ORNITHISCHIANS

ORNITHISCHIAN BEHAVIOR

~after Bird Behavior by Donald & Lillian Stokes

 

 

Tyrannosaurus  Rex:  

AUDITORY DISPLAYS

Song

A rapid, rising bubbly song with a bounce.  Distinguished by a “Bibble-bibble” at the end of each sequence.

Males only

CONTEXT  On territory at beginning of breeding season

  Calls

Twigger-Call

“TWIG’GER-TWIG’ER-TWIG’GER-TWIG’GER

Male or female

A low buzzy call with a strong accent on the first syllable.  May be repeated up to five times, growing louder and higher each time.

CONTEXT  On territory at beginning of breeding season by male;  by either male or female when nest is approached.   Occasionally while hunting, when prey is scarce.

 

Peel-Call

“PEEEL, PEEEL,  PEEEEL”

Male or female

Soft, high-pitched, each syllable distinct.

CONTEXT  During courting behavior, between parents and young during feeding.

 

Bibble-bibble-Call

“BIBBLE, BIBBLE”

Male or Female

Bubbly, rapid, rising and falling in pitch.  May be repeated many times.

CONTEXT  Between male and female during mating, also during nest-building and between members of a flock while hunting.

VISUAL DISPLAYS

See-sawing

Male

Front feet are held out to the sides to aid balance while the dinosaur alternately raises and lowers his tail and head in see-saw fashion and shuffles his feet to turn slowly in a circle.  Usually occurs on rise of ground.

CALLS  Twigger-call or Song

CONTEXT  On territory at beginning of breeding season, and for a few days after arrival of females.

Display Fighting

Males

Two males bang the tops of their heads together while gnashing their teeth and scrabbling at one another with front feet.  Very rarely results in injury.

CALLS  None.

CONTEXT  On territory, after one male has challenged another.

Horizontal Fluff

Male or Female

Stretched in a horizontal posture, the dinosaur fluffs its head feathers.  The mouth is open.

CALL  Twigger-call

CONTEXT  Given when another T. Rex approaches nesting area.  Occasionally directed at other dinosaur species as well.

Side Hop

Male or Female

Dinosaur with food in its mouth hops sideways toward another and passes the food.

CALL  Peel-call or Bibble-bibble-call

CONTEXT  A courtship behavior initiated by the female.  If the male accepts the food, she waits while he finds and brings a piece of food to her.  If he does not accept it, she may try again, but will generally leave his territory and approach another male.   Also occasionally between a mother and a fledgling.  Observed on rare occasions between two females.

Necking

Male and Female

A mated pair rub heads and entwine necks while clicking teeth

CALL  Bibble-bibble-call

CONTEXT  Before and after copulation

Begging

Male or Female Young

Arms are held at sides and fluttered up and down while the dinosaur leans forward with its mouth open wide

CALL  Peel–call

CONTEXT  Given by nestlings and fledglings when they receive food from parents.

 

BEHAVIOR

Territory

Size:  2-4 Square Miles

Main Behaviors:  See-sawing, Twigger-Call, Song

The size of a T. Rex pair’s territory depends upon the availability and variety of food sources.  The male begins to claim a territory late in the dry season by standing on a hill or ridge of ground near the center of the desired area and See-sawing, while giving Song.  Usually there is little competition, but occasionally another male will approach the See-sawing male while its back is turned and begin See-sawing without Song.  When the intruder’s presence is recognized by the first dinosaur, a Display Fight generally ensues.  The vanquished dinosaur will back away from the victor, who immediately continues See-sawing and increasingly loud Song.  Females within the area watch these behaviors closely and initiate courtship immediately after Territory is established.

Mating

Main Behaviors:  Side Hopping, Necking, Peel–Call, Bibble-bibble-Call

Once the male has established a Territory, an interested female will approach Side Hopping.  If the male reciprocates, Necking and copulation follow very quickly, and continue for several hours.  Females may travel great distances before they find Territories that are satisfactory and males that will accept them.  This appears to be the case especially when food is scarce, perhaps acting as a control on population.

Nesting

Main Behaviors: Horizontal Fluff, Twigger-call

The nest is built by the female alone, while the male watches to keep intruders away with the Horizontal Fluff display.  The female scratches a rudimentary hole in the dust, and lines it with grass stems and dead fronds.  Between five and twelve pale blue oval eggs are laid at the rate of one or two a day, and brooding begins after all eggs have been laid.  The male shares brooding, and the non-brooding T. Rex will generally leave the area to hunt.  Because eggs are one of the favored foods of carnivorous dinosaurs, nests are guarded closely.  Observers have not seen a T.Rex consume eggs of its own species if the nest is guarded, but an unguarded nest, though very rare, is considered fair game.

Nestlings and Fledglings

Main Behaviors:  Side Hop, Begging, Horizontal Fluff, Peel-Call, Twigger-Call

Eggs hatch within a few hours of one another, usually during a two-day period.  Nestlings are covered with fine dull gray feathers, which fluff out within a few hours.  The nestlings are  brooded by the female only, while the male hunts.  He feeds the female first, bringing her large pieces of meat, then regurgitates a semi-digested “Tyrannosaurus Milk” to the young.  Commonly only three or four young survive this stage, since competition for food is vigorous.   After six or seven days, the young begin to leave the nest for short periods, but never stray far.  The male then takes his turn guarding the young, freeing the female to hunt on her own.  Both parents Feed.  When the young are hopping about strongly–in about ten days–the parents lead them away from the nest, in single file, with the female (usually) in the lead and the male bringing up the rear.  Along the way, both parents hunt small game and bring it live to the young ones who attempt complete the kill.  After another week, the young generally hunt well enough on their own to venture short distances away from the parents, but the parents are still watchful, and remain so until the young are nearly full grown.  During the entire period, the young are protected from predators by the parents, first by warning calls, then by direct attack, if necessary.  However, once the young are half-grown, the only serious threats to them are environmental.

Group Behavior

Main Behaviors: Bibble-bibble-Call, Display Fighting (among males), Twigger-Call

After the nesting season is over, the T. Rex family groups stay together until mating season begins again.  They hunt, sometimes cooperatively.  When food is abundant, there is no competition between family groups, but in times of scarcity, both sexes may give the Twigger-Call, and males may engage in Display Fighting. Just before sunset, they settle on a rise in the land, often an old nest site, and the young run around for an hour or so until nearly dark, at which time the family group huddles together for warmth.

Near the beginning of the following dry season,  the juveniles lose all but their head feathers and leave their parents.  Each group of siblings will stay together for another year.  They may form larger flocks with one or two other juvenile groups.  When they reach sexual maturity at the age of three, these flocks disperse and the young dinosaurs go off alone to find their own Territories and mates.

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