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The term "Raptors" derived from a Latin word "rapere" meaning taking by force and those classified within this group are predatory and "birds of prey" is a another term used by ornithologist on a specific families of predatory birds. So the Raptors that we are talking about are predatory and also in stricter term some of them, birds of prey.
But not only the Raptors, many other species of birds do spend over half the year away from their breeding areas. We are more familiar with northern winters, these birds spent the other half on the years on migration to and from their the wintering ground. Hence, there is an area for breeding and another for their winter times. The combined migratory journey of these birds simultaneously is one of the most impressive phenomena in animal history which bring us to the point of "Raptors Watch"
Scarcity of food during the cold season is the primary reason that most raptors leave their breeding territories in winter. Then why do they need to return in the spring to breed has yet to be solved. There could be many factors, with the vast grasslands there is lower disturbance and parasite populations and longer days for hunting. Perhaps is the abundant food supplies which will increase the breeding success in the temperate zone. Here is Malaysia, our forest is the most southern end of the migration route. The Raptors reaching here are more of the grassland species from the temperate zones.
In some species of raptors, every individual migrates. In other species, only part of the population migrates and some individuals remain on the breeding grounds. Other species are completely sedentary. Overall, about 45 percent of all raptor populations migrate.
Then we must also remember that Raptors, influenced by food sources and nesting needs are extremely territorial. Needing a fixed area for their living needs. During the migration, these particular needs are all set a side and they fly and hunt within close proximity.
Now first have a look at the sketch for the Eastern Hemisphere, involved in this migration are Land birds, Waterfowls, Shore & Wading birds, Sea birds and lastly the most dramatic of all Birds of Prey. This page focuses on one, the Birds of Prey.
For winter migration the most northern points would be Zhalong National Nature Reserve in western China and the Shiretoke National Park in Northern Japan. Those following the former route would stay close to the coastline and all the way down to Malaysia then across to Sumatra or south through Singapore to the Rhio archipelago.
For some species, those 1st year wintering Raptors merely months out of the nest, are making their first long haul south. They followed the routes used by adults but differs only in the duration of the journey.
There are many watch sites along the route making the total of 380 sites world wide. For winter migration, Radar Hills and Pencil In Chumphon Thailand are the most active watch sites while in Malaysia, it's the Scotts Hill in Taiping.
How do the birds fly and get their bearing? Birds of prey do not waste important resources like energy to accomplish their epic journey. Instead they adopt one of the several method to progress daily towards their destination.
In their migration route, Raptors do not like crossing large bodies of water. Simple reason the monotonous water level do not create up drafts. More preferred are land routes and shorelines which navigate around large bodies of water. Thus because of the profile of the coastline, certain geographical locations become concentration spots. The raptors gathered passing through an narrow corridor prior to dispersing back into a wider corridor. Chumphon at the Isthmus Of Kra is one such example, the low hill in Tnagjong Tuan is a lesser example.
The most commonly used tactic would be to use mountain ridge systems. They are not good for visual guidance but more importantly the hot air generating air currents consequent to the solar heating of the valleys and slopes. Then by the upward deflections of the northwest winds. A thermal is a mass of rising hot air produced by the intense heating of the forest. This usually comes about on the south side of a mountain slope due to its position in relation to the autumn sun. The thermal would take the raptors thousands of feet in the sky. No flapping or the wings, just get lifted and glides. Knowing the conditions of the thermal, the Raptors would then switch to gliding in circles. This way the bird capitalized on techs strongest effects in the thermal which lifts them to higher altitudes. Up to a point, the bird would then venture straight into a southerly direction and disappear into the horizon.
The other method of travel used by the Raptors would be to capitalize on the deflective air currents that is brought about by a windy day. For example, a horizontal northwest wind strikes the north slope of a mountain and then is forced upward creating strong up-drafts. raptors on their way south would get a convenient ride on this updrafts. Suddenly the Raptors is soaring upwards at unprecedented speed up along the slopes. Quite a change from their normal gliding pace to an amazing speeds surpassing 60 miles per hour. Another observations is that the stronger the wind, the closer the Raptors will fly close to the treetops. A scene very common in Pencil Hills. This is no air turbulence but mere wind pushing the bird forward and despite of the speed the bird shooting past quickly, it is clearly seen and photographed.
On the contrary, when ever a high pressure system exist in the area, the Raptors would disperse over large areas. This would be the time they take the opportunity to do their hunting while awaiting for the weather change, an increase in wind speed and the existence of a thermals. Usually this high would somehow moves eastward, then a southerly airflow moves in. The raptors are back on their journey re-joining the newly created updrafts along south facing slopes.
In the roosting are when there is rain or fog, the birds cannot fly when there is no "lift". We see them high up on raining days as they are riding above these wet areas.
The best time of the day to Raptor Watch is generally between the hours of 9:00 am. and 2:00 pm. when the lift are generally created via the heated earth. In Bukit Kiara and along the coast at the Mangrove forest, that is also the timing. On isolated incidence, I had seen strays started searching for thermal on a sunny morning as early as 7.30am.
For those of you not that familiar with Raptors, spotting and ID the birds flying swiftly across the bright sky as background is rather challenging. If the Raptors are passing overhead in low altitude or in the early hours when they just left their place of roost and are seeking thermal, with the naked eyes, it is easy to make out their relative size and the body profile in flight. The ID could straight away be determined. Then a pair of good field glasses could help in clarifying the markings to sort them into male, female or juvenile on their 1st Winter outings.
After a few days of practices the task becomes clearer, more so if there is an experienced birders nearby giving advice. Getting to know the birds better and ability to get involved with their process get many addicted. These are also the same birders who kept returning each year to participate over and over again.
Beside this winter migration, there is the return trip done in reverse. This is the Spring Migration done in a shorter time frame during the months of March, April and May. The routes back are near identical, due to the profile of the terrain running in reverse, the location of the Watch Sites are completely different.
There are points for Winter migration and other points for Spring migration. The few sites were selected after years of observation and found to be productive and representative of the worth watching and memorable event. The watch sites are strategically position where the Isthmus Of Kra is the narrowing of the land passage where all birds have to be funneled through while the Malay Peninsula is the final destination and also the turnabout points. For the winter migration there are 2 watch sites, one in the mainstream Isthmus and another sample site along one of the many diverse trail adopted by the Raptors.
Then in the Spring Migration, the watch site at Tanjong Tuan capture the inevitable crossing of the seas, in this case a short but focused cross-over point, another funnel along the route the Raptors are taking on their way home to the breeding grounds in the north.