It is important to approach the birth indexes with as much information as possible from other sources. If the birth took place between 1864 and 1881 it may be possible to identify it from the FamilySearch birth register transcripts and then obtain the record image from IrishGenealogy.ie. If the area is known, but not the date, it may be useful to search the online 1901 and 1911 census returns to obtain at least an approximate age and hence date of birth. If the names of siblings and the order of their birth are known, but the area and date are not, it may be necessary to search a wide range of years in the indexes, noting all the names of the births that occur in the family, and then try to work out which births of the relevant names occur in the right order in the same registration district. If a baptism transcript exists on one of the church register sites, that will provide a precise time-frame. If the name is unusual enough, of course, none of this may be necessary. Rejoice if you have an ancestor called Horace Freke-Blood or Euphemia Thackaberry.