Navigation by the sky

One of the most common methods of avian navigation is to use both the sun and stars for orientation, using them for navigation. In the opinion of Keeton (1979), avian navigation by celestial objects is the most commonly used method of navigation amongst most bird species.

Navigation by the Sun

In a study conducted, Matthews (1952) discovered that homing pigeons are capable of "bico-ordinate navigation" only while the sun is up. As soon as cloud cover was introduced the pigeons lost all sense of direction, demonstrating clearly their reliance on the sun to navigate.

But how do birds navigate using the sun? In a study conducted in 1953, Kramer demonstrated that pigeons in a circular cage will use the sun to obtain compass directions and will then use those directions to navigate. This idea was further elaborated upon by Schmidt-Koenig (1960), who further declared that pigeons were using the position of the sun in conjunction with their internal body clocks to use the sun as a compass and navigate from it.

This diagram from Keeton (1979), shows the orientation of pigeons flight directions. This experiment involved altering the body clocks of the pigeons by six hours. The dashed line shows the direction of "home" with the dots around the perimeter showing where the pigeons vanished from sight. This shows that the pigeons knew where "home" was in relation to the position of the sun and their own body clocks, which they then used to determine the direction they needed to go.

Ultimately, navigating by the sun is one way that many birds navigate around the world. However, what happens when the sun goes down and can no longer be used for navigation. Especially in the case of nocturnal predators and birds that undertake very long migrations, how do they navigate at night?

Navigation by the stars

The first demonstration that birds could navigate using the stars was conducted in 1957 by Sauer, who demonstrated that European warblers could navigate using the stars. Since then more experiments followed, most notably the demonstration conducted by Emlen (1975), who conclusively proved that indigo buntings were navigating by the stars by putting the birds in a similar environment to those used to test pigeons in daylight. Unlike the pigeons however, the buntings derived the direction almost immediately whereas the pigeons had to circle for a while before orientating themselves. This is because using the stars as a compass does not require a bird to also use it's body clock in order to work out it's direction of travel. By using the star Polaris, the birds are able to instantly work out their orientation and can then navigate accordingly. 

Similarly to the work with pigeons, Emlen (1975), also demonstrated the nocturnal equivalent of altering the pigeons body clocks, by instead putting buntings that had been living in a spring environment into an autumn constellation to see if they would still fly in the expected direction. 

The above diagram from the experiment shows that the buntings still flew along the bearing that they were supposed to even though they were now in a different celestial zone.

Navigating by using the sky is one of the most common methods of navigation used by birds, but it is also a method fraught with danger. How do the birds navigate if there is too much cloud cover, either during the day or night?