Did not find anything on the Mckerras surname at ancestry or at surnamedb.com . Surnamedb.com had something on Falconer surname:
This interesting surname has two distinct possible sources, the first and most likely being from an Old French occupational name for a keeper or trainer of hawks. The derivation is from the Old French "fau(l)connier", "one who hunts with falcons or follows hawking as a sport", also, "keeper and trainer of hawks". The hawk trainer was held in high esteem in medieval times as it was his responsibility to supply hunting hawks to his overlord or the lord of the manor. Early examples of the surname include: Henry le fauconer (Yorkshire, 1219), and John Fauconner (Somerset, 1327). The name may also be occupational for one who worked a "faucon", that is, a type of medieval crane or windlass. In 1282 the "faukonarii" or "falconarii" at Caernarvon Castle were paid 6d. per day in summer and 5d. in winter for operating this device. One of the earliest namebearer to enter America was Thomas Faulkner, aged 28 yrs., who appears on a "List of The Living in Virginia" on February 16th 1623, having come over on the "Mary Providence" in 1622. A Coat of Arms granted to the Falconer family of Sloane Street, Chelsea, is a paly of six black and silver, Overall a bend vert, thereon three trefoils in gold. A dragon's head and neck, wings addorsed, couped at the shoulders proper is on the Crest. The first recorded spelling of the family name is shown to be that of Henry Falkenar, which was dated 1194, in the "Curia Regis Rolls of Wiltshire", during the reign of King Richard 1, known as "Richard the Lionheart", 1189 - 1199. Surnames became necessary when governments introduced personal taxation. In England this was known as Poll Tax. Throughout the centuries, surnames in every country have continued to "develop" often leading to astonishing variants of the original spelling.
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