Who is responsible, the tenant or the landlod, to have stray animals removed from the property?

If the animals pose a safety or health risk then--

The landlord would be responsible if the tenants did not rent the entirety of the property; for example, it is a multi-unit dwelling, and the outside, hallways, etc. are common areas, and that's where the animals are found. When the tenants do not have exclusive control or possession, the landlord is responsible for common areas. (Note: if the animals are not a health or safety risk, the landlord does not need to do anything; the landlord is only obligated to address issues affecting health, safety, or ability to use the property.)

However, if the tenants did rent the entirety of the property, including the outdoor space (e.g. it is a single family home; the tenants rented the entire property), the tenants would have to remove any animals they considered undesirable or hazardous, unless the landlord in some way caused or contributed to the animals being there; that's because if the tenants have sole possession over the property, they are the ones who control and have the right to allow or remove animals.