I am carrying out a One-Name Study of the name Bertie worldwide, and am keen to hear from anyone with this name in their families and will try to help provide information. I can probably provide many short-cuts to your research from data already collected. Most individuals alive in the 19th century and many from the 20th, have been assembled into extensive pedigrees. In some cases, may be able to assist and do some extra research on your behalf. I would also welcome offers of assistance with research!
As you would expect with a Guild-registered study, this is a true One-Name Study - therefore am interested in any Bertie anywhere in the world and irrespective of whether they relate to my own Bertie line (which in fact started out as Berty).

I systematically collect data on the variants, however, many other 'deviant' spellings can be found throughout history, which may be caused by hearing or transcription errors, but at this time it has not been determined which is a variant, deviant or a name on it’s own merit.
An important consideration when searching censuses is the possibility of enumeration and transcription errors. The following 'names' have been found:
Bairtie, Bairty, Baitie, Barty, Bearty, Bertee, Berti, Bertin, Berttey, Berty, Bertye, Birtie, Birty, Burtie, McBertie and von Bertie.

Whilst at present I do not have the exact origin of the surname, there are suggestions that the name may have descended from the Saxons.
According to the book “Five Generation of a Loyal House” by Lady Georgina Bertie (Georgina Anne Emily Kerr (1806-1881)) there is reference to a Leopold de Bertie who was Constable od Dover Castle in the reign of King Elthered the Unready (978–1013 and 1014–1016)
A very pretty tradition brings the Berties, at the time of the Saxon invasion, from Bertiland, in Prussia, to Bertiestad, now Bersted, in Kent, where "one of our Saxon monarchs gave him a castle and town I" A Cottonian MS. makes one Leopold de Bertie (I) constable of Dover Castle in the time of King Ethelred, but his son of the same name, being out of favour at court, retired to France. From that country in the year 1154 his descendant came to England with Henry II., who restored to him his ancestral estate at Bersted. See Burke's Ext. Peerage.
— Patronymica Britannica, written: 1838-1860 by Mark Antony Lower

There is also a Scottish line possibly goes back to 946 A.D. but has not been linked into the English line (information courtesy of Evelyn Radford nee Bertie)

There are titles in the British Peerage,

• Earl of Abingdon
• Baron Norreys of Rycote
• Earl of Lindsay
• Baron Willoughby de Eresby
• Viscount Thame (Extinct)
• Earl of Berkshire (Extinct)

The following is a list of the countries where the name has been identified as having being present

Argentina, Australia, Belgium, Brazil, British Virgin Islands, Canada, Chile, China, Egypt, England, France, Guyana, India, Indonesia, Ireland, Italy, Ivory Coast, Kenya, Malaysia, Netherlands, New Zealand, Northern Ireland, Peru, Saint Kitts & Nevis, Scotland, South Africa, Spain, Switzerland, Trinidad & Tobago, United States, Venezuela, Wales. 

I have now commenced a DNA study for the name Bertie

Details can be found here