Studying gosling behaviour
When I arrive at the field site, Suzanne Lubbe and Freya Hartog are just making a walk with the tame goslings.
There are two different research questions studied with these goslings:
1. Growth rate and behaviour in relation to vegetation type
2. Diet selection and digestion in relation to gosling size
The goslings are imprinted on Suzanne. They follow her everywhere and when she calls them, they run towards her. You can see a small video by clicking here. This following behaviour (imprinting) is not only fun, but also allows us to make detailed measurements and measure and weigh the birds regularly. By weighing the young after feeding for a fixed period on a given vegetation type, we have an index of goose value of that vegetation type. Fast growth means ideal, well digestible vegetation in enough quantity.
This is not always the case. as strange at is might sound, not every green plant is good goose food. Geese have a relatively simple digestive tract compared to e.g. ruminants (cattle) or hind gut fermenters (horses). Every leaf they eat, passes the intestinal tract in less than two hours. This is enough time to extract the cell content, but not enough time to break-down the cellulose and make it digestible.
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| Being a goose mother, means being out in the field seven days a week also in rainy and stormy weather. | Weighing the goslings is easy. We just place them on a kitchen balance. | At the end of the day, the goslings are placed in a cage |
Cellulose, the main component of the cell wals, forms 70% of the total energy of the plant material. Cellulose is a chain of glucose molecules (sugar). There is no vertebrate, who can break-down the chain of molecules by itself. Only bacteria have the possibility to gain enough energy to survive while breaking up the chain. To do so, they need to be in an environment without oxygen (anaerobic). How is a cow surviving on a grass diet? It simply cultures bacterial growth on the grass and eats the left-overs of the bacteria and the bacteria biomass itself.
To allow bacterial breakdown of the food, cattle have the food for 48 hours in their intestinal tract. There is no room for that in a goose. The geese only use the easiest digestible parts of the food and produce a dropping containing all the cell wals every 4-6 minutes.
What are the consequences?
a. Geese have to be very selective. They need the best digestable food, which is high in protein. This is usually the first growth in early spring.
By migrating north, the geese extend their spring and are using optimal food. But it also means that not all plants are potential food for geese.
b. Goslings are smaller than adults. They have also a smaller alimentary tract. The digestion might even be more difficult and the problem for
goslings might be substantial bigger than for adult geese.
c. Goose droppings contain cell wals. We can still determine the goose diet by analysing the cellwals under the microscope. Every plant is a different cellwall structure.
d. Goose droppings contain still food what can be used by large mammals. Reindeer eat goose droppings as it contains still lots of energy.
In a sparse arctic environment they can reach a high intake rate with only slighter less profitable quality food (for them).
Back to the experimental questions:
1. Growth rate and behaviour in relation to vegetation type
2. Diet selection and digestion in relation to gosling size
We are never touching the adult geese, but keep them constant in a cage and carry them around. They are adjusting to this routine and feed without problem, thus creating different treatments of the plots.
But the goslings, we can weigh easily and regularly. With this, we have a possibility to translate the benefits of the vegetation also to mass gain.
We have made the difference between adult geese and goslings into a research subject. At different ages, we are putting both the adult geese and the goslings and the same vegetation.
By comparing the quality of the food and the droppings, we can calculate digestibility.
By analysing the cellwalls in the droppings, we can analyse the diet.
