clump of moss or grass. Males defend the breeding territory by gliding and fluttering above it while making oinking and rattling sounds. When on the ground, the male stretches its wing out to the side and raises its tail into the air to display the white patch on its rump. He then walks and runs while repeating a call. Reproduction As with most shorebirds, the courtship behavior of the white-rumped sandpiper involves an aerial component. During courtship the male and the female fly upward side by side at an angle. At about above the ground they stop about apart and hover with shallow, rapidly vibrating wingbeats. The male remains above the female and repeatedly releases a series of "poing-zee" notes. They hover between 5 and 10 seconds before descending to the ground slowly and silently and land about apart. During their downward glide their wings are held together in a "V" position above their backs. A few minutes later they initiate a second paired flight identical to the first one. However, once they have landed on the ground the male begins to chase the female. The chase ends when the male does a wing raising display, which is common in many sandpiper species. The females are small and nest in the high arctic, which means they are more likely under a higher cold stress than birds nesting in temperate areas. Consequently, the females spend an average of 82.5% of their time incubating their eggs. In total, the females incubate the eggs for about 22 days. She generally lays 4 olive to green eggs; laying 3 eggs is rare. The eggs can sometimes be blotched with brown, olive-brown or grey spots. Only the females incubate the eggs. Once the female has laid the eggs, the male stops displaying and leaves the breeding grounds. This is unlike other members of the calidris genus where incubation is shared between males and females; therefore, the trait of male incubation has been independently lost in this species. There are only three documented species who have been known to share this behaviour. This development seems bizarre since experiments have shown that a decrease in the amount of male care is linked to a decrease in male fitness by lowering the number of male descendants that survive. One explanation for this evolution is that a decrease in male care allows the males to explore other breeding options.