strain on the muscles during soaring flight. Even within a species wing morphology may differ. For example, adult European Turtle Doves have been found to have longer but more rounded wings than juveniles – suggesting that juvenile wing morphology facilitates their first migrations, while selection for flight maneuverability is more important after the juveniles' first molt. Female birds exposed to predators during ovulation produce chicks that grow their wings faster than chicks produced by predator-free females. Their wings are also longer. Both adaptations may make them better at avoiding avian predators. Wing shape The shape of the wing is important in determining the flight capabilities of a bird. Different shapes correspond to different trade-offs between advantages such as speed, low energy use, and maneuverability. Two important parameters are the aspect ratio and wing loading. Aspect ratio is the ratio of wingspan to the mean of its chord (or the square of the wingspan divided by wing area). A high aspect ratio results in long narrow wings that are useful for endurance flight because they generate more lift. Wing loading is the ratio of weight to wing area. Most kinds of bird wing can be grouped into four types, with some falling between two of these types. These types of wings are elliptical wings, high speed wings, high aspect ratio wings and slotted high-lift wings. Elliptical wings Technically, elliptical wings are those having elliptical (that is quarter ellipses) meeting conformally at the tips. The early model Supermarine Spitfire is an example. Some birds have vaguely elliptical wings, including the albatross wing of high aspect ratio. Although the term is convenient, it might be more precise to refer to curving taper with fairly small radius at the tips. Many small birds have a low aspect ratio with elliptical character (when spread), allowing for tight maneuvering in confined spaces such as might be found in dense vegetation. As such they are common in forest raptors (such as Accipiter hawks), and many passerines, particularly non-migratory ones (migratory species have longer wings). They are also common in species that use a rapid take off to evade predators, such as pheasants and partridges. High speed wings High speed wings are short, pointed wings that when combined with a heavy wing loading and rapid wingbeats provide an energetically expensive high speed. This type of flight is used by the bird with the fastest wing speed, the peregrine