Animal Responses to Tropical Environments: Life Histories of Tropical Birds - Essay Example

Full Name of Student) (Full Name of Teacher/Professor) (Subject) (Date of Submission) Animal Responses to Tropical Environments – Life Histories of Tropical Birds Introduction While many species of animals do thrive in different environment in many parts of the world, humans have long been fascinated by birds because of their colorful and aesthetic appeal. Continuous ornithological studies have become more interesting as each species gather intriguing characteristics one from the other. This report discusses the life history and behavioral pattern and characteristics of birds in relation to their specific adaptability to environmental conditions. Some of the most interesting birds can be seen in the tropical regions where climate is most unfavorable for their existence. But there are also birds that thrive in the temperate zones that are also worth looking into. Tropical regions are located on the equatorial belt and experiences hot and humid weather from time to time. The convection of air within these regions causes too much precipitation and there is an abundance of rainfall. There are seasons that thunderstorms do occur simultaneously but this belt also receives sufficient sunshine and more than enough rainfall thus the existence of lush vegetation. The weather could not be easily distinguished as cold or warm. All regions covered by tropical climate have two existing seasons, wet and dry season ("Enclyclopedia of Atmospheric Environment") . North Temperate Zone is usually characterized by a warm climate in the summer which was suited for animal habitation and mild to extreme cold in the winter brought about by the northerly winds. North American temperate rainforest are commonly found in the humid west coast. Several endemic animals can be found in temperate regions because of their highly specialized habitat requirements. Usually these animals are indicator species of the said region. One of the most prevalent and mobile creatures thriving in these areas were birds that already adapt themselves with the change of their environment (Broker).. Food limitation As agile and active creatures, birds have to rely on the availability of food in their ecosystems and limited food is equaled to their limited reproduction in the wild. Generally, food limitation is one great factor that influences the lifespan and attentiveness of some birds to their eggs and young. In Argentina, for example, certain species are feeding their nestlings properly as compared with the inattentiveness of birds of the same species in Arizona. Although obviously there is an abundance of food in the wild of Arizona than Argentina, the birds in Argentina devote more time incubating and caring for their eggs and young than their Arizona counterpart. Nest Predation There is an inter-specific variation in clutch size and parental care activity within birds of Argentina and Arizona. The incubation period and nest predation among birds in these two different localities also varies. It was observed, however that nest predation is higher in the south and the latitudinal pattern is not the primary cause of nest predation. Nest predation varies among types of nest. The most affected factor concerning latitudinal variation is adult mortality. On some species of birds in the tropics, predation risk was higher on nests that have been established early in the wet season. Successful nests were those made late in the wet season, thus contrary to earlier hypotheses, time of breeding is not the real reason behind escaping nest predation. Nest predation among tropical birds usually happens at 80-90% most for different species. Predation risks also vary depending on the season. Other birds such as Clay-colored robins breed when food is scarce to avoid peaks on egg-laying and constrict nest predation. Nest predation in the tropics differs with every habitat, time of year and also altitude. Many tropical species, however, do not have temperate zone counterparts which is somewhat difficult to assume the real score on nest predation but can only be supported through predation frequency. Nest predation in the tropics is high because of the high abundance and diversity of predators such as snakes, opossums, and other small mammals. Temperate zones have lower nest predation as compared with tropical birds. Age specific mortality It was observed that some birds timed their laying of eggs and nestling period during the spring where some insects are becoming in abundance. Species that lay eggs earlier than this season usually suffer nestling mortalities. Severe seasons like winter in the northern temperate zones have greater adult mortalities among adult bird species as compared with the southern tropical regions. Adult mortalities greatly influence reproductive cycle not only in terms of productiveness, but also in terms of effort by the parents and the risk in caring for the young. To avoid mortalities some species capable of long flights usually migrate during the shifting of weather conditions. But non-migratory birds especially from most part of southern latitudes reduce their mode of reproduction in order to produce small clutch size. The experiments made in Argentina and Arizona showed that southern parents were less willing to care thus creating more young mortality. This is because adults with low mortalities exhibit reduced nest attentiveness to control the size of their numbers into maximum existence (Martin). Breeding seasons Tropical birds tend to breed all the time because of the favorable conditions in their area. Frugivorous birds (fruit-eating birds) prefer to breed during dry season to commensurate on the availability of food while insectivorous birds breed during wet season. Breeding season last for 4 to 8 months and coincide with the abundance of fruit and insects as well as in reducing pressure from predation. Although many of the ancestors of most of the temperate bird species come from the tropics, the birds on the temperate zone have very short breeding period because of the limitation of food which usually last for 2-3 months. Tropical and temperate migratory birds have different social behavior and time of breeding. Favorable conditions can enhance favorable breeding period among tropical birds but surprisingly, not all species are able to follow certain order in breeding and only breed during specific time of the year. While in temperate zone, breeding was more accurate and significant and eventually always timed for mating season. Clutch sizes In the tropics smaller clutch sizes and weights of nestling is also brought about by the scarcity and lower delivery rates of food during dry season and so nestlings tend to grow slower as compared with nestlings of the same species in the temperate zones. Nest predations also have an impact on the mortality of the young which makes up to 30% in dry season and 72% in the wet season. Clutch sizes usually range from 2 eggs in the humid neo-tropics to 4-6 eggs in the high northern latitudes. There are some tropical species which does not show latitudinal variation in terms of clutch size, however. These are the gannets, crossbills and ravens. Other birds have even unusually large clutches. While in temperate zones, food limitation hypothesis suggest that latitudinal locations which makes up for a longer day length allow temperate zone birds to gather more food thus allowing parents the energy to produce eggs and feed their young. Feeding rates in the temperate zones are very high while day length is shorter in the tropics. Shorter feeding period is a hindrance in having a bigger clutch size and nestling starvation causes young mortalities. Incubation periods In the tropics, songbird parents do reduce nest attentiveness to reduce their own risk of mortality during incubation period. Lower attentiveness is characterized by longer incubation period. This practice varies from regions, latitudes and in species. Incubation time and nestling period is longer in the tropics and the fledged young remain dependent on their parents for many months. This is favorable for the young to prolong its immaturity and dependency to its parents. Tropical birds lay eggs according to how many they can raise which result in high adult survival but small clutch size. Temperate birds however though have a shorter time for its incubation period produces bigger clutches, very active in feeding their young and also have shorter fledging period. Adult survival The adult survival rate was achieved based on re-sightings and recaptures of breeders. Accordingly, tropical birds though have high nest predation also have high adult survival as compared with temperate birds. Again, favorable condition in the tropics has a great role in the longer life span of tropical birds. This factor has an impact on their behavior such as in choosing a mate and in the acquisition of its territory. Extra-pair mating systems for tropical birds although being practice by some birds of the temperate zone, is being supported favorably by climatic conditions in the tropics and mating simultaneously is common. Molt and mating systems The mating systems also differ according to species and climatological conditions. Temperate birds show high level of testosterone during mating season thus their testis are relatively larger than normal. This is also true among polygamous species of birds. High testosterone level increases their attractiveness among female birds. Monogamous birds sometimes switch to extra-pairing. Tropical birds even during mating season have normal testosterone level. This suggests that testosterone level is not always the requirement for territorial defense and attraction for mate as were previously concluded. Therefore, high testosterone levels among birds of the temperate zone imply that they are only adapting themselves for mating competition to compensate for the short temperate breeding season. This is one evolutionary process of adapting themselves with the environment to continue their existence. Tropical birds do not show seasonality in breeding and so they have two to three times longer mating period than temperate birds. Their mating season is also unpredictable. North temperate bird species generally breed on the months of May-July because of climatic constraints and shortage of food supply. Hypotheses also explain that breeding season is also affected by seasonal molting. There are also tropical evidence that molting is generally avoided during times of the year when food is not in abundance. This explains why the timing of breeding must be timed with molting. There is no direct evidence, though that indicates molting determines breeding seasons although it does force birds to end breeding even there is food abundance (Stutchbury and Morton). Evaluation of hypotheses explaining differences In conclusion, the following table identifies the discovered hypotheses in relation to the characteristic displayed by tropical and temperate birds. Table 1. Summary of Findings Tropical Birds North Temperate Birds testosterone levels remain normal even during mating season High testosterone level during mating season Testis remain normal in size even during breeding period but continue to show aggressiveness in mating and territorial defense Enlargement of testis for mating competition and only show aggressiveness during mating season Majority of the species breed almost all year round – 6.6 to 9.8 months Breeding season usually lasts from 3.1 to 4.2 months Some species have unpredictable breeding season Land birds usually breed at the same time Monogamous but sometimes switch to extra-pair mating Mostly are monogamous but certain females do produce offspring from other males Greater selection of mates Limited selection and sometimes females do pair with a single male for life Have longer life span Short life span as compared with counterparts in the tropics Minimum adult mortality Greater adult mortalities because of winter Reduced nest attentiveness and prolong incubation period among other species Optimum nest attentiveness Breeding for some species is unpredictable Breeding time is more accurate Smaller clutch sizes with 2-4 eggs per clutch Clutch sizes ranging from 6-8 eggs for some species Do not show seasonality in mating Have 2-3 months mating period usually during May-July Work Cited: Read More