Walk Softly – Jaws vs. The Birds!

by Geoffrey Carpentier

Last time, I explored the reptiles and amphibians, to determine how they use their jaws and teeth (or non-teeth) to capture or harvest food. Today, we’ll look more closely at birds and how they use their beaks to hunt and eat. All birds have beaks – this is indisputable, but the size, structure, shape and use of them varies considerably between groups of birds. Beaks come in many forms: hooked or curved, cone-shaped, needle-like, spatulate and even crossed!

Finches, such as the goldfinch, have large conical bills designed to grasp and crush seeds which form the bulk of their diet. The size of the seed they prefer is somewhat linked to the size of the beak, how wide it opens and their Bite Force Quotient (BFQ - is the force they exert when biting down on something). An Evening Grosbeak can exert about 25lbs pressure, when it tackles cherry seeds, one of its favourite foods. The finches must use their beaks to not only break open the outer shell of the seed, but also to husk it and retain the tasty innards which form the bulk of their diet. One family of finches, known as the crossbills, have extremely specialized beaks which are curved and cross over each other side-to-side and are designed to pry open the seeds from the cones of conifers. One would expect a robin, which consumes soft fruits and invertebrates, would exert much less pressure. It does, but I couldn’t find a reliable source to tell me its BFQ.

Parrots have large heavy beaks which can break open huge seed pods or fruits, to get at the juicy food inside. Hummingbirds have uniquely adapted beaks which both allow them to eat tiny insects and, most importantly, lap up nectar from feeders or plants. One other strange adaptation is the beak of the skimmer, a gull-like bird, which has mandibles of different lengths. The lower mandible is longer than the upper, so they can drag the beak through the water and catch small invertebrates or fish and swallow them whole.

Many other birds do not rely on their beaks to break food items open but, rather, use their beaks to tear off tiny bits which are then swallowed and processed in the stomach. Chickadees are good examples of this feeding strategy.

Frugivores (fruit-eaters), who don’t have powerful crushing jaws and beaks, will just manoeuvre the fruit in their beaks until the flesh can be swallowed and the seed either spit out or ingested whole and ‘pooped’ out later. Called granivores (i.e. seed-eaters), these birds rely on seeds for all or most of their nutrition. Many gamebirds, such as grouse, feed by picking up small seeds, then temporarily holding them in their crops, where they previously ingested small stones to help grind up the food, before it is swallowed and further processed in the stomach.

Predators have differently adapted beaks which are designed to hold prey and tear it apart. They have a small hook on the end, to help break the flesh open so they can grip it and tear it into bite-size pieces. They don’t grind the food up, but rather just swallow the smaller pieces. Some fish-eating birds, such as mergansers, have a different strategy when it comes to their beaks. They have sharp fringes along their length which allow them to hold the fish in a manner akin to vice grips. This ensures the slippery fish can be held long enough so it can be manoeuvred in a head-down position and swallowed whole. There is a group of birds, called prions, who live in the southern oceans. They have tiny lamellae (fringes) along the length of their bills, but these are soft and act very much like the baleen of some of the large whales. The prey (and some water) is drawn into the mouth, and the water is expelled through these fringes, but the food is captured behind them, to be swallowed whole. This is just a tiny look at the complex feeding strategies of birds. Next time we’ll look at mammalian feeding strategies.

Geoff Carpentier is a published author, expedition guide and environmental consultant. Visit Geoff on-line on LinkedIn, Facebook and Instagram.