Nicole K

Your Question: Who or what has been eating my Easter Eggs?

This week, the Discovery Centre was sent some pictures of Easter eggs. It's a sad story: they'd been gnawed, and not by their rightful owner (who was very interested to find out who the culprit was).

Gnawed Easter chocolates
Image: Anonymous
Source: Anonymous  

Usually we need to see a specimen or a photograph of an animal in order to identify it, but the chocolate thief had left behind a clue – teeth marks.

Gnawed Easter chocolate
Image: Anonymous
Source: Anonymous  

We sent the photographs to Museum Victoria's Senior Curator of Mammals. He examined the marks and reported that they had been made by the incisors of a small rodent, most likely a House Mouse, Mus musculus. His identification came with another sad story – his own chocolate Bilby had suffered the same fate!

A House Mouse, Mus musculus
Image: Rodney Start
Source: Museum Victoria  

Rodents have very distinctive teeth – a pair of incisors in the upper jaw and another pair in the lower jaw. The incisors grow continuously (like our fingernails), so rodents have to do a lot of gnawing to grind them down. In fact, the name "rodent" comes from the Latin words "gnaw" (rodere) and "tooth" (dentis). The gnawing process also acts to sharpen the incisors.

The skull of a House Mouse, Mus musculus
Image: Marnie Rawlinson, Cathy Accurso and Ken Walker
Source: Museum Victoria  

Wild House Mice are primarily granivorous (they eat grains and seeds), but they will eat almost anything. It seems that, like us, they love chocolate.

Happy Easter House Mice!

Got a question? Ask us!

Links:

Introduced Rodents

Collections Online: Easter

Your Question: Why are bird eggs so variable in their colours and patterns?

The colour and colour pattern of bird eggs vary enormously from species to species (and often between individuals of the same species, and sometimes between the eggs of the same mother).

  A tray of eggs from Museum Victoria's H.L White egg collection, showing the diversity of patterns and colours for a single species, the Australian Magpie Gymnorhina tibicen.
Image: Michelle McFarlane
Source: Museum Victoria  

Eggs are made of calcium carbonate, which is white. White is therefore the default colour for bird eggs, but many birds lay coloured or colourfully-patterned eggs. Why?

The colouration of bird eggs can often be explained by the animal's biology and behaviour. The eggs of ground-nesting birds, for example, need to be well-camouflaged to avoid discovery by predators. They are usually coloured and patterned to match the substrate they are laid upon.

The highly-camouflaged eggs of the American Golden Plover Pluvialis dominica, which nests on the ground.
Image: MeegsC
Source: Wikimedia Commons  

Tree-nesters, on the other hand, usually have blue or green eggs.

The American Robin, Turdus migratorius, which nests in trees, lays bright blue eggs.
Image: Laslovarga
Source: Wikimedia Commons  

Birds whose eggs are hidden from view (in hollows, burrows or deep nests), or who sit on their eggs continuously throughout incubation, tend to have white eggs.

  The now extinct Paradise Parrot Psephotus pulcherrimus, which laid its eggs in termite mounds, had white, unpatterned eggs.
Image: Rodney Start
Source: Museum Victoria  

The patterns on eggs have developed over eons via natural selection – the better the camouflage, the more likely the eggs are to survive and pass on the genes for well-camouflaged eggs to the next generation. Ornithologists have classified egg patterns and given each "style" a name in order to distinguish them: splashed, blotched, spotted, dotted, marbled, streaked, scrawled, overlaid, capped, and wreathed.

Eggs from Museum Victoria's Ornithology Collection
Image: John Broomfield
Source: Museum Victoria

Colour also provides another form of protection: it is thought to act as a sunscreen, protecting the developing foetus from UV light. The addition of colour also strengthens the eggshell. Birds that are calcium-deficient lay thin-shelled eggs, which are more likely to break. Scientists have found that birds that have multiple clutches in a single season have more highly-coloured eggs in the second and subsequent clutches (when the mother's calcium supplies are reduced). Patterned colouration is also more common in areas with calcium-deficient soils.

The specific colours are incorporated into the shell in the final stage of egg development. Blue and green colour comes from a pigment called biliverdin (which is the same pigment that causes green bruises in humans). In egg colouration, biliverdin comes from bile; the red and brown colour on eggs comes from protoporphyrins, which comes from blood.

The Red-vented Bulbul Pycnonotus cafer lays red eggs.
Image: J. M. Garg
Source: Wikimedia Commons  

Australia's native birds are protected. It is illegal to collect eggs or to interfere with birds' nests without a permit. Details of regulations and permits can be obtained from the Department of Sustainability and Environment.

Links:

Museum Victoria's Ornithology Collection

H.L. White Collection of Australian Birds’ Eggs

The evolution of egg colour and patterning in birds

Australian Magpie Eggs

Your Question: Why do scientists study animal poo?

Poo is truly fascinating stuff. Each deposit contains a minefield of information about its owner and the environment it lives in.

Animal poos (scats) come in a multitude of different shapes and sizes. Each species produces its own unique parcels. You can therefore discover which species are present in an area (and how abundant they are) by looking at what they leave behind.

The square droppings of a Common Wombat, Vombatus ursinus
Image: Alan Henderson
Source: Minibeast Wildlife  

The relative size of a deposit can also give you an idea of the age/size of he/she who dunnit. Sometimes, it's even possible to determine the sex and reproductive receptivity of the animal (by the smell).

The condition of the scat (taking recent weather conditions into account) will tell you how recently the animal was there – if it's still fragrant and sticky, you know you're fresh on the trail.

An animal's poo can also reveal the diet of the depositor. Long-term studies of scats can provide information about how animals' diets change over time and the seasonal abundance of their food sources.

A broken-up scat of a Thorny Devil Moloch horridus, revealing that it has fed exclusively on ants.
Image: Alan Henderson
Source: Minibeast Wildlife  

The scats of carnivorous (meat-eating) animals can be an invaluable source of information about the presence and abundance of their prey species. Fur, teeth and bones are not usually digested as they pass through the digestive system and come out relatively intact. As foxes and owls are far better at finding small animals than we are, scats can contain crucial records for scientists studying endangered species.

The scat of a European Red Fox Vulpes vulpes
Image: Karen Rowe
Source: Museum Victoria  

Poo is also a useful indicator of animal health. Scats contain parasites, hormones and DNA (in the animal's own skin and hair cells). Scientists can therefore use the clues in poos to monitor infections, perform genetic analyses and gather information on stress levels and reproductive state, all without touching or even seeing the animal.

Got a question? Ask us!

Links:

Square Poo

Dinosaur Poo