Bird Answers

by Deb on February 3, 2012

Birds of Paradise

How did you do? I had good fun working out the answers.

1.     Lungs in birds are very different to ours, they are more efficient. In mammals we breathe into large dead end sacks of alveoli, use some oxygen then have to get rid of the low oxygen air taking up the space. Birds let air flow continuously through their lungs and get oxygen from fresh air on both in and out breaths. This constant supply of fresh oxygen helps give birds the extra energy needed to fly.

There are two main functional differences to make it happen, extra air sacs and tubes for air exchange rather than little balls like mammals. When a bird breathes in, some of the air goes through the tubes to give it oxygen and some goes into air sacs. When they breathe out, the air sacs are emptied and the air goes out through the tubes as well. It’s easier to see with a diagram:

Bird breathing

Modified from Vet. Res. 37 (2006) 311-324

When they breathe in, oxygen rich air splits and goes directly into sacs 3 and 4 or through the lungs then into sacs 1 and 2. When they breathe out all the sacs are emptied. The oxygen rich air stored in sacs 3 and 4 goes out through the lungs and the air they’ve already used in sacs 1 and 2 goes straight out. It’s ingenious and far more efficient than our own breathing.

2.     Birds can’t sweat, so they need to cool down differently to us. One way is though panting, evaporating the water in their mouths uses energy and cools them down.

Hot birds (I have lots in the desert) hold their wings open or drop them to encourage air flow around them. Heat is related to volumes and surface area – warm-blooded animals create heat throughout their volume, but lose it through their surface. So by spreading out their wings birds greatly increase their surface to get rid of the heat.

And some birds like chickens or honeyeaters have fleshy combs and wattles. These look red because they are full of blood and very thin skinned. Apparently if you squeeze them you will actually get drops of blood out, but it isn’t something I’ve tried on my chookens.  The air flow around them cools the blood, that can help cool the rest of the body. They work the same as an elephant’s ears.

3.     Kiwis have the biggest egg of any bird relative to their body size. It’s so enormous female kiwis have trouble walking before laying it and have to fast, they were lucky they could survive that way. Fortunately they had no predators prior to human settlement in New Zealand. Mammals such as cats, rats and possums never made it to New Zealand so the females could afford to be awkward without risking their lives.

kiwi egg

Kiwis are ratites, the group of flightless birds that includes ostriches, emus and New Zealand’s extinct moas. Like lots of biological things, there is a fairly predictable relationship between the size of a bird and the size of the egg they lay. However the ratites don’t fit on this nice line very well, their eggs are too big. Then Kiwi eggs are big even for ratites.

But, kiwis only lay one egg. If you look at the relationship of clutch size, rather than egg size, kiwis are in just the right place. Rather than putting energy into lots of chicks and hoping some of them make it, the lack of predators allowed them to put all their energy into just one well-developed chick and give it a better chance.

4.     The Dodo was a large, flightless, ground-dwelling bird in Mauritius, closely related to pigeons. It shared many features with Kiwis not because they are related, but because they fill similar ecological niches. Once again, their island home did not have cats, rats, pigs and humans, which allowed them to stop flying.

Dodo

We're not even certain what it looked like, there are very different reconstructions.

Humans discovered Mauritius and its Dodos in 1598, and by 1700 they were all gone. This was probably not because of direct human hunting – even though it was easy to catch, no-one seems to have liked the taste very much. But introduced animals and deforestation finished them. It is possible that they were already in trouble as a small, isolated population, however there is no doubt that humans ultimately caused their extinction.

The Dodo is probably the first extinction of the modern era, and it is an important lesson not just of what we can do, but how we do it. Three hundred years later we still aren’t killing most animals ourselves (except for fish), but the pets and hitchhikers we take along and our insatiable appetite for land makes us responsible for their deaths.

5.     The boys up the top are all different types of Birds of Paradise, and they are all showing off for the girls. One of the arguments people used against natural selection was that some animals have features that are detrimental to their survival, like enormous tails or bright colours that make them targets for predators – shouldn’t they be dead? Darwin had a brilliant answer to this and it is its own sub-theory and rather large field – sexual selection.

Basically, natural selection is not about survival, it is about reproduction. In my own words, he who dies with the most grandkids wins. Females have it a bit easier than males because they produce the eggs so generally they are guaranteed to at least be in the race. It might be more difficult and dangerous for them to produce babies, but they will definitely have the chance to do it. Boys have the easy job as far as babies are concerned, but they might not even get to do that much. It’s a simple truth that not every male gets to become a father, a few particularly good ones grab all the girls.

In some animals the competition is between males, in others it’s more dangerous to be male and they have a higher death rate. But some animals pair up through female choice, and that’s when the boys go all out. No-one knows what starts females down a particular path – how did the bright colours or fancy dancing or singing or gifts get started? It’s probably fairly close to random. But once it’s started males tend to get more and more extreme, because if everyone has a little bit you have to have more to stand out.

Then they are stuck in a delicate balancing act – you have to be able to survive until adulthood but then get as many mates as you can. Too extreme and you might die, too boring and you won’t leave any descendants. Pity the poor peacock, carrying an enormous tail to entice the ladies. It almost makes high heels look sensible.

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