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Hibernation and migration

During the day and during the year, the activity of the organisms present maximum and minimum levels of intensity. Thus, the alternating periodsof activity and inactivity of the organisms were called biorhythms. The day-night alternation was called Circadian biorhythm (for example people's night sleep,day sleep ofbats in summer) andseasonal biorhythms (for example the hibernation in bats, the lethargic sleepof bears in Romania, bird migration).

We presentfurther the changes of activity of bats,with special reference to the bats in our countryand in Europe.

Their Resting Hours

In the temperate zone bats do not flyduring the day because they stay hidden in darkor dimly lit places, away from noise. Night shelters frequented by batsto rest can be caves,old tree hollows,abandoned houses bridges,steeples of churches, caves.
This period is essential for them to rest till the coming of night when they go out hunting. They rest during the day because of the high intensity of light and because of the high temperature. Diurnal rest is not yet complete.In maternity coloniesthere is bustling at any time.

Nocturnal Activity

Nocturnal activitiesactually begin duringthe twilight from evening and it is extended to morning. After awakeningfrom sleep bats execute short flightsinside the roosts. Only a few get out of the shelter at first, they makea short exploration flight, then return to announce the other members of the colony. If nights aretoo rainy and cold bats can temporarily give upthe feeding activity. Also, when leaving theshelter, they hunt for about 1-2 hours, after which they rest and digest just outside the roost, and they hunt again.

Migration

The phenomenon itself, of travelling to a long distance dueto the lack of food and to the change of the thermal regime,characterizes few species. For example, the flying foxes (Pteropuspolicephalus) migrate some 1000 km from Australia due to the reduction of food resources. Also interesting, are the migrations of Lasiurus species - Lasiuruscinereus borealis-moving on the routes of traveling birds, sometimes withthem, from the U.S. to Hawaii, to 4000km from the mainland.
Most species of insectivore bats do not migrate, butproduce an oscillation between their winter shelterand the summer. This shift has different causes: being close to food, to separate males from females during pregnancyand motherhood. The distance on the roadvaries from one species to another:

- Up to 35-40 km for weak flying species: the notched eared bat (Myotis emarginatus), the water bat (Myotisdaugbentonii), the whiskered bat (Myotis daugbentonii);

- Oftenover 100 km – the common large bat(Myotis myotis), the long-winged bat (Miniopterus schreibersii) the red evening bat (Nyctalus noctula).

Hibernation
Animal species are unable to maintain their constantbody temperature regardless of external ambient temperature changes. Therefore they reduce their vital functionsand enter a state of numbness.

After their internal temperature animalsare grouped into:

- Poikiloterms-invertebrate and vertebrate animals less developed (fish, amphibians, reptiles), with variable temperature.They are directly dependent of high ambienttemperatures (eg reptiles are calledcold-blooded animals, are heated in the sun). With the cold, they stop feeding andenter the state of total lethargy.

- Warm-blooded animals, are more evolved (birdsand numerous mammals) that have adapted to changes in temperature through the mechanisms of thermogenesis (heat production) and thermolysis(heat consumed soas to ensure high and constant internal bodytemperature regardless of the external ambient temperature).

- The Heteroterms - are represented by some mammals,which have the ability to adjust the intensity of metabolism according to the characteristics of the season. Thus, when it is hotand they have sufficientfood resources they have an intense metabolism. With winter coming, whenthey no longer have the means to feed, they greatly reduce their vital functions andenter into lethargy or sleep. This is the way the cahomeoterms behaveduring the summer and so are the poikiloterms in winter. The heteroterms in turnare divided into: hibernating (body temperature only dropsto 20 degrees Celsius, for example, the bear) andhibernating (body temperature can drop to 5 degrees Celsius frequently,sometimes even less). In the latter category are included theinsectivore bats.

For bats, hibernationperiods of about a month alternate with briefperiods of lethargy or awakening. Theseshort periods are necessary for individuals to change their place in the colony or inside the house,to hydrate. Duringhibernation, at a body temperature of about 5 degrees C, the oxygen consumption is only 0.02-0.07 ml/ g / h, or 1% of consumptionmade ​​during the activity. Survival isensured exclusively by fat accumulated duringsummer and autumn. A particular fatdeposit - brown fat- deposited on the shoulders, around the neck and on the sides of the body. This fat is a source of food but it also ensures the internal heat production (endothermic). If insectivorebats are forced to defend from the very low temperatures, other bats take steps to protect themselves from too high temperatures. Pteropus batsare nestled in foliageon trees andthey use their wings which they use as a fan to protect themselves.