V formation is used in mostly larger birds during migration. These birds use the tip vortices of the birds in front of them to gain more lift, but it is tricky. They have to be in a place where the hit the right part of the footprint left by the bird in front of them which is not easy, since the footprint will move up and down and in an out in relation to where the flapping wing is at the time. The phasing in flapping between the birds and their location has to be just right to make it work. There is a paper that will tell you all about it.
Is there a difference in the foot prints at different speeds?
Yes, the footprint changes with flight speed. Check it out for Tadarida brasiliensis.
What about the effect of elevation?
Altitude, temperature and humidity all affect air density. If you calculate lift it goes as follows: Lift=0.5*air density*wing area*speed^2*lift coefficient. Use http://www.denysschen.com/catalogue/density.aspx if you want to check out how much of an effect it has and don’t forget to switch to metric.
What about efficiency at different speeds?
Tough one. My guess would be they fly more efficiently at higher speeds, but nobody has measured it.
If lifestyle affects or evolves in tandem with flight footprint (for example, food foraging and migration habits), could roost choice also be related to flight capability (like wing design)?
There are definitely big differences in landing performance depending on roost choice. Check out these videos of cave and tree roosting bats
Questions remain about landing, how does the flight footprint change?
Nobody knows yet.
What are the real world application for this? Airplane model design perhaps
Google bioinspired Micro air vehicles
What species were studied. What about gliding birds and flying squirrels compared to the footprint of bats?
I myself studied 3 species in the wind tunnel
Tadarida brasiliensis (Mexican freetail bat)
Myotis velifer (cave myotis)
Cynopterus brachyotis (dog faced fruit bat)
Other groups have studied the Pallas’s long-tongued bat (Glossophaga soricina) and the lesser long-nosed bat (Leptonycteris yerbabuenae). There are also data for some bird species: the pied flycatchers (Ficedula hypoleuca), the blackcap (Sylvia atricapilla) and the swift
How long, why so long to study three species?
Much of the time went into designing the experiment and setting up the equipment. Particle image velocimetry had just started to become available and synchronizing laser measurements with kinematic measurements took a lot of effort. Training the bats to fly in the wind tunnel was also not easy. If you look at articles about birds and bats in wind tunnels you will find that the sample size is very low. Not good, but sometimes that is all you can do.
Does the flight footprint change when the bat is pregnant or after feeding?
There has been no research into how pregnancy influences flight performance, so all we can do is speculate. The bat will be much heavier so it would need to generate more lift. How high lift is depends on the density of the medium (air and it does not change), speed, wing area and wing shape and angle (lift coefficient). The bat might be able to increase the wing area during times of the wing beat cycle when the wings were not completely extended as well as changing the shape by changing the wing motion. Speed is important to generate lift. The faster the more lift. Trouble starts when one flies slowly. So I would say that pregnant bats probably have trouble to fly slow and need to work harder.
Are there individual differences within species? Would you attribute them to age, gender, genetics?
Good question. There are individual differences, but due to the low sample size we have not yet be able to relate them to age or gender. Check out the wing path trajectories for four dog faced fruit bats.
Is it true bats have to drop off something to get started? What about after a crash? What does the flight footprint look like from a bat leaving the ground after a crash vs attaining flight by dropping off the ceiling?
Nobody knows how the footprints look like. We have only studied them for straight flight. Bats can definitely take off from the ground. Here is an article about the topic.
“MacAyeal, Leigh C., et al. “Climbing flight performance and load carrying in lesser dog-faced fruit bats (Cynopterus brachyotis).” The Journal of experimental biology 214.5 (2011): 786-793.”
Some bat species do it all the time. The vampire bat can walk and run and approaches its prey from the ground and at the end has to start from there