Snowy Plovers


What are Snowy Plovers?

The Snowy Plover Charadrius nivosus, is a small shorebird that can be found at sandy beaches and salt lakes of North and South America. In Spanish they are called chorlito nevado (or sometimes chorlo nevado). The locals also call them fantasma de la playa which means 'beach phantom' because their white/light brown plumage often melts perfectly with the colors of the beach substrate. 

Distribution and Taxonomy

Snowy Plovers are restricted to the Americas. There are three geographically distinct Snowy Plover groups (or subspecies) that differ in plumage and their genes: the subspecies nivosus which can be found in continental North America, subspecies tenuirostris which is found on a number of Caribbean Islands and subspecies occidentalis which is distributed along the Pacific coast of South America from Colombia to Chile. Until recently Snowy Plovers were considered to be part of the Kentish Plover Charadrius alexandrinus which is found in the Old World. But genetic analyses including DNA samples from our Ceuta plovers showed that they warrant to be called a species of their own right [1].

The Snowy Plover has three closely related cousins on other continents: the Kentish Plover in Eurasia and North Africa, the White-fronted Plover Charadrius marginatus  in Sub-Saharan Africa and the Red-capped Plover Charadrius ruficapillus in Australia. Some taxonomists also consider a fourth cousin the endemic Javan Plover Charadrius javanicus which is found in Indonesia and Malaysia. However, it is still debated whether this plover is a species on its own itself. All these closely related plovers look pretty similar and have similar behavior although they can be identified through their calls and in the laboratory when DNA sequences are compared.

Appearance, Habitat and Lifespan

Snowy Plovers are relatively small terrestrial birds. The adults weigh about 30-60 grams and have a lengths of 15-17 cm [2].

Most bird books will state that adult males and female Snowy Plovers differ in their plumage. However, these differences are not very strong and only appear during the a short window of the breeding season. During this time males have incomplete black breast-bands, black eye-stripes, and a black frontal head bar, whereas these areas are rather dull brown in females. Some females have dark brown / blackish breast-bands and frontal head bars to make things more confusing. On top of this the black ornaments slowly wear off and therefore it is often hard to tell whether a male is really a male or a female a female. During the non-breeding season the black parts of the plumage become brown and males and females look alike.

Despite being good flyers Snowy Plovers spend most of their lives on the ground. They live at sparsely vegetated and sandy beaches or dried salt flats in lagoons, both of which are found at Bahía de Ceuta. Snowy Plovers are visual hunters and feed on terrestrial and aquatic invertebrates which they find in marshes, on tide flats and around the high water line at the beach. Depending on the geographic location Snowy Plovers migrate in Winter to the South or they stay year around in the same area. Northern populations and those from the US interior usually migrate to the Pacific or Gulf of Mexico. Many of these plovers stop at Bahía de Ceuta. The plovers in Mexico stay year round.

For a small bird Snowy Plovers can become quite old. The oldest Snowy Plover to date recorded was a male that reached an age of at least 15 years [2].  The average lifespan of a Snowy Plover is 3-5 years.

Breeding

The time and length of the breeding season vary locally but generally last from late January to September. Males establish territories and start digging a number of scrapes with their legs in their territory. As soon as a female approaches the male will make itself as big as it can by puffing up the white chest feathers and courts the female. If the female is interested in the male and /or the territory it will visit a number of nest scrapes and join the nest scraping activities. Now the pair has formed and male and female will then defend the territory against other intruders together.

The nest is a simple scrape on the ground and the parents collect bits of plants, pebbles, shells and even salt crystals to fill it for thermo insulation or decoration. The female usually lays three eggs in the nest, which hatch after about 25 days of incubation. Both the mother and father take turns sharing the hard work of incubation (biparental care), with females incubating mostly during the day and the males working more often at night. After the chicks hatch, parents lead them away from the nest and defend them for at least three weeks until they are able to fly and survive themselves. Snowy Plovers produce multiple clutches during a season and pairs can stay together or switch the partner between breeding attempts. If they are looking for a new mate or a good place for breeding they can travel long distances. There are several cases in which color banded Snowy Plover females were recorded at different nests a few hundred miles apart within the same year.

What makes them interesting?

So, why do people care about these birds and have studied them for years? Well, there are at least two reasons. First, Snowy Plovers have an interesting family life which is full of conflicts. For example: Who should care and for how long? Generally both parents work together during incubation and look after the eggs until the chicks hatch. But then often one parent deserts the brood to find a new partner and start a new family. The remaining parent is left alone to do the hard work of bringing up the young. Fortunately, the chicks are precocial that means they do not rely on food to be brought to them. A few hours after hatching chicks are able to run and will look for prey themselves. In Snowy Plovers both parents are capable to care or desert but females desert more often than males. Whether both parents stay together and care for the young or one of the parents deserts and which parent will desert is hard to predict. At Bahía de Ceuta usually the female deserts the brood to re-mate, but the pattern is different in other populations. 

One of our goals is to work out what makes the male or female parent desert or stay and for this we study plovers at different locations all around the world. From other populations it is known that pairs usually stay together if there are many dangers for the chicks. Females are also more likely to remain with the brood at the end of the season when it is more difficult to find a new mate [3]. But these factors do not explain all variation in parenting what we see. Understanding this variation may also help to solve the mystery of cooperation, a question that has been high on the science agenda for the last years.

The second reason to work with Snowy Plovers is conservation. Snowy Plovers have become threatened over the last decades and they need to be better protected. Particularly the Pacific populations in North America have been declining severely. The main reasons are probably habitat destruction and increased beach use which is disturbing the plovers when they are resting, feeding or breeding. The Pacific coast populations of the United States are listed as threatened by the U.S. Fish and Wildlife Service [4] and since 2011 the Snowy Plover is also strictly protected in Mexico. Studying and understanding the needs of Snowy Plovers better is important to figure out better ways to save them from extinction.