This strengthens the argument. It shows that a number of bird species benefit in the same way from herds of cattle, strengthening the argument that this benefit is why cattle egrets live around herds of cattle.

This does not affect the argument. Cattle egrets following other slow-moving animals does not make the author’s explanation for why they follow herds of cattle any less convincing. For all we know, buffalo and rhinoceroses also stir up insects that the birds consume.

This weakens the argument by offering an alternative explanation for the phenomenon. If living near cattle provides protection from potential predators, the egrets gain a significant safety benefit from their proximity to the herds.

This does not affect the argument. Cattle egrets’ propensity for living near slow-moving animals does nothing to weaken the author’s explanation for why they live around herds of cattle.

This does not affect the argument. The fact that forests are inhospitable to cattle egrets does not challenge the author’s explanation for why these birds live around herds of cattle.