MEXICO CITY — The number of heat-related howler monkeys deaths in Mexico has risen to 157, the government said, with a tragically small number of the primates treated or recovering. Meanwhile, an animal park in northern Mexico confirmed it has received reports that at least a hundred parrots, bats and other animals have died, apparently of dehydration. A heat dome — an area of strong high pressure centered over the southern Gulf of Mexico and northern Central America — has blocked clouds from forming and caused extensive sunshine and hot temperatures all across Mexico. Last week, environmentalists had reported that 138 of the midsize primates, known for their roaring vocal calls, had been found dead in the Gulf coast state of Tabasco since May 16. Almost two-thirds of the country are expected to see highs of 45 degrees Celsius on Monday. …But with heat, fires, and deforestation hitting the trees where the howler monkeys live, it was unclear whether even releasing them could ensure their survival.