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Afghanistan field and training manual - Micronutrient Initiative

By Janice Hunt,2014-09-30 13:35
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Afghanistan field and training manual - Micronutrient Initiative

    Matt Johnson

    HSU Wildlife 365

    Ornithology

    ORNITHOLOGY

    (Humboldt State Univ. WILDLIFE 365)

    LECTURE 18 NESTS AND INCUBATION

    I. Introduction.

     No birds bear live young. Instead, they prepare a nest to cradle their eggs and young. The risks associated with nest building and egg/young care are great; thus, evolutionary pressure has resulted in myriad solutions to diverse demands of insulation, crypsis, and energetic costs associated with nest-building and incubation.

    II. Nest Architecture.

    A. Nest types.

    1. There are a truly phenomenal number of nest types out there.

    And many still remain to be discovered. Marbled Murrelet

    nests were discovered until 1974 -- in Santa Cruz. Only 10

    described by 1987...now it's endangered.

    2. Bird nests vary from: OVERHEAD

    1. Floating mats

    2. Open scrapes

    3. Cavity nests

    4. Stick nests

    5. Colonial mud nests.

    6. Open cup nests.

    7. Hanging, woven nests.

    B. Nest Materials. Likewise, a variety of nest materials are used.

    1. Most birds use at least plant materials:

    a. Sticks and twigs - common especially in larger arboreal

    nesting birds.

    b. Reeds and grasses -- common especially in species that

    weave nests.

    c. Green vegetation -- especially important in controlling

    ectoparasite populations.

    2. Others do not.

    a. Spiderwebs -- hummingbirds and others who suspend

    nests.

    b. Mud.

    c. Sand/rocks -- many shorebirds simply scrape a place on

    the ground for their eggs.

    3. Nets linings/"decorations"

    a. Many species line their nests with unique materials to aid

    in thermoregulation or crypsis.

    b. Lichen, feathers, bark on outside of nest for crypsis.

    c. Down, mammal hair, moss for insulation as nest lining.

    C. Nest Building.

    1. Who does it? -- Can be either or both sexes. In many

    polygynous birds, only the female builds a nest. In many

    monogamous birds, both species build. In some, such as the

    Marsh Wren, males build many potential nests, among which

    the female chooses. A major criterion for females in mate

    selection is a male's nest-building skill.

    2. How do they do it?

    a. Most use primarily bill, but feet and body occasionally

    used as well, especially for earth burrowers.

    b. Bill most adapted for feeding, not as strongly influenced

    by nest-building requirements. Nonetheless, a birds bill

    is used variably as pliers, needle and thread, tweezers,

    hammers, plasterer's tool, shovel, etc.

    c. Weavers have the most advanced nest-building skills,

    demonstrating an impressive use of knots OVERHEAD. 3. How do they know how to do it?

    a. Most bird nests are so recognizable that an observer can

    determine its builder to species with no birds present.

    The nests are stereotyped, “if you’ve seen one Robin

    nest…..”

    b. Many birds raised in isolation in captivity can build nests

    nearly identical to those in the wild, suggesting a major

    innate component.

    c. Others clearly refine their nests based on experience.

    First year Eurasian Jackdaws start by shoving everything

    they can into a nest, but wind up selecting twig diameters

    and lengths that are very similar to those of adults.

    d. Some species imprint on the nest location and

    architecture in which they were raised -- especially

    raptors.

    D. Nest Safety. Predation on nests and their contents (eggs, chicks, and/or adults) can be very high, and it imposes a major constraint on avian fitness. Birds adopt nest building and attendance strategies that minimize predation risk via invisibility, inaccessibility, and impenetrability.

    1. Invisibility. Many nests are cryptic -- when adults sit on

    them they are nearly invisible. Ground nesting nightjars

    provide perhaps the best examples of this. Ground nesters,

    typically, are more at risk than tree nesters, since many

    mammalian predators are confined to terrestrial niches. In

    general, it is often hypothesized that predation rates are

    higher in tropics than elsewhere, but whether this is a result of high daily predation rates or longer development (and thus exposure) due to limited food is unclear.

    2. Inaccessibility.

    a. Building nests in trees helps, but there are also many

    arboreal predators -- squirrels, snakes, and especially

    other birds -- Jays, Crows, etc.

    b. Many birds build on islands safe from predators, where

    their numbers can reach astronomical heights. Horned

    Coots pile up stones in the middle of lakes on which they

    build reed nests -- they make their own islands.

    OVERHEAD

    3. Impregnability. Other birds build enclosed or pensile nests to discourage predators. Covered nests are less visible to predators sure, but often these nests cannot be penetrated by predators, which may be too large to squeeze through entrance holes. Also, pendulant nests effectively exclude snakes, which require supporting structures nearby to enter a nest.

    E. Colonial Nesting.

    1. Basics. About 13% of all birds nest colonially, including most seabirds. Evolution of colonial nesting behavior results from costs and benefits associated with (1) shortage of nesting sites that are safe from predators (2) abundant and/or unpredictable food that is distant from safe nest sites.

    2. Benefits. -- reduced predation.

    a. A safe spot for one pair is a safe spot for 1000 pair. b. A large group may be able to better detect and repel

    predators that a single pair.

    c. Predators may become satiated.

    3. Benefits -- increased foraging efficiency.

    a. Information Center Hypothesis -- example is Cliff

    swallows bringing food at higher rates too large than to

    small colonies. If food is patchy and unpredictable in its

    distribution, birds in a colony may be able to follow

    knowledgeable birds to feeding locations.

    b. Also, if food is patchy but superabundant and predictable,

    colonies may become established near them. These pops

    are probably not food limited -- example of Red Crossbill

    colonies near abundant areas of pine seeds, austral

    seabirds in path of Humboldt Current.

    4. Costs.

    a. Predation. Colonies may attract predators that would

    otherwise pass by highly dispersed nests -- Gulls often

    are attracted to other seabirds' nesting colonies. b. Intra-specific competition.

    i. Nest material stealing.

    ii. Could exhaust local food supplies.

    c. Could encourage build up of ectoparasites that would

    otherwise be held low. Cliff Swallows in large colonies

    had higher parasite loads than small colonies -- trade-off

    with 3a. Interesting to know growth rates of those chicks.

    F. Nest microclimates. [NOT COVERED not on exam]

    1. Eggs have very narrow temperature tolerances -- so nests are

    “designed” help maintain constant temperatures.

    2. Many nests thicknesses vary with local climate, as small

    deviations in thickness can greatly affect insulatory

    properties. A 5 mm difference n hummingbird nests can

    increase required energy inputs to maintain egg temps by

    13%.

    3. Deep burrows are very well insulated, but are poorly

    ventilated -- many burrow nesters' activities in nests is

    dictated more by CO build up than by temperature 2

    regulation.

    III. Incubation. [NOT COVERED not on exam]

    A. Brood Patches.

    1. To help keep eggs warm (optimal temp of most is 37-38;C),

    most birds develop a patch of featherless skin on their bellies.

    In some, the feathers drop involuntarily (hormone controlled),

    but in others (e.g., waterfowl) they pluck their own feathers,

    using the feathers in turn to line the nest.

    2. In sexes in which both sexes typically incubate, both sexes

    develop the patch. In many others, only the females develop

    a brood patch, which can be useful in sexing birds in the hand

    during the breeding season. However, usually both sexes are

    capable of developing a brood patch, in case one sex dies

    before fledging, the other can take over.

    B. Thermoregulation.

    1. Keeping eggs warm.

    a. The safe range is 35-41. Below 35 and development in

    greatly slowed, below 26 and the embryo rarely recovers.

    b. Most birds regulate temperature by alternating sessions of

    incubation and recesses. OVERHEADS

    c. Experiments altering nest temperature have resulted in

    predicted changes of session/recess behaviors.

    d. They continually rotate and turn eggs to keep them all

    approximately the same temperature.

    e. Other strange adaptations do exist -- moundbuilders

    regulate temperature of eggs resting on top of rotting

    vegetation.

    2. Keeping eggs cool.

    a. Birds nesting open sunny environments (tropical seabirds)

    risk dangerously high egg temperatures.

    b. They often sit to minimize heat gain; their black backs

    absorbing heat and the wind whisking it away.

    c. Many also periodically cover the eggs lightly with water

    to increase evaporative cooling, or they sprinkle with

    sand to provide insulation from the heat.

    C. Incubation Periods.

    1. Incubation periods range from 10-100 days. Defined as date

    of last egg laid to last hatch date.

    2. Corresponds, quite roughly, to body size. Small song birds

    have the shortest incubation periods. Much variation

    however.

    3. Woodpeckers have very short incubation periods for their

    body size. Their young are especially altricial -- perhaps an

    adaptation to minimize time until chicks can thermoregulate

    (chicks better than eggs at thermoregulation) to enable adults

    to spend time off nest procuring food for them. Probably

    only possible because woodpeckers nests are so safe from

    predators by being in new cavities.

    4. Species with precocial young typically have longer

    incubation periods.

    5. To some extent, there is a trade-off between adult and young

    survival in incubation periods. The longer the chicks remain

    quiet in eggs, the more likely they will survive. But, the

    longer an adults sits vulnerably on the nest, the more likely

    she/he is to be nailed by a predator. So you might expect

    species with long lives to maximize lifetime reproductive

    success (LRS) by opting for proportionately shorter

    incubation periods. Problem with testing this idea is that

    longer-lived species also tend to be larger bodied, which

    elevates incubation period. It is not clear what determines

    inter and intra-specific differences in incubation periods.

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