Last time I talked about spotted sandpipers and sequential polyandry, but I did not mention that the males and females are very similar in appearance i.e. they lack sexual dimorphism. For many birds that are monogamous, the males are usually much showier in appearance than the females i.e. they are sexually dimorphic.
Spotted Sandpipers are not sexually dimorphic because their breeding plumage is grey or brownish with spotted breasts and blends in well with their natural environment. So, they are well-hidden in the surrounding vegetation. They also bob their tails up and down which helps to disguise them against moving water.
However, many bird species do exhibit sexual dimorphism. In monogamous birds the females must remain well hidden while they are sitting on the nest brooding eggs and feeding the chicks.
Males often have more obvious markings and brighter colouration. This is not only to attract the attention of females they wish to mate with, but also as an advertisement to other males that they are more attractive.
Wilson’s, red-necked and red phalaropes are not only sequentially polyandrous but also are sexually dimorphic.
It is the males that are left to sit on the nest, hatch the eggs and feed the young so they must blend in well with their environment. They lack the brighter colours found in the females.
The females attract a male, copulate with him, lay eggs in his nest and then go off and look for another male to breed with and so their plumage is brighter to show off and attract the males.
Another fascinating feature of phalaropes is that they are often seen spinning around rapidly on the surface of water. It is thought that the spinning creates a vortex in the water forcing food items to move up in the water column toward the surface where the birds can reach them more easily.
Wilson’s phalaropes are the most common ones seen here, but red-necked phalaropes do pass through our area heading north and occasionally stop for a rest here on our ponds and lakes. Red phalaropes are Arctic breeders and unlikely to be seen here.
