question: If a bird would fly in a stationary bus, when the bus would accelerate, would the bird go backwards? (Similar how we get “pulled” backwards upon acceleration?)
comment: Yes, a bird is going to be subject to the same inertial forces as human passengers in a vehicle. The difference though is that the bird is pushing against the air while the people are interacting with the seats. Air within the vehicle tends to move with the vehicle so a bird will experience a sort of "wind" moving with the car, so a bird hovering in a car going 60 mph is going to effectively be hovering at rest with respect to a 60 mph wind, feeling no pull in any direction other than that of gravity. As the vehicle stops the bird will want to keep moving as it was before and as it moves through the car experience an opposing wind. With insects this wind is often enough to halt their movement in short order, but a more massive bird might experience difficulty avoiding the front of the vehicle.
passages: Section::::Origin of flight hypothesis.:Response.
  
  One possible problem with the WAIR origin of flight hypothesis was noticed by Philip Senter. He argued that early birds, including "Archaeopteryx", lacked the shoulder mechanism by which modern birds' wings produce swift, powerful upstrokes. Since the downforce on which WAIR depends is generated by upstrokes, Senter argued that early birds were incapable of WAIR or flapping flight.
   When an efferent signal is produced and sent to the motor system, it has been suggested that a copy of the signal, known as an efference copy, is created so that exafference (sensory signals generated from external stimuli in the environment) can be distinguished from reafference (sensory signals resulting from an animal's own actions).
   Unlike most air vehicles, in which the objects that generate lift (wings) and thrust (engine/propeller) are separate and the wings remain fixed, flying animals use their wings to generate both lift and thrust by moving them relative to the body. This has made the flight of organisms considerably harder to understand than that of vehicles, as it involves varying speeds, angles, orientations, areas, and flow patterns over the wings.
   Two studies of rufous or Anna's hummingbirds in a wind tunnel used particle image velocimetry techniques to investigate the lift generated on the bird's upstroke and downstroke. The birds produced 75% of their weight support during the downstroke and 25% during the upstroke, with the wings making a "figure 8" motion.
   BULLET::::- "Wing-assisted incline running" (WAIR), a version of "from the ground up" in which birds' wings originated from forelimb modifications that provided "downforce", enabling the proto-birds to run up extremely steep slopes such as the trunks of trees.
  
  BULLET::::- "Pouncing proavis", which posits that flight evolved by modification from arboreal ambush tactics.
   In March 2018, scientists reported that "Archaeopteryx" was likely capable of flight, but in a manner substantially different from that of modern birds.
  
  Section::::Origin of bird flight.:Cursorial ("from the ground up") theory.
  
  The cursorial theory of the origin of flight was first proposed by Samuel Wendell Williston, and elaborated upon by Baron Nopcsa. This hypothesis proposes that some fast-running animals with long tails used their arms to keep their balance while running. Modern versions of this theory differ in many details from the Williston-Nopcsa version, mainly as a result of discoveries since Nopcsa's time.
   A bird or bat flying through the air at a constant speed moves its wings up and down (usually with some fore-aft movement as well). Because the animal is in motion, there is some airflow relative to its body which, combined with the velocity of its wings, generates a faster airflow moving over the wing. This will generate lift force vector pointing forwards and upwards, and a drag force vector pointing rearwards and upwards. The upwards components of these counteract gravity, keeping the body in the air, while the forward component provides thrust to counteract both the drag from the wing and from the body as a whole. Pterosaur flight likely worked in a similar manner, though no living pterosaurs remain for study.
   The fundamentals of bird flight are similar to those of aircraft, in which the aerodynamic forces sustaining flight are lift and drag. Lift force is produced by the action of air flow on the wing, which is an airfoil. The airfoil is shaped such that the air provides a net upward force on the wing, while the movement of air is directed downward. Additional net lift may come from airflow around the bird's body in some species, especially during intermittent flight while the wings are folded or semi-folded (cf. lifting body).
   Lift is produced by the changing direction of the flow around a wing. The change of direction results in a change of velocity (even if there is no speed change, just as seen in uniform circular motion), which is an acceleration. To change the direction of the flow therefore requires that a force be applied to the fluid; lift is simply the reaction force of the fluid acting on the wing.
   BULLET::::- In Disney's The Hunchback of Notre Dame (1996 film), Laverne is seen shouting to a flock of pigeons flying to the guards, "Fly my pretties, fly!" with background music that strongly resembles the music in the 1939 "Wizard of Oz" scene when the Wicked Witch sends out the flying monkey bats to capture Dorothy.
   BULLET::::- Slowest. Most flying animals need to travel forward to stay aloft. However, some creatures can stay in the same spot, known as hovering, either by rapidly flapping the wings, as do hummingbirds, hoverflies, dragonflies, and some others, or carefully using thermals, as do some birds of prey. The slowest flying non-hovering bird recorded is the American woodcock, at .
   Steady flight is defined as flight where the aircraft's linear and angular velocity vectors are constant in a body-fixed reference frame such as the body frame or wind frame. In the Earth frame, the velocity may not be constant since the airplane may be turning, in which case the airplane has a centripetal acceleration ("V"cos("γ"))/"R" in the "x"-"y" plane, where "V" is the magnitude of the true airspeed and "R" is the turn radius.
   Figure 1 (top) shows an accelerating car. When a car accelerates, a passenger feels like they're being pushed back into the seat. In an inertial frame of reference attached to the road, there is no physical force moving the rider backward. However, in the rider's non-inertial reference frame attached to the accelerating car, there "is" a backward fictitious force. We mention two possible reasons for the force to clarify its (the force's) existence:
   The term "Proavis" was used again in 1999, when Joseph Garner, Graham Taylor, and Adrian Thomas proposed their "pouncing proavis model", an hypothesis entailing that the origin of avian flight rested in a predatory behaviour, the "proavis" jumping on its prey from trees (see "pouncing proavis model" in Origin of avian flight).
   A cursorial, or "running" model was originally proposed by Samuel Wendell Williston in 1879. This theory states that "flight evolved in running bipeds through a series of short jumps". As the length of the jumps extended, the wings were used not only for thrust but also for stability, and eventually eliminated the gliding intermediate. This theory was modified in the 1970s by John Ostrom to describe the use of wings as an insect-foraging mechanism which then evolved into a wing stroke. Research was conducted by comparing the amount of energy expended by each hunting method with the amount of food gathered. The potential hunting volume doubles by running and jumping. To gather the same volume of food, "Archaeopteryx" would expend less energy by running and jumping than by running alone. Therefore, the cost/benefit ratio would be more favorable for this model. Due to "Archaeopteryx's" long and erect leg, supporters of this model say the species was a terrestrial bird. This characteristic allows for more strength and stability in the hindlimbs. Thrust produced by the wings coupled with propulsion in the legs generates the minimum velocity required to achieve flight. This wing motion is thought to have evolved from asymmetrical propulsion flapping motion. Thus, through these mechanisms, "Archaeopteryx" was able to achieve flight from the ground up.
   Avian species also display unique escape responses. The escape response of birds may be particularly important when considering aircraft and vehicle traffic. In one experiment by Devault et al. (1989), brown-headed cowbirds ("Molothrus ater)" were exposed to a demonstration of traffic travelling at speeds between 60 – 360 km/hr. When approached by a vehicle travelling at 120 km/h, the birds only allotted 0.8s to escape before a possible collision. This study showed that fast traffic speeds may not allow enough time for birds to initiate an escape response.
  
  Section::::Examples.:Escape response in fish.
   Various theories exist about how bird flight evolved, including flight from falling or gliding (the "trees down" hypothesis), from running or leaping (the "ground up" hypothesis), from "wing-assisted incline running" or from " proavis" (pouncing) behavior.
  
  Section::::Basic mechanics of bird flight.
  
  Section::::Basic mechanics of bird flight.:Lift and drag.
   Section::::Evolution of bird flight.:Pouncing proavis model.
  
  The proavis theory was first proposed by Garner, Taylor, and Thomas in 1999:
  
  We propose that birds evolved from predators that specialized in ambush from elevated sites, using their raptorial hindlimbs in a leaping attack. Drag–based, and later lift-based, mechanisms evolved under selection for improved control of body position and locomotion during the aerial part of the attack. Selection for enhanced lift-based control led to improved lift coefficients, incidentally turning a pounce into a swoop as lift production increased. Selection for greater swooping range would finally lead to the origin of true flight.
   Most paleontologists agree that birds evolved from small theropod dinosaurs, but the origin of bird flight is one of the oldest and most hotly contested debates in paleontology. The four main hypotheses are:
  
  BULLET::::- "From the trees down", that birds' ancestors first glided down from trees and then acquired other modifications that enabled true powered flight.
  
  BULLET::::- "From the ground up", that birds' ancestors were small, fast predatory dinosaurs in which feathers developed for other reasons and then evolved further to provide first lift and then true powered flight.
   Leonardo starts off folio 5 by stating that if a man were to be in a flying machine, nothing should get in his way from the waist up, so that he can balance himself as one does in a boat. He goes on to write on how a bird's direction will change with the direction of the wind. A bird which is going in a straight line that comes into a cross breeze at a perpendicular angle will now be heading in a direction that is in between the two endpoints of each direction. He ends the first page by explaining that if a bird in a descent wants to turn left or right, then it will lower the wing on the side of the direction it wants to turn.
   BULLET::::- Dodger, an elderly cat in Dorset, England, took round trips on several buses and is suspected to be motivated by the warmth.
  
  However, dogs and cats have also been observed to ride public transport before disembarking at a destination:
  
  BULLET::::- Eclipse, a black labrador in Seattle, would occasionally ride the bus ahead of its owner when eager to get to the dog park.
  
  BULLET::::- Ratty, a Jack Russell terrier in Yorkshire, England, traveled five miles by bus to be fed at two pubs.
   In 2010, Robert L. Nudds and Gareth J. Dyke in the journal "Science" published a paper in which they analysed the rachises of the primary feathers of "Confuciusornis" and "Archaeopteryx". The analysis suggested that the rachises on these two genera were thinner and weaker than those of modern birds relative to body mass. The authors determined that "Archaeopteryx" and "Confuciusornis", were unable to use flapping flight. This study was criticized by Philip J. Currie and Luis Chiappe. Chiappe suggested that it is difficult to measure the rachises of fossilized feathers, and Currie speculated that "Archaeopteryx" and "Confuciusornis" must have been able to fly to some degree, as their fossils are preserved in what is believed to have been marine or lake sediments, suggesting that they must have been able to fly over deep water. Gregory Paul also disagreed with the study, arguing in a 2010 response that Nudds and Dyke had overestimated the masses of these early birds, and that more accurate mass estimates allowed powered flight even with relatively narrow rachises. Nudds and Dyke had assumed a mass of for the Munich specimen "Archaeopteryx", a young juvenile, based on published mass estimates of larger specimens. Paul argued that a more reasonable body mass estimate for the Munich specimen is about . Paul also criticized the measurements of the rachises themselves, noting that the feathers in the Munich specimen are poorly preserved. Nudds and Dyke reported a diameter of for the longest primary feather, which Paul could not confirm using photographs. Paul measured some of the inner primary feathers, finding rachises across. Despite these criticisms, Nudds and Dyke stood by their original conclusions. They claimed that Paul's statement, that an adult "Archaeopteryx" would have been a better flyer than the juvenile Munich specimen, was dubious. This, they reasoned, would require an even thicker rachis, evidence for which has not yet been presented. Another possibility is that they had not achieved true flight, but instead used their wings as aids for extra lift while running over water after the fashion of the basilisk lizard, which could explain their presence in lake and marine deposits (see Evolution of bird flight).
   The thrust to propel the aircraft forward comes from its propellers or jet engines. Reverse thrust for backing up can be generated by thrust reversers such as on the Boeing C-17 Globemaster III, or reversible pitch propellers such as on the Lockheed C-130 Hercules. Most aircraft, however, are not designed to back up on their own and must be pushed back either by hand or by using an aircraft tug.
   Section::::Description.
   Section::::Evolution of bird flight.:Wing-assisted incline running.
  