Climate, Landscapes and Vultures

Climate, Weather and Relief. Climate is a very important issue for vultures. This section will look at the daily weather regimes, namely thermal creation, times for roosting and average temperatures that affect movements; seasonal climate regimes that affect migration and breeding schedules; and climate zones that influence vulture distribution. Firstly we look at the components of climate most important to vulture ecology: climatic regions, temperature, rainfall, wind and seasonal change.

Climate is defined as the average weather conditions—precipitation, temperature, humidity, pressure, wind over usually at least 30 years. Weather refers to these variables over the short-term; anything from a few minutes to a time-frame approaching that climate. Weather is determined by altitude, latitude, marine proximity and orientation of mountain barriers to ocean currents and winds. A climatic region is determined by the particular combination of five environmental components; the atmosphere (air), hydrosphere (water), cryosphere (soil), land surface, and biosphere (plants).

The study of past climates, termed Paleoclimatology uses parameters such as lake bed sediments, ice cores, tree rings and coral. Three climate classification schemes in common use for modern climates are the Koppen system, the Thornthwaite system and the Bergeron and Spatial Synoptic Classification. Classification systems have been criticized as being too rigid as they imply distinct boundaries between different zones, rather than gradual transitional areas.

The Bergeron classification used air masses for classification, using three letters; the first letter for moisture properties (c) for continental air masses (dry) and (m) for maritime air masses (moist); the second letter for the thermal characteristic of the source region (A) for Arctic or Antarctic, (E) for equatorial, (M) for monsoon, (P) for polar and (T) for tropical; and the third letter for the stability of the atmosphere. Air masses warmer than the ground below are (w); those colder than the ground below are designated (k).

The Spatial Synoptic Classification system (SSC) is based on the Bergeron classification scheme. This system has six categories: Dry Polar (similar to continental polar), Dry Moderate (similar to maritime superior), Dry Tropical (similar to continental tropical), Moist Polar (similar to maritime polar), Moist Moderate (a hybrid between maritime polar and maritime tropical), and Moist Tropical (similar to maritime tropical, maritime monsoon, or maritime equatorial).

The Koppen classification uses average monthly values of temperature and precipitation. The common version has five categories: A, tropical; B, dry; C, mild mid-latitude; D, cold mid-latitude; and E, polar. These can be divided into secondary classifications such as rainforest, monsoon, tropical savanna, humid subtropical, humid continental, oceanic climate, Mediterranean climate, steppe, subarctic climate, tundra, polar ice cap, and desert.

Relief, also termed terrain, refers to elevation, slope, and orientation of features on the earth's surface. Relief is very important for vultures, because it affects climate. Climates become colder with altitude; thus species that prefer cool weather and climate nest or forage on high mountains or plateaus. There is also the rain shadow effect, as high mountains may block rain-bearing clouds from large areas such as the American southwest, creating a desert or dry savanna climate. Relief also channels wind according to the shape of the landforms, creating orographic windflow that may be useful for foraging soarers. Large, flat plains may also produce large thermals for these soarers during foraging. As was noted in the first three chapters, many vultures also nest in inaccessible cliff caves or crevices high in the mountains, hence their distribution is largely influenced by mountain presence. As terrain affects water flow and distribution, it also determines river and sea coast patterns, affecting those vultures that feed on animals frequenting such areas.

From the perspective of vultures, all the climate categories are valid except for subarctic climate, tundra and polar ice cap. Rainforests have high rainfall, with definitions setting minimum normal annual rainfall between 1,750 mm (69 in) and 2,000 mm (79 in). Mean monthly temperatures exceed 18°C (64° F) during all months of the year. A monsoon is a season with a rain bringing wind that may be dominant for several months, almost always in the tropics and often in rainforest regions.

Tropical savanna is a biome with varying proportions of grasses, shrubs and trees; wetter savannas have more trees, drier savannas have more grasses. Savannas are usually located in semi-arid to semi-humid climate regions of subtropical and tropical latitudes, with average rainfall between 750 millimetres (30 in) and 1,270 millimetres (50 in) a year and temperatures above 18°C (64°F). These are common in Africa, South and Southeast Asia and northern South America where they form the intermediate landcover between forest and desert. A steppe is a dry grassland with few or no trees. In the temperate zone of Eurasia and North America (in the latter steppe is usually called prairie) the annual temperature range is high; in the summer of up to 40°C (104°F) and during the winter down to -40°C (-40°F). In Africa, the Sahel savanna, a dry transition zone between more moist tree savanna and the Sahara desert, broadly corresponds to the steppe.

A desert usually exists in regions that receive minimal precipitation and therefore few plants exist. Due to the very low humidity, deserts generally have large seasonal and diurnal ranges in temperature; day temperatures may reach 45°C (113°F), and night temperatures may go down to 0°C (32°F). Many deserts exist due to the rain shadow behind mountains that block the moisture bearing winds from the ocean or more moist landcover.