The American bald eagle: On eagle’s wings

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Isaiah 40:31 instructs us that those who wait on the Lord will renew their strength, mounting up or soaring on wings like eagles. This majestic image reminds us of God’s effortless ability to refresh and restore us. Yet this passage is also an acknowledgement of the wonderful abilities our Creator has given the eagle, which mankind has consistently associated with power, swiftness, and independence.
eagleSekar Balasubramanian/123RF

The eagle features prominently in the heraldry of various cultures, where in addition to symbolizing strength and freedom, it also represents courage. Out of all the varieties of eagle, arguably the most visually striking and well known is the American Bald1 Eagle (Haliaeetus leucocephalus; ‘white-headed sea-eagle’). As both the national animal and bird of the United States of America, it appears on its presidential and national seals.

The bald eagle is indigenous to North America and can be found near any kind of wetland habitat or large body of open water where there is an abundant supply of fish. Bald eagles mate for life and build large eyries or nests, typically within 200 m (700 ft) of their chosen water source, though they can be as far as 3 km (2 miles) away.2 Good nesting trees usually have the following characteristics: height (to provide protection for eggs and young eaglets); visibility of the major food source (the body of water); and sparse foliage (allowing for an open flight path to and from the nest). While eyries are typically placed 15–40 m (50–130 ft) above ground, they can be positioned much lower where trees stand in water (such as mangroves), or even on the ground.3 They are the largest tree nests recorded for any animal species: up to 6 m (20 ft) deep, 3 m (10 ft) wide and weighing more than 2 tonnes (4,500 lb).4

Bald eagles will remain in one location year-round, provided there is always access to open water and no human interference. However, birds located near water sources that freeze over in winter migrate south or to the coast. Well known locations include Squamish in British Columbia, in Canada, and the Alaskan Chilkat Eagle Preserve, where thousands of bald eagles gather to feed on spawning salmon.5

Diet of the Fallen

manlius/123RFeagle-nest

However, the bald eagle doesn’t exclusively eat fish. When less fish are available, they will target other birds (especially water birds), small mammals, snakes, turtles, and crabs. They also scavenge carrion, and bald eagles are known for stealing meals from other raptors (in particular, the osprey).6

But the bald eagle was not always a carnivore; rather, this is a result of the Fall. Originally every green plant was given for food to the eagle kind (along with every other living thing that has the breath of life in it) by God (Genesis 1:29–30). Some birds that might be expected to be carnivorous because of their anatomy include the palm nut vulture7 and the totally vegetarian oilbird.8

A Marvel of Design

These birds are a marvel of lightweight structural design.9 Each one has more than 7,000 feathers that weigh a mere 500–600 g (about 20 oz) in total. The skeleton, constructed from hollow bones, is half that weight, just 5–6% of the animal’s total weight.10 The wings, spanning over 2.4 m (8 ft) in the female, make excellent use of any updrafts or thermals to ascend effortlessly without wasting energy by flapping. Tail feathers are spread to provide the largest possible surface area, and wide separation of the tapered wingtip feathers helps reduce turbulence and further assists soaring ability. Feather positioning and structure enables drag to be increased or reduced as required. It also keeps the bird warm and waterproof. Underneath the flight feathers is a layer of down. Air can be trapped in pockets beneath the feathers to assist with insulation. By simply changing the position of its feathers, the eagle can regulate its body temperature.

A bald eagle can reach some 70 km/h (45 mph)11 when gliding or flapping, and can fly with a maximum load of nearly 7 kg (15 lb), a record for any living bird.12 When hunting fish, they swoop down and snatch them out of the water with their powerful talons. Diving speeds up to 160 km/h (100 mph) can be reached.13 The wing has to be strong to slow the bird rapidly as it prepares to grab a target, then continue flight with the extra load. Structures on the toes called spicules allow the talons to grasp slippery prey. The gripping power of the bald eagle talon is estimated to be ten times greater than that of a human hand, exerting upwards of 2.75 MPa (400 psi).14 Tiny ridges on the tendons and tendon sheaths can interlock, creating a ‘ratchet’15 effect. This enables the eagle to maintain tremendous pressure on the talons without continuously applying the enormous contraction force on the muscle.

Gregory Johnston/123RFgliding-eagle

Eagle eyesight is renowned, being 4–5 times stronger than our own (likened to seeing an ant crawling on the ground from the roof of a 10-storey building).16 The bald eagle eye is very large compared to the head size, roughly the same ratio as our own, providing a large imaging area on the retina. Each eye has two foveae, whereas humans only have one.17 The fovea is responsible for sharp central vision, and contains the type of photoreceptors, known as cone cells, responsible for colour vision. One of the eagle’s foveae is directed forward, the other to the side. This enables very precise distance perception. The eagle’s foveae also have five times the density of cells than those of humans, and its vision extends into the ultraviolet spectrum of light, which is invisible to humans.18 Adult bald eagles can also correct for refraction (the bending of light when it passes between air and water) when catching fish.

eagle-flyingJoseph Fuller/123RF

History or story-telling?

Bald eagle numbers have been threatened in the past, with only 417 nesting pairs left outside of Canada and Alaska in 1963.19 However, with the assistance of conservation efforts, the population rapidly rebounded to nearly 6,500 nesting pairs in 2000.20

Notice how quickly the numbers increased. It is easy to see how just one pair of the created kind from which the bald eagle is descended (not pairs of every currently known eagle or other raptor species) dispersing from the Ark after Noah’s Flood could spread out rapidly across the earth and increase in number. Eagle speciation occurred as existing genetic traits came to the fore due to adaptation and selection in differing environments. Thus the various species of eagle (and likely at least some of the other raptor species such as hawks) we see today all trace their ancestry back to the pair that emerged from the Ark.

The evolutionary account, though, requires a staggering exercise of farfetched speculation. Part of this story says that birds evolved from reptiles, with Archaeopteryx, a true bird, still trumpeted by many as a transitional fossil and ‘dated’ as living 140–150 million years ago.21 The earliest known fossil said to ‘closely resemble’ the bald eagle is dated at 1 million years old; however, it is acknowledged that no one knows exactly when the bald eagle first appeared (according to evolutionary reckoning).22

Rather than this just-so story of how life came to be without our Creator, we recognize that the bald eagle has always belonged to the same kind, as originally created by God on the fifth day of the Creation Week. We can still marvel today at His amazing design capabilities when we watch the bald eagle soar on high.

References and notes

  1. From the early English word balde which meant ‘white-headed’. Return to text.
  2. Travsky, A., and Beauvais, G.P., Species assessment for Bald Eagle (Haliaeetus leucocephalus) in Wyoming, p. 8, November 2004, blm.gov. Return to text.
  3. Bald eagle, wildflorida.com/wildlife/birds/Bald_Eagle.php, acc. 21 May 2015. Return to text.
  4. Largest bird’s nest, guinnessworldrecords.com/records-10000/largest-birds-nest, acc. 21 May 2015. Return to text.
  5. Bald eagle viewing, baldeagleinfo.com/eagle/eagle1.html, acc. 21 May 2015. Return to text.
  6. The term ‘raptor’ comes from the Latin rapere, kidnap, grab by force. It generally means birds of prey with keen eyesight, strong curved beaks and grasping talons, and includes eagles, hawks, and some types of vultures. Return to text.
  7. Catchpoole, D., The ‘bird of prey’ that’s not, Creation 23(1):24–25 December 2000, creation.com/vegetarian-vulture. Return to text.
  8. Bell, P., The super-senses of oilbirds, Creation 28(1):38–41 December 2005, creation.com/oilbird. Return to text.
  9. Doolan, R., Created to fly! Creation 16(3):10–14 June 1994; creation.com/created-to-fly. Return to text.
  10. Eagle description, baldeagleinfo.com, acc. 21 May 2015. Return to text.
  11. Bald eagle Haliaeetus leucocephalus, ct.gov/deep/cwp/view.asp?q=325972, 21 May 2015. Return to text.
  12. Amazing bird records, trails.com/arts/amazing-bird-records.aspx, acc. 21 May 2015. Return to text.
  13. Bald eagle info, baldeagles.org, acc. 21 May 2015 Return to text.
  14. Gripping strength of an eagle, hawkquest.org, acc. 21 May 2015. Return to text.
  15. That is, until the tendons and tendon sheaths unlock, the talon won’t open. It can only move in one direction, which is to close. Return to text.
  16. Wolchover, N., What if humans had eagle vision? livescience.com, 24 February 2012. Return to text.
  17. Biology-Structure and anatomy, eagles.org, acc. 21 May 2015. Return to text.
  18. Bald eagle, learner.org/jnorth/tm/eagle/Vision_part1.html, acc. 21 May 2015. Return to text.
  19. Ref. 2, p. 3. Return to text.
  20. Ref. 2, p. 33. Return to text.
  21. Sarfati, J., Birds: fliers from the beginning, Creation 29(3):27 June 2007, creation.com/archie. Return to text.
  22. Bald eagles’ evolutionary ancestors, pbs.org, acc. 21 May 2015. Return to text.