The severity of the climate of Bulgaria in comparison with that of other European regions of the same latitude is attributable in part to the number and extent of its mountain ranges, in part to the general configuration of the Balkan Peninsula. Extreme heat in summer and cold in winter, great local contrasts, and rapid transitions of temperature occur here as in the adjoining countries. The local contrasts are remarkable. In the districts extending from the Balkans to the Danube, which are exposed to the bitter north wind, the winter cold is intense, and the river, notwithstanding the volume and rapidity of its current, is frequently frozen over; the temperature has been known to fall to 24° below zero. Owing to the shelter afforded by the Balkans against hot southerly winds, the summer heat in this region is not unbearable; its maximum is 99°. The high tableland of Sofia is generally covered with snow in the winter months; it enjoys, however, a somewhat more equable climate than the northern district, the maximum temperature being 86°, the minimum 2°; the air is bracing, and the summer nights are cool and fresh.
In the eastern districts the proximity of the sea moderates the extremes of heat and cold; the sea is occasionally frozen at Varna. The coast-line is exposed to violent north-east winds, and the Black Sea, the πόντος ἄξεινος or "inhospitable sea" of the Greeks, maintains its evil reputation for storms. The sheltered plain of Eastern Rumelia possesses a comparatively warm climate; spring begins six weeks earlier than elsewhere in Bulgaria, and the vegetation is that of southern Europe. In general the Bulgarian winter is short and severe; the spring short, changeable and rainy; the summer hot, but tempered by thunderstorms; the autumn (yasen, "the clear time") magnificently fine and sometimes prolonged into the month of December. The mean temperature is 52°. The climate is healthy, especially in the mountainous districts. Malarial fever prevails in the valley of the Maritza, in the low-lying regions of the Black Sea coast, and even in the upland plain of Sofia, owing to neglect of drainage.
The mean annual rainfall is 25-59 in. (Gabrovo, 41-73; Sofia, 27-68; Varna, 18-50).
Few special features are noticeable in the Bulgarian fauna. Bears are still abundant in the higher mountain districts, especially in the Rilska Planina and Rhodope; the Bulgarian bear is small and of brown colour, like that of the Carpathians. Wolves are very numerous, and in winter commit great depredations even in the larger country towns and villages; in hard weather they have been known to approach the outskirts of Sofia. The government offers a reward for the destruction of both these animals. The roe deer is found in all the forests, the red deer is less common; the chamois haunts the higher regions of the Rilska Planina, Rhodope and the Balkans. The jackal (Canis aureus) appears in the district of Burgas; the lynx is said to exist in the Sredna Gora; the wild boar, otter, fox, badger, hare, wild cat, marten, polecat (Foetorius putorius; the rare tiger polecat, Foetorius sarmaticus, is also found), weasel and shrewmouse (Spermophilus citillus) are common. The beaver (Bulg. bebr) appears to have been abundant in certain localities, e.g. Bebrovo, Bebresh, etc., but it is now apparently extinct. Snakes (Coluber natrix and other species), vipers (Vipera berus and V. ammodytes), and land and water tortoises are numerous.
The domestic animals are the same as in the other countries of southeastern Europe; the fierce shaggy grey sheep-dog leaves a lasting impression on most travellers in the interior. Fowls, especially turkeys, are everywhere abundant, and great numbers of geese may be seen in the Moslem villages. The ornithology of Bulgaria is especially interesting. Eagles (Aquila imperialis and the rarer Aquila fulva), vultures (Vultur monachus, Gyps fulvus, Neophron percnopterus), owls, kites, and the smaller birds of prey are extraordinarily abundant; singing birds are consequently rare. The lammergeier (Gypaëtus barbatus) is not uncommon. Immense flocks of wild swans, geese, pelicans, herons and other waterfowl haunt the Danube and the lagoons of the Black Sea coast. The cock of the woods (Tetrao urogallus) is found in the Balkan and Rhodope forests, the wild pheasant in the Tunja valley, the bustard (Otis tarda) in the Eastern Rumelian plain. Among the migratory birds are the crane, which hibernates in the Maritza valley, woodcock, snipe and quail; the great spotted cuckoo (Coccystes glandarius) is an occasional visitant. The red starling (Pastor roseus) sometimes appears in large flights. The stork, which is never molested, adds a picturesque feature to the Bulgarian village.
Of fresh-water fish, the sturgeon (Acipenser sturio and A. huso), sterlet, salmon (Salmo hucho), and carp are found in the Danube; the mountain streams abound in trout. The Black Sea supplies turbot, mackerel, etc.; dolphins and flying fish may sometimes be seen.