World Migratory Bird Day丨As a migratory bird that is almost "forgotten", why is the migration route of the relict gull so different?

Produced by: Science Popularization China

Author: Li Bo (Shaanxi Institute of Biological Agriculture)

Producer: China Science Expo

The autumn wind blows and the white clouds fly, the grass and trees turn yellow and the geese fly south.

Since ancient times, the Chinese have believed that migratory birds must fly south of the Qinling Mountains and the Huai River to spend the winter. Familiar geese, swans, swifts, wild ducks, etc., all follow this route to migrate north and south with the change of seasons.

Figure 1

(Photo source: Veer Gallery)

But there are always exceptions. Today I would like to introduce to you a bird that does not follow the beaten path - the relict gull.

The forgotten bird

The relict gull (Larus relictus) belongs to the genus Larus in the family Laridae of the order Charadriiformes. The word Relictus means "forgotten" in Latin. The name of this bird is quite poetic. But its discovery is a tortuous story.

In April 1924, ornithologist Ejnar Lönnberg, then director of the Swedish Museum of Natural History, discovered a bird in a place called Congduoer (Mongolian, meaning "a place with lush red willows") in Ejin Banner in western Inner Mongolia, China. The bird was about 40 cm long, with a dark brown to black head, the upper edge reaching the back of the neck, and a white neck; the waist, upper tail coverts and tail feathers were pure white. Because of its appearance similar to that of the black-headed gull (Larus melanocephalus), Lönnberg initially believed that this was an oriental geographical population of the black-headed gull.

Later, after careful observation and thinking, Lönnberg felt that this might be a new species that had not yet been recognized by the world. However, due to his cautiousness in academic research, he felt that it was too hasty to draw conclusions based on a single specimen. So, later that year, he published another article to raise this question and cryptically named it Larus relictus, which means "Lost Gull".

Since then, the relict gull has entered the field of scientific research. The bird has now become the model specimen of the species and is preserved in the Natural History Museum in Stockholm, the capital of Sweden.

Figure 2 Relict gulls living in Hongjiannao, Yulin

(Photo credit: Wang Qingxiong, Shaanxi Institute of Zoology)

Although the relict gull was given a name, the international ornithological community has been controversial about its taxonomy in the following decades: some believe it is a variant of the brown-headed gull (Larus brunnicephalus); others believe it may be a hybrid of the fishing gull (Larus ichthyaetus) and the brown-headed gull...

In the zoological community, reproductive isolation is an important condition for defining a valid species. However, this must be supported by a large amount of ecological data. In addition, the taxonomy at that time was mainly based on morphological characteristics. The morphological characteristics of the relict gull (especially during the breeding season) are highly similar to those of many gulls, and the scarcity of specimens also makes morphological identification unconvincing. In this way, the severe lack of specimens and ecological data of the relict gull has made its classification a long-standing unresolved issue in the ornithological community.

It was not until 1971 that Auezov, a former Soviet ornithologist, proposed that the relict gull should be considered a valid species based on a small independent breeding population found in Lake Alakol in Kazakhstan and the specimens collected. Only then was the relict gull truly accepted as an independent species by the world.

Where is home?

Although the mystery of the Relict Gull's origin has been solved, where are the Relict Gulls distributed on the earth? How many of these birds are there? What are their living habits? These questions are still confusing...

In order to find the answer, ornithologists focused on the vast deserts and Gobi in Central Asia and the Mongolian Plateau and conducted many years of searches. It was not until 1987 that the mysterious relict gull was discovered again in the Ordos region of Inner Mongolia. On the island in the middle of the inland lake Tao-Ahaizi, scientists discovered the world's largest relict gull breeding ground at that time. In order to effectively protect this species, the local government established a relict gull nature reserve on the spot. By 1998, 3,600 pairs of relict gulls had come to the island to breed, exceeding 60% of the total known relict gull population in the world at that time.

Today, this place has become the Ordos Relict Gull National Nature Reserve and has been listed as an internationally important wetland by the United Nations. Since then, relict gull nature reserves have been established in Yulin, Shaanxi, Zhangjiakou, Hebei, Xilinhot, Inner Mongolia, and other places.

Figure 3 Xiao Hong, a researcher at the Shaanxi Institute of Zoology, has been conducting research on relict gulls at Hongjiannao for 20 years.

(Photo source: Xinhua News Agency, Tao Ming)

The establishment of the reserve has provided a guarantee for the survival of the relict gull and created conditions for scientists to carry out systematic research. Since then, work on the ecology and population biology of the relict gull has been carried out one after another. Through research on the reproductive biology, habitat selection and composition of bird communities in the relict gull's breeding grounds, scientists have discovered that the relict gull is a unique bird species that has adapted to the desert and semi-desert conditions of the Mongolian Plateau.

At present, there are four main independent populations distributed around the world: the Central Asian population centered on Lake Alakho and Lake Balkhash (Kazakhstan); the Gobi population scattered throughout the central and western parts of the Mongolian Plateau and down to the southern Gobi ; the Far Eastern population with lakes and wetlands at the Far Eastern border of China, Russia and Mongolia as its breeding grounds; and the Ordos population distributed in the Ordos Plateau and surrounding areas.

Figure 4 A pair of relict gulls during the breeding season

(Photo credit: Wang Qingxiong, Shaanxi Institute of Zoology)

In addition to clarifying the distribution of the population, the living habits of the relict gulls are also gradually being understood by humans. They practice strict monogamy and mainly build nests on the ground in clusters on lake islands in plateau desert and semi-desert environments. The egg-laying period is generally from March to May each year. After the first egg is laid, it will sit in the nest and incubate, with the parents taking turns to incubate the eggs.

Generally, about 60 days after hatching, the weight and length of the young birds are close to those of the adults, and they have strong flying ability. Compared with other gulls, the young birds of the Relict Gull grow slowly, which may be related to the variety and abundance of food in the growing environment. When the lakes begin to freeze in winter, they will migrate in groups to overwinter, and return to the breeding grounds in the spring of the following year. This cycle continues endlessly.

Figure 5 Newly hatched chicks on the island in the middle of Hongjiannao Lake

(Photo source: Xinhua News Agency, Tao Ming)

Where to fly?

Although the breeding grounds have been discovered, the exact location of the relict gull's migration routes and wintering grounds has always puzzled ornithologists. In nature, most migratory species have relatively fixed migration routes and wintering grounds. If this information is missing, it means that we cannot carry out effective monitoring and protection of the non-breeding stages of their life history.

Since the relict gulls breed in the heart of the Asian continent, they can choose different directions and routes to overwinter: fly east to the coast of China; fly west to the Caspian Sea and the Mediterranean Sea; or go south to the Indian Ocean. In order to find out "where do they go in the winter", in early studies, scientists put metal rings on the young relict gulls in the breeding grounds, but the effect was not ideal. The marked young relict gulls have been observed sporadically in the southeastern coast of China, the Korean Peninsula, Japan and even Vietnam.

But where exactly the large populations of adult birds went remains a mystery.

Figure 6 A sub-adult relict gull foraging on the salt lake beach in Dingbian County

(Photo credit: Yang Yaqiao from Shaanxi Institute of Zoology)

It was not until the beginning of the new century that this mystery gradually surfaced with the help of the application of GIS and satellite positioning technology, the improvement of field observation technology, and the participation of more and more bird lovers. During 2003-2006, a large number of adult relict gulls were found in the coastal areas from Hangu, Tanggu to Dagang in Tianjin, and their number was basically consistent with that of the Ordos population.

At this point, ornithologists have roughly outlined a migratory route for the relict gulls, which starts from central and northern China and flies along northern North China to the Bohai Bay. The distribution pattern of the wintering population, centered on the coastal mudflats of the Bohai Bay and radiating to the Yellow Sea and the East China Sea, has also gradually become clear.

In order to survive the cold winter, these clever birds chose the most economical migration route, which goes almost due east and due west, and came to the coast of the Bohai Sea to recuperate.

Figure 7 Adult relict gulls wintering in Bohai Bay

(Photo source: China Bird Watch, photo by Liu Yang)

Where does the road ahead lead?

Despite its unattractive appearance, the Relict Gull, one of the latest birds discovered so far, has become a Class I protected animal in my country and a vulnerable species of the International Union for Conservation of Nature (IUCN). The reason why a species becomes endangered may come from its own characteristics, such as a specialized way of survival, or there may be external reasons, such as the degradation and loss of habitat. Unfortunately, these two Relict Gulls have both.

The reproduction of the relict gull must rely on lake islands in desert and semi-desert environments, and this fragile habitat is increasingly affected by global climate change. In the past decade, the continued drought in the Mongolian Plateau and the increased demand for groundwater resources by humans have greatly affected the breeding grounds on which the relict gull depends for survival. The area of ​​a large number of inland lakes, represented by Hongjiannao, is shrinking. In addition, with the needs of economic development, the impact of human activities in the Bohai Bay area on the wintering grounds of the relict gull is also increasing...

Millions of years of evolution have made the relict gulls a "lone hero" in the desolate desert. In order to reproduce, they have been persisting in the difficult journey of survival from east to west. Year after year, winter turns to spring, and the birds experiencing the changes of time and space are also struggling to adapt to the various changes brought about by humans and nature.

In order to allow them to survive for a long time and not become "forgotten birds", there is still a lot we need to do.

Editor: Sun Chenyu

References:

1. He Fenqi et al. Overview of the study on the relict gull. Journal of Zoology, 2002, 37 (3)

2. Liu Yang. Relict Gull: From the Gobi Desert to the Bohai Bay. China National Geographic, 2008, 11

3. Zhang Wei et al. Analysis of distribution types and ecological environment characteristics of the relict gull. Journal of Inner Mongolia Normal University, 2017, 46 (05)

4. Wang Qingxiong et al. The brooding behavior and chick growth of the relict gull in Hongjiannao, Shaanxi. Journal of Zoology, 2013, 48 (3)

5. Wang Qingxiong et al. Incubation behavior of relict gulls in Hongjiannao. Journal of Ecology, 2103, 32 (2)

6. Liu Yang. Relict gulls fly eastward. China Bird Watch, 2012, 84(02)

(Note: Latin parts in the text should be italicized)