Shorebirds Terms

Thecodont hypothesis

Birds are not dinosaurs but are descendents from reptiles and are closely related to crocodiles. Feathers evolved for flight then for thermoregulation. Flight evolved from arboreal animals most likely from gliding behaviors. 

This hypothesis is likely correct because there is preserved skeletal evidence. The bone morphology of discovered individuals have shown similar forelimb and hindlimb adaptations that are found in modern day birds. There is also fossil evidence of theropod dinosaurs with feathers. The fossil evidence shows that these theropods with feathers would be too heavy to fly. This supports the hypothesis of feathers being evolved for thermoregulation. 

Theropod hypothesis

Birds are dinosaurs; they are descendents from small cursorial dinosaurs. They developed feathers for thermoregulation before flight. Most likely developed flight by running and jumping.

Migration

 Predictable round trip movement 

Partial migration

When a segment of the population migrates while the rest stay back

Phylogenetic Species Concept

This concept defines a species as a group with shared derived characteristics between members of a population from their lineage of ancestors. A strength would be that it includes all species even hybridization and it focuses on evolved characteristics

Biological Species Concept

This concept defines a species as a group that can interbreed and produce offspring but are reproductively isolated from others. Its strength is that it is good for understanding changes in populations that are reproductively isolated. Its weakness is that it excludes hybridization between species. This would reduce the overall number of bird species to a couple thousand or fewer. A lot of species would be lost then

Determinate (layer)

birds that lay a fixed number of eggs per clutch

Indeterminate (layer)

birds that don’t have a fixed number of eggs per clutch and can adjust clutch size in response to external factors

Altricial Young

Offspring hatch without feathers and their eyes are closed

Precocial Young

Offspring hatch with feathers and open eyes. They are able to walk around and leave the nest. (they are “Pre-made”)

-require more energy to produce, take longer to hatch

Lack’s hypothesis

Females try to maximize the number of fledglings per clutch. It also suggests that the survival rate of fledglings decreases as clutch sizes increase. This applies to indeterminate layers because their decision to lay any amount of eggs is driven by the resources available once the eggs hatch. 

Female birds lay clutches smaller than predicted because adults experience a lower survival rate with larger clutches due to increase of energy input and reduction of resources for themselves. 

Polyandry

one female and multiple males

-rarest mating system

Monogamy

One male and one female

Polygyny

One male, multiple females

Promiscuity

Multiple mating partners without pair bonds

Courtship scrape

shallow depression made in the sand during courtship to serve as a potential nest site

Concealed Nesters

Birds that rely on areas thick with vegetation to hide their eggs

-lay large clutches

Open Nesters

Birds that rely on open spaces that are able to camouflage their eggs

-plovers, willets, oystercatchers

-lay small clutches

Brooding

Bird sits on eggs to incubate or to keep hatchlings warm

Resource Defense Monogamy

Male defends a territory with resources to attract a mate

-shared parental care varies

-Dunlin, killdeer, long-billed curlew

Resource Defense Polygyny

Male defends a territory that can sustain multiple mates

Male Dominance Polygyny

Males compete by lekking

-No resources

-Large males w/ colors

-females do parental care

-seen in ruffs

Mate Access Polyandry

Females compete for and defend males

- No resources

-Females are larger w/ color

-males provide all parental care

-Phalaropes

Prokinesis

Flexion of the the upper beak in relation to the cranium

-Upwards past resting point (protration)

-Downwards past resting point (retraction)

Rhynchokinesis

Flexion of the tip of the upper bill in relation to the cranium

-Region of thinner bone called “hinges” at the base of the beak

Herbst corpuscles

Pressure and vibration sensitive receptor on the beaks of birds

Uropygial gland

“preen gland” or “Oil gland” located above the tail and is used to rub oil over feathers for waterproof or cleaning purposes

Prebasic molt

A bird sheds its feathers and becomes flightless for a period of time.

-can be an adaptation to wintering on predator free regions

Prealternate molt

Partial feather replacement birds undergo prior to the breeding season

-replaces dull colored feathers

Seasonal Atrophy

Shrinkage of a bird’s organs at a certain point of the year

Wing loading

The ratio of a bird’s mass to its total wing surface

Resource defense polyandry

Females defend territories with resources to host multiple mates

-males provide most parental care

Quasi parasitism

Female lays an egg in another female's nest, and that egg is fertilized by the male partner

-host male fertilizes the outsider's egg

-rare

Brood parasitism

Female lays eggs in the nest of another to make the other bird raise its young

Philopatry

Tendency of an organism to stay or return to its natal site

Intraspecific variation

differences in traits, behaviors, etc. among individuals of the same species

Nidicolous

Offspring stays at their nest

-usually blind, featherless, rely on parents

Nidifugous

Offspring leave nest shortly after hatching

-have feathers, open eyes, don’t rely on parents as much

-Shorebirds are this

Interspecific variation

The differences in traits or characteristics between different species

-comparisons of species by anatomy, biology, or physiology

-eg. Long-billed curlew vs swainson’s thrush

Migration

The predictable seasonal movement of individuals between breeding grounds and wintering areas.

-tendency for this is caused by natural selection

Stopover

A temporary resting period where a bird takes a break in their migration

Staging Site

A location where shorebirds can stop during migration to rest and feed to regain energy before crossing major geographical barriers

Partial Migrant

Species or populations consisting of a mix of individuals w/ varying migratory tendencies

-some undergo short movements

-others end up staying back year round permanently

-eg. snow plovers

What forms of fuel power a shorebird’s migration?

Carbohydrates, lipids, and proteins

Hypertrophy

increase of organ mass and size

-usually seasonall

-enlarges skeletal flight muscles in some

-preparation for migration

Atrophy

Shrinkage of organ mass and size overtime

-occurs during migration

-reduces need to stop during migration route

-reduces a bird’s wingload

Loop migration

Birds take a route to get to their breeding grounds but will take a different route when returning to their non breeding grounds

Hop migration

Shorebirds migrate short distances to multiple staging sites throughout their entire migration route

-eg. dunlin

Skip migration

Shorebirds migrate moderate distances to a few staging sites for their entire migration route

Jump migration

Shorebirds migrate long distances with very few staging sites throughout their entire migration route

-experience hypertrophy of flight muscle

-experience atrophy of their digestive system

-eg. Bar-tailed godwits

Leapfrog migration

Seasonal movement where populations of the same species that breed farther north pass over the southern breeding populations and spend winters farther down south

-Reversed latitudinal order

-Northern Breeders winter south of southern breeders

What do shorebirds need to manage during migration?

-Time

-Energy

-Danger risks

Flyaways

Established migratory routes used seasonally by shorebirds

How many flyaways are recognized worldwide?

nine are recognized worldwide

-Pacific Americas

-Central Americas

-Atlantic Americas

-East Atlantic

-Black Sea Mediterranean

-West Asian, East African