In little more than a month, the slender-horned gazelle population at the Sawa reserve plunged from 148 to 87.
Lack of funding, along with a shortage of rain, deprived them of food, as the country's drought dries up lakes and leads to declining crop yields.
President Barham Salih said tackling climate change "must become a national priority for Iraq as it is an existential threat to the future of our generations to come".
The elegant animals, also known as rhim gazelles, are recognisable by their gently curved horns and sand-coloured coats. The International Union for Conservation of Nature classes the animals as endangered on its Red List.
Outside Iraq's reserves, they are mostly found in the deserts of Libya, Egypt and Algeria but are unlikely to number "more than a few hundred", according to the Red List.
Turki Al Jayashi, director of the Sawa reserve, said gazelle numbers plunged by about 40 per cent in just one month to the end of May.
"They no longer have a supply of food because we have not received the necessary funds" from the government, Mr Al Jayashi said.
Iraq is grappling with corruption, a financial crisis and political deadlock, which has left the country without a new government months after October elections.
"The climate has also strongly affected the gazelles," which lack forage in the desert-like region, Mr Al Jayashi said.
At three other Iraqi reserves further north, the number of rhim gazelles has fallen by 25 per cent in the past three years to 224 animals, according to an agriculture ministry official who asked to remain anonymous.
He blamed the drop at the reserves in Al Madain near Baghdad, and in Diyala and Kirkuk on a "lack of public financing".
At the Sawa reserve, established in 2007 near the southern city of Samawa, the gazelles pant under the scorching sun.
The brown and barren earth is dry beyond recovery, and meagre shrubs that offer slight nourishment are dry and tough.
Some gazelles, including youngsters still without horns, nibble hay spread out on the flat ground.
Others take shelter under a metal roof, drinking water from a trough.
Summer has barely begun but temperatures have already hit 50ºC in parts of the country.
The effects of drought have been compounded by dramatic falls in the level of some rivers due to dams upstream and on tributaries in Turkey and Iran.
Desertification affects 39 per cent of Iraqi land, the country's president said.
"Water scarcity negatively affects all our regions. It will lead to reduced fertility of our agricultural lands because of salination," Mr Salih said.
He sent 100 million dinars (more than $68,000) to help save the Sawa reserve's rhim gazelles, Mr Al Jayashi said.
But the money came too late for some.
Five more have just died, their carcasses lying together on the brown earth.