Eggshell pores
  • An egg must exchange gases with its environment
  • This allows for the removal of excess CO2 and the
    influx of fresh air with additional O2 as gases
    diffuse through pores in the eggshell
  • Water loss also occurs through these pores
  • Water loss leads to a larger and larger air
    chamber at the blunt end of the egg
  • Just before hatching the chick needs to inflate
    its lungs and breathe
  • This is accomplished as the chick breaks the
    membranes and has access to the air chamber at
    the blunt end of the egg
  • There is a fine line between
  • not having enough air in the chamber to allow the
    chick to breathe long enough to break a hole in
    the shell
  • losing too much water and the embryo dehydrating
    before maturity
  • The rate, and total amount, of water loss depends
    on
  • Ambient temperature
  • Humidity
  • Elevation and subsequent air pressure

32
Egg water vapor conductance
  • AR AND RAHN and others at SUNY Buffalo measured
    the water vapor conductances of fresh eggs of 29
    species
  • showed how this total value increases with egg
    weight.
  • change in egg shell thickness with egg weight
    also determined from the literature
  • measured periodically the weight loss under known
    conditions of temperature, humidity, and
    barometric pressure
  • rate of water loss per gram egg weight decreases
    as the eggs get larger large eggs can save more
    water than small eggs.

33
Incubation period and water loss
  • Both Needham (1931) and Romanoff and Romanoff
    (1949) noted that species with large eggs tend to
    have longer incubation periods and thus would be
    exposed longer to water losses.
  • This problem is discussed in detail by Rahn and
    Ar (1974) who showed that the extended incubation
    period in larger eggs is compensated for
    perfectIy by the reduction in water vapor
    conductance per unit egg weight which they
    express as a common water loss coefficient for
    all eggs.
  • Whether the increase in pore area with weight is
    achieved by increasing the number of pores or
    their diameter or some combination of the two is
    still being explored.

34
Eggshell pores http//www.cooper.org/pdf/p1977Rahn
1974.pdf
  • Gas exchange in the avian embryo has been shown
    to be dependent on, and limited by, the diffusive
    properties of gases across the resistance offered
    by the shell and shell membranes
  • The diffusive rate of water loss from eggs
    depends on
  • permeability constant of the shell
  • Pore size
  • Number of pores per unit area
  • surface area of the shell ( cm2)
  • water vapor pressure difference across the
    eggshell

35
Maculation in eggshells James P. Higham  and
Andrew G. Gosler 2006 Oecologia
  • Many small passerine birds worldwide lay white
    eggs speckled with red, brown and black
    protoporphyrin pigment spots (maculation).
  • Unlike some patterns of avian eggshell
    pigmentation which clearly serve a crypsis or
    signalling function, the ubiquity of maculation
    among passerines suggests that its origins lie in
    another function, not specific to any particular
    ecological or behavioural group.
  • There is evidence that protoporphyrin pigments
    serve a structural function related to eggshell
    thickness and calcium availability eggshell
    maculation in the great tit Parus major increases
    with decreasing soil calcium levels, pigments
    demarcate thinner areas of shell, and both the
    pigment intensity and distribution are related to
    shell thickness.
  • maculation also affects the rate of water loss
    from the egg during incubation ( Mass Loss per
    Day or MLD, which is critical to egg viability),
    but not that of unincubated eggs.
  • They demonstrate, both by observation and
    experiment, that the effect of female incubation
    behaviour on MLD compensates in some way for
    variation in egg characteristics, and that
    differences between females in the degree of such
    compensation are related to differences in clutch
    maculation.
  • results suggest that, while a principal function
    of maculation in this species may be to
    strengthen the eggshell, it may also reduce
    eggshell permeability when large amounts of
    pigment are used, and that this necessitates a
    behavioural adjustment from the female during
    incubation.

36
Condor, 1987
A special problem with mount nesters and gas
exchange
37
Elevation and water loss
  • Among species found at wide ranges altitudinally,
    there is a local variation in number of eggshell
    pores per unit area, OR in size of individual
    pores
  • Higher elevation results in more rapid diffusion
    therefore fewer pores, or smaller pores, are
    needed
  • Birds that are moved altitudinally fairly quickly
    adjust pore numbers and/or pore sizes in the eggs
    that they lay

38
Adaptation of the Avian Egg to High Altitude
1 CYNTHIA CAREY American Zoologist 1980
  • Theoretical predictions and experiments on eggs
    of domesticated birds indicate that the diffusion
    coefficient of gases is inversely proportional to
    barometric pressure.
  • Therefore potentially lethal losses of CO2 and
    water vapor from eggs laid at high altitude might
    result if the increased tendency of gases to
    diffuse at reduced barometric pressure were not
    counteracted
  • data from two wild populations indicate water
    loss is independent of altitude over a 3000 m
    gradient.
  • Four different possibilities by which
    compensation for increased diffusion of water
    vapor might be achieved at high elevations
  • 1) a reduction in eggshell conductance (GH2O)
  • 2) an increase in the initial water content of
    the eggs
  • 3) an increase in shell thickness
  • 4) alteration of water vapor pressure in the nest
    microenvironment or incubation temperature by
    variation in parental behavior

39
Adaptation of the Avian Egg to High Altitude 2
  • Mean GH2O of eggs of two precocial and four
    altricial species breeding above 2800 m is
    significantly reduced below values of related
    birds breeding at lower elevations, but no change
    in initial water content or shell thickness has
    been observed in such eggs
  • That data contradicts hypotheses 2 and 3
  • Observations of parental behavior in species
    breeding over wide elevational gradients have not
    yet been made (hypothesis 4)
  • More research needed for identification of the
    mechanisms
  • ways eggshell structure is modified to achieve a
    reduced GH2O
  • environmental cues used by females to determine
    elevation of nest location
  • the rapidity with which shell structure can be
    modified

40
Elevation and water loss H. Rahn, T. Ledoux, C.
V. Paganelli and A. H. Smith J Appl Physiol 53
1429-1431, 1982 8750-7587
  • Hens acclimated to an altitude of 3,800 m (PB 480
    Torr) were transferred to 1,200 m (PB 657 Torr).
  • Eggs were collected before departure and daily
    after the transfer so that changes in eggshell
    conductance could be studied.
  • Over the next 2 mo eggshell conductance increased
    30, presumably to compensate for the 37
    reduction (from 657 to 480 Torr) in gas
    diffusivity at the lower altitude.
  • Measurements of shell thickness and number of
    pores in the shell allow one to calculate that
    most of the change in total pore area occurred by
    an increase in cross-sectional area of individual
    pores.

41
Altitude and eggshells Monge-C. and
F. León-Velarde (1993)  
  • At the end of incubation, partial pressures of
    oxygen and carbon dioxide in the air cell of
    sea-level avian eggs are similar to those in the
    expiratory air of adult birds.
  • At high altitude, changes in the permeability of
    the shell and probably in embryo metabolism
    partially compensates the increase in the gas
    diffusion constant resulting from the low
    barometric pressure.
  • tested whether-despite of the adaptive responses
    of the high altitude avian embryo-the air cell
    values would be similar to those of the alveolar
    air of high altitude human natives.
  • Air cell O2 (48.31.6 torr) and CO2 (20.90.85
    torr) pressure values were obtained by studying
    naturally incubated eggs of the Andean gull
    (Larus serranus) at 4650m.
  • Sea-level chicken (Gallus gallus) air cell
    pressure values of O2 (102.32.7 torr) and of CO2
    (43.31.3 torr) were obtained from the literature
    for comparison.
  • values similar to alveolar air of humans at sea
    level (O2 104.40.4 torr, CO2 40.1 0.25 torr)
    and at high altitude (4540 m) (O250.50.53 torr,
    CO2 29.10.37 torr).
  • Despite large evolutionary changes in morphology
    and physiology of respiratory organs, head
    pressure of O2 that oxygenates the blood keeps a
    constant value in the pre-pipping avian embryo
    and in alveolar air of adult mammals.
  • This constancy holds valid at high altitude.

42
Differences in egg size, shell thickness, pore
density, pore diameter and water vapour
conductance between first and second eggs of
Snares Penguins Eudyptes robustus and their
influence on hatching asynchrony MELANIE
MASSARO, LLOYD S. DAVIS (2005) Ibis 147 (2) ,
251258
  • Brood reduction in birds is frequently induced by
    hatching asynchrony.
  • Crested penguins (genus Eudyptes) are obligate
    brood reducers, but in contrast to most other
    birds, first-laid eggs are considerably smaller
    in size than second-laid eggs furthermore,
    first-laid eggs hatch after their siblings
  • The mechanisms underlying this reversal in size
    and hatching order remain unclear.
  • tested whether the second-laid eggs of Snares
    Penguins have a higher eggshell porosity allowing
    them to maintain a higher metabolic rate
    throughout incubation and to hatch before their
    first-laid siblings.
  • investigated differences in egg size, shell
    thickness, pore density, pore diameter and water
    vapour conductance between first and second eggs
    within clutches and examined influence of shell
    characteristics on hatching asynchrony.
  • First-laid eggs were approximately 78 the size
    of larger second eggs.
  • Second-laid eggs had considerably thicker shells
    and more pores per cm2 than first eggs pore
    diameter did not differ

43
Differences in egg size, shell thickness, pore
density, pore diameter and water vapour
conductance between first and second eggs of
Snares Penguins Eudyptes robustus and their
influence on hatching asynchrony MELANIE
MASSARO, LLOYD S. DAVIS (2005) Ibis 147 (2) ,
251258
  • Water vapour conductance was greater in second-
    (16.8 mg/day/torr) than in first-laid eggs
    (14.9 mg/day/torr).
  • The difference in water vapour conductance
    between first- and second-laid eggs within
    clutches was related to hatching patterns.
  • In nests where second eggs hatched before
    first-laid eggs, second eggs had a considerably
    greater water conductance than their sibling,
    whereas in nests where both eggs hatched on the
    same day, the difference in water conductance
    between eggs was very small, and in a few nests
    where small first eggs hatched before their
    larger sibling, they had a greater water
    conductance than their larger second-laid
    nestmate.
  • Surprisingly few studies have investigated
    differences in shell characteristics between eggs
    within clutches and associated effects on
    hatching asynchrony.
  • This study has demonstrated that such differences
    exist between eggs within clutches and that they
    can influence hatching patterns.

44
EGG SIZE, EGGSHELL POROSITY, AND INCUBATION
PERIOD IN THE MARINE BIRD FAMILY ALCIDAE Karen
Zimmermann and J. Mark Hipfner The Auk
  • ultimate factors that influence duration of avian
    incubation are well known, we know much less
    about the proximate mechanisms by which birds
    adjust incubation period
  • tested the hypothesis that an adjustment in
    eggshell porosity is one such proximate mechanism
    (i.e., that avian species with higher ratios of
    incubation period to egg size lay eggs with less
    porous shells).
  • Eggshell porosity affects the rate of gaseous
    exchange between the developing embryo and the
    external environment thus, to the extent that
    embryonic metabolism is diffusion-limited,
    eggshell porosity could directly determine
    incubation period.
  • collected eggs from seven species of Alcidae, a
    family of marine birds that exhibits an unusual
    degree of interspecific variation in incubation
    period, and measured egg mass and eggshell
    porosity (determined by the number and size of
    pores and the thickness of the shell). Incubation
    periods were obtained from the literature.
  • Egg mass and eggshell porosity combined explained
    87 of variation in incubation period among the
    species, which included at least one member of
    each of six main alcid lineages.
  • As predicted, eggshell porosity and incubation
    period were negatively related, after controlling
    for egg mass.
  • results are consistent with the hypothesis that
    evolutionary changes in avian incubation period
    may be attributed, at least in part, to
    adjustments in eggshell porosity.

45
Canada goose hatching
  • http//www.youtube.com/watch?vTYJiQ-03tBI
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