During the 1970s and 1980s, the vast majority of international child abductions were undertaken by the non-custodial parent after a divorce. Of course this was naturally the case because the custodial parent legally had the right to remove children overseas, while the non-custodial parent did not. In many of these cases, the abducting parent was the father. Mothers were generally granted custody and fathers would abduct their children overseas in reaction to this. In fact, at the time the Hague Convention was being put into place, the typical case was of a father who was so frustrated about the mother being granted sole custody of the children that he would abduct them overseas.
Similarly, many abductions carried out during that time period were just prior to a divorce becoming final. In many of these cases it is likely that the parent who was about to lose custody chose to abduct the children overseas instead. As above, many of the abducting parents in these cases were fathers who were less likely to obtain custody over their children. Some studies at the time indicated that as many as 70% or more of the international child abductions were carried out by men (studies by Agopian and Janvier et al.).
Recently, these trends have begun to reverse. Several more recent studies have put the number of male abductions at closer to 50% (Greif and Hegar and Johnston et al.). Figures from the US State Department estimate that as many as 63% of abductors in Hague cases are women. US case law also has shown an increase in abductions by mothers with only 33% of recent cases involving fathers abducting their children. Similar statistics from Scotland and England also indicate that the trend in abductions may be leaning further toward mothers rather than fathers.
Whether this change is due to the implementation of the Hague Convention or simply changes in society and custody norms is difficult to tell. It is also unclear whether this current trend will continue into the future or reverse itself once again.