DAVAO CITY (MindaNews / 15 October) — The dead eagle found along the shoreline of Maasim town in Sarangani last September 16, 2022 is disturbing. It is not the first. It is the third Philippine Eagle that crashed in the same sea. But if we look at the eagle rescue records for Mindanao, it is already the 8th case on the island.
Philippine Eagles should not be at sea for three reasons. First, it is strictly forest-dwelling. It is designed by nature to live only inside the forest.
Second, fish is not its food. Other eagles, like the White-bellied sea eagle, Osprey, Gray-headed fishing eagle and the Brahminy kite, eat fish. But Philippine Eagles eat only mammals, birds, big lizards and snakes.
And lastly, its wings and body plan are not fit for over-water flights. They do have large and broad wings, but these are built for catching and riding columns of hot air rising above the land (thermal updrafts). They glide from one thermal to the next, and they rarely flap their wings. This is a survival strategy as doing so saves them energy. But out in the sea where thermals are unstable at best, they risk crashing and drowning.
Thus, if a Philippine Eagle ends up at sea, it is most likely not of their own making. But what can push these animals to these unsuitable areas?
Could it be human persecution? Were they flying away from people who want to shoot or trap them? But between forests they are capable of navigating and where they can ably find cover, and the sea which they are not adapted to, there is certainly higher mortality risk at sea.
Also, eagles seem to be poor at avoiding and fleeing from human dangers. In one rescued eagle for instance, X-ray showed 10 air gun pellets embedded at different parts of its body. These pellets accumulated from different shooting attempts. Also, the Philippine Eagle Foundation (PEF) retrieved a total of 14 eagles on Mindanao since the pandemic began in 2020. Ten or 71 % of these were due to human harm.
The eagle’s evolutionary history explains its inability to cope against human threats. As the top carnivore of the Philippine tropical rainforest, the species evolved without any natural predator. As a result, they lack natural fear of other animals.
Then our kind came. We are a new comer as a biological species, but we dominated the earth instantly. The eagles and similar apex predators had very little opportunity to evolve their counter-strategies against our impacts because we became so invasive in a geologically short span of time.
The lack of human fear is even stronger among inexperienced juveniles and immature eagles. For instance, out of 63 rescued eagles whose age are known since the 1970s, 50 birds or 79 percent were juveniles or immature eagles. These birds were either trapped, shot or harmed by people.
What about lack of food? Will the eagles willfully leave their natural forest habitat if they can’t find their usual prey species? They do fly great distances in search for their prey. But in tracking food, the sea is definitely not an option.
Or could it be disease perhaps? The eagles that crashed at sea might have been sick, which compromised their ability to fly and navigate efficiently. But rather than being mobile and taking the air, we know that sick eagles are lethargic and will stay on their perch. A sick and weak eagle in the forest, therefore, could not make it that far out into the sea.
If it is not human persecution, nor lack of food, nor disease, what can be a possible explanation to these sea crashes?
We think that in all of these cases, the eagles reached the seas by accident. And that these mis-navigations were influenced together by air and wind patterns and the location of the eagles’ habitat relative to coastal areas.
Philippine Eagles navigate the skies through thermal updrafts – rising columns of hot air over the land. They glide and circle into and out of these columns to move through the landscape. As an energy-efficient strategy, they evolve to become obligate soaring birds that glide and rarely flap their wings.
But for eagles moving along the base of the mountain close to the coast, the series of thermals could lead them closer and closer to the sea. And along the coast, they are prone to gliding farther out into the open water. Unfortunately, thermal updrafts are weak over water, if not absent.
In this dire situation, the eagle could have shifted from gliding to flapping and, given the distance it has to travel back to land, got exhausted, lost altitude and eventually crashed into the sea.
The wings and muscles of a Philippine Eagle are not built for power (flapping) flights, unlike those of sea eagles, ospreys, and many migratory raptors.
Land breeze (winds moving from the land to the sea) perhaps might also influence the movement of gliding eagles away from land. Land breeze is strongest during early mornings and at night when the sea heats up faster than the land. But since eagles are only active during daytime (diurnal), land breeze might impact eagles that for some reasons are already active on the wing during early mornings.
Only the immature eagles fly long distances during its dispersal stage. Thus, eagles of this age bracket (2-5 years old) are very vulnerable to sea mishaps. In contrast, sexually mature, paired and territorial adults who fly and move only above its forest home range are not as susceptible.
All of the eight eagles retrieved from the sea based on PEF records were immature birds.
If these sea crashes are accidental, what can we do to prevent them? Awareness campaigns in coastal communities close to forest habitats is very important. Of the eight Mindanao cases, seven were successfully rescued by concerned fishermen who saved the poor birds from drowning.
But a more proactive approach is a combination of nest search and monitoring, and telemetry study of young Philippine Eagles in the wild. We need to locate as many territorial eagle pairs as possible through systematic nest searches across the country and faithfully monitor the breeding of each pair. The Department of Environment and Natural Resources (DENR), PEF and academic research institutions, together with trained community forest guards can jointly do this.
Then, once active nests are located and monitored, install radio and GPS trackers on as many juvenile eagles as possible before they leave their parents’ territory and roam.
By instrumenting birds with transmitters, we can monitor where they go and intervene when needed. A miniature GPS tracker strapped back-pack style on each young eagle will give conservationists the means to follow each bird remotely via the internet. Attaching a radio (VHF) transmitter to the side of the GPS unit, on the other hand, will allow homing-in and finding the birds when needed.
Every time the bird’s safety is compromised (e.g., flying close to villages or along the coast) as seen from the Google Earth or GIS maps of its daily GPS fixes, a team can be dispatched to follow the bird and ensure safe passage. Listening to and tracking the beeps of the radio transmitter using a hand-held receiving device will guide the team to the bird’s exact location.
The PEF team and trained forest guards have done this for several eagles and the proactive monitoring spared the birds from shooting, trapping, and other threats in the wild (see the stories of eaglesSinabadan, Kalabugao, and Raquel).
Every individual of the International Union for Conservation of Nature (IUCN) “critically endangered’ Philippine Eagle is precious. Through the creative combination of technology, technical expertise, collaboration and grit, we can save young eagles not only from the perils of the sea, but also of from the many dangers that these innocent birds face in the wild. The national government, through the DENR, must invest more to locate, monitor and save our gravely imperiled national symbol.
(Jayson C. Ibanez, PhD, is Director for Research and Conservation of the Philippine Eagle Foundation – a conservation NGO whose mission is to save the Philippine Eagle from extinction)
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