The high metabolic rates of birds during the active part of the day is supplemented by rest at other times. Sleeping birds often use a type of sleep known as vigilant sleep, where periods of rest are interspersed with quick eye-opening "peeks", allowing them to be sensitive to disturbances and enable rapid escape from threats. Swifts are believed to be able to sleep in flight and radar observations suggest that they orient themselves to face the wind in their roosting flight. It has been suggested that there may be certain kinds of sleep which are possible even when in flight. Some birds have also demonstrated the capacity to fall into slow-wave sleep one hemisphere of the brain at a time. The birds tend to exercise this ability depending upon its position relative to the outside of the flock. This may allow the eye opposite the sleeping hemisphere to remain vigilant for predators by viewing the outer margins of the flock. This adaptation is also known from marine mammals. Communal roosting is common because it lowers the loss of body heat and decreases the risks associated with predators. Roosting sites are often chosen with regard to thermoregulation and safety.
If it is possible to answer this question, answer it for me (else, reply "unanswerable"): Why is communal roosting common?
Ah, so.. because it lowers the loss of body heat

Usually a Presbyterian church will not have statues of saints, nor the ornate altar more typical of a Roman Catholic church. Instead, one will find a "communion table," usually on the same level as the congregation. There may be a rail between the communion table and the "Chancel" behind it, which may contain a more decorative altar-type table, choir loft, or choir stalls, lectern and clergy area. The altar is called the communion table and the altar area is called the Chancel by Presbyterians. In a Presbyterian (Reformed Church) there may be an altar cross, either on the communion table or on a table in the chancel. By using the "empty" cross, or cross of the resurrection, Presbyterians emphasize the resurrection and that Christ is not continually dying, but died once and is alive for all eternity. Some Presbyterian church buildings are often decorated with a cross that has a circle around the center, or Celtic cross. This not only emphasized the resurrection, but also acknowledges historical aspects of Presbyterianism. A baptismal font will be located either at the entrance or near the chancel area. Presbyterian architecture generally makes significant use of symbolism. You may also find decorative and ornate stained glass windows depicting scenes from the bible. Some Presbyterian churches will also have ornate statues of Christ or Graven Scenes from the Last Supper located behind the Chancel. St. Giles Cathedral ( Church Of Scotland- The Mother Church of Presbyterians) does have a Crucifix next to one of the Pulpits that hangs alongside. The image of Christ is more of faint image and more modern design.
If it is possible to answer this question, answer it for me (else, reply "unanswerable"): What is located on a different level than the congregation in a Presbyterian church?
Ah, so.. unanswerable

Philosophy has become an increasingly academic discipline. More of its practitioners lament this situation than occurs with the sciences; nonetheless most new philosophical work appears in academic journals. Major philosophers through history—Plato, Aristotle, Socrates, Augustine, Descartes, Kierkegaard, Nietzsche—have become as canonical as any writers. Some recent philosophy works are argued to merit the title "literature", but much of it does not, and some areas, such as logic, have become extremely technical to a degree similar to that of mathematics.
If it is possible to answer this question, answer it for me (else, reply "unanswerable"): Most serious studies in philosophy are segregated to what publications?
Ah, so..
academic journals