When the dry dipterocarp forest of Yok Don National Park in Dak Lak Province enters its deciduous period, it is the ideal time to take avian photos. 

Yok Don National Park resembles a European forest during its dry deciduous period, as depicted by Ngo Vu Thang's photo. 

There are more than 12 ranger stations in the park, ensuring conservation of the forest ecosystem is well-taken care of. Rangers here pay special attention to the prevention of forest fires in the dry season. Unlike tropical forests, evergreen forests, jungles or mangroves, Yok Don is the only dry dipterocarp forest remaining in Vietnam with attributes similar to temperate forests. 

Every year from December to February, leaves turn bright yellow, then in March, cover the ground until May, and when the rainy season begins, the trees again start sprouting. 

The ecosystem of Yok Don includes more than 89 species of mammals, 305 species of birds, 48 ​​species of reptiles, 16 species of amphibians, hundreds of freshwater fish species and thousands of species of insects.

A male crested treeswift is taking care of its two-week-old baby at Yok Don. 

This small bird, pictured by Ngo Vu Thang, is about 20 centimeters tall. The male has a light brown face and upper neck with a long crest and long gray wings. The female looks similar to the male except for the light brown parts on its face and neck. 

Yok Don is rich in bird species, with the typical being black-headed woodpeckers, red-breasted parakeets, Indian rollers, small minivets, common myna, crested treeswifts, and rare waterbirds like white-winged ducks, giant ibis or woolly-necked storks.

A rare bird species in Yok Don is the woolly-necked stork, with a wingspan from 75 to 91 centimeters, slightly smaller than other species in the stork family. The bird has a black spot on top of its head, shiny black wings and body in contrast to the white neck and a dark red beak. This species live in spacious wetlands and on forest edges.

Vo Rin, who has captured 405 bird species in Vietnam on his camera, said: "This species is shy of people, if you want to take pictures, you have to wake up very early. At around 4 a.m., I moved to the area where they usually feed then camouflaged myself carefully and waited until when the birds started feeding there to take photos. This photo was taken when the birds finished feeding and were flying low."

The crested serpent eagle is a popular species in Yok Don, with a wingspan from 51 to 71 centimeters. They inhabit mountainous areas and nest from January to October.

"In the afternoon, I observed the bird perched quite high in a tree, until 3 p.m. I saw it again and this time it perched on a lower branch for a long time, with its back facing the camera lens, about six meters away. It was a rare moment so I took a photo right away," Vo Rin said.

One of the most impressive bird species in Yok Don is the spotted owlet. This is a small owl species, about 20 centimeters long and that preys during the day. It has dense white brows, big yellow eyes, a white lower body and upper body with many white spots and brown stripes on its chest.

Photographer Nguyen Thuy Linh said when she observed the spotted owlet perched on a branch, it was preparing to fly away. Luckily, she took a shot of this moment in time.

The Indian roller, pictured by Vo Rin, is a common species in Yok Don. A full grown Indian roller has a wingspan around 17 to 20 centimeters. 

In Vietnam, this species is also distributed in Ma Da Forest (Dong Nai Province), Cat Tien National Park (Dong Nai), Tram Chim National Park (Dong Thap Province) and Can Gio mangrove forest (HCMC).

Yok Don has 17 species of woodpecker, including the black-headed woodpecker. This is a large size species in the woodpecker family, with a height of 33 centimeters. 

The female has a black head and lime-yellow neck. The male is similar to the female but has a bit of red on the top of its head. This species often frequents tree stumps and holes to look for termites. The photo was taken by Ngo Vu Thang.

The chestnut-vented nuthatch has a medium size in the nuthatch family, at about 13 centimeters long. The bird has a gray head and upper body with a black stripe, while its lower body is yellow with many white tail feathers. The female looks similar to the male though the color of its lower body is paler.

Nguyen Thuy Linh said it was difficult to take a photo of this bird because of its small size and fast pace when it searches for prey. 

Yok Don National Park is located on relatively flat terrain, at 200 meters above sea level, in Krong Na Commune, Buon Don District, 40 kilometers to the north of Buon Ma Thuot Town.

In recent years, along with the management and protection of nature and biodiversity, the park also organizes many ecotourism and environmental education activities. 

Popular services include experiences with elephants, camping, bird watching, walking, cycling in the forest or taking a boat on Serepok River. Tourists could also visit villages near Yok Don like Jang Lanh, Drang Phok or Buon Don to learn about the unique culture of the Rade, M'nong or Vietnamese of Lao origin.

Touring the forest in the deciduous season and learning about birds are among the most popular ecotourism activity, with the price of VND500,000 ($22) per person for a three-hour tour.

Tourists should go between mid-February and the end of April, when the dry season hits its peak. The forest trees enter the deciduous phase to cope with the dry weather of the Central Highlands, making it easier to observe and photograph birds.