Brihat Parashara Hora Shastra
एवं संसाध्य चान्येषां हन्यात् स्वस्वपरायुषा । नृणां परायुषा भक्त्वा तेषामायुः स्फुटं भवेत् ॥ २३॥
Longevity for Other Living Beings. For other living beings as well such computations can be made. The said figure should be multiplied by the figure, corresponding to its full span of life and divided by the figure, corresponding to the full span of life for human beings.
english translation
evaM saMsAdhya cAnyeSAM hanyAt svasvaparAyuSA । nRNAM parAyuSA bhaktvA teSAmAyuH sphuTaM bhavet ॥ 23॥
hk transliteration by Sanscript