The Brown rat (Rattus norvegicus), is also referred to as the Norway rat, Pouhawaiki, Sewer rat, and Water rat. In New Zealand it is dominant in urban areas and near waterways and human habitation. It is far less common in bush and forested areas.
Weight
Typically 200g - 300g (up to 450g)
Thick, with pale underside:
Comparison of R. rattus (top) and R. norvegicus (bottom):
Comparison of R. norvegicus top, R. rattus bottom:
Comparison of R. norvegicus and R. rattus ear hairs - sometimes R. norvegicus ears are described as 'hairy' and R. rattus ears are described as naked, but it depends on how closely you look at them. Both have hairs, but diagnostically you can differentiate them by zooming right in:
R. norvegicus - obvious hairs extend beyond edge of ear :
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R. rattus - fine hairs do not extend beyond edge of ear :
Most iNaturalist photos aren't really high enough resolution to detect this difference though.
All the above applies to adult rats, we really need a section dealing with the differences seen in juvenile rats. This is just a placeholder for that section!
Identification features such as head shape, ears, and eyes can be affected by being squashed in a trap, eg "large" eyes may simply be the result of the eyes bulging out as a result of head trauma.
Wet fur usually looks dark, so a wet Brown rat may well look black.
And remember "it is not necessarily a straight-forward task identifying what you have caught. The information provided can be fairly variable/vague and should be taken with a grain of salt. Every source says that an identification should be made based on the weight of identifying features, as it is rare to find a specimen matching every feature perfectly. " (🔗rat_id)