I did not paste, Feenie. That's why I accidentally left off the d on 'heard'.
Thanks for pointing that out.
Heard her bird turn are random. There is no way of working out when to use 'ear, er, ur' or 'ir'. Children simply have to learn them for each word.
They can be grouped according to pattern and taught a few at a time, but in the end it's still a matter of knowing in which word to use which.
So here are all the common ones grouped by pattern:
^Berth, fern, her, herb, herd, jerk, nerve, perch, serve, stern, swerve, term, verb, verge, verse, were.
Longer words:
Advertisement, alert, anniversary, assert, certain, commercial, concern, confer, conserve, convert, deserve, dessert, detergent, determine, emerge, eternal, exert, external, fertile, germinate, hermit, impertinent, insert, interpret, jersey, kernel, merchant, mercury, mercy, observe, perfect, perfume, permanent, permit, person, pertinent, preserve, refer, reserve, reverse, sermon, serpent, terminate, termite, thermal, transfer, universal, university, verdict, vermin, version, versus, vertical.
Blur, burden, burglar, burgle, burly, burn, burr, burst, church, churn, curfew, curl, curlew, curse, curt, curve, disturb, excursion, fur, furnish, furry, further, gurgle, hurdle, hurl, hurt, hurtle, incursion, lurch, lurk, murder, murmur, nasturtium, nurse, nursery, occur, purchase, purple, purpose, purr, purse, return, slur, spur, spurn, spurt, sturdy, suburb, surf, surface, surge, surgeon, surgery, surname, surplus, survey, Thursday, topsy-turvy, turban, turbine, turf, turkey, turmoil, turn, turnip, turquoise, turtle, urban, urchin, urge, urn, yurt.
Birch, bird, birth, chirp, circle, circuit, circular, circumstances, circus, confirm, dirt, encircle, fir, firm, first, flirt, girder, girdle, girl, mirth, shirk, shirt, sir, skirmish, skirt, smirk, squirm, squirt, stir, swirl, third, thirst, thirteen, thirty, twirl, virtually, virtue, whirl, whirring.
Earl, early, earn, earnest, earth, heard, learn, pearl, rehearse, search, yearn.
Word, work, world, worm, worse, worship, worst, worth. Attorney.
Courtesy, journal, journey.^
Learning all of them takes many years.