Size is easily measured and Dominic Bird stretches the tape well beyond two metres and is nudging 118kg.

Coaches at the Chiefs can track his workrate from the GPS data chip in his jersey and team analysts provide an array of information about his lineout work, rucks hit, tackles made and accuracy at kickoffs.

What's more difficult to assess is the physical pressure players deliver, how much sting is in their tackles or cleanout, do they have a hammer tackle or a robust technique - the sort of detail which is another of the key areas in coaching and selection.

Chiefs coach Dave Rennie has noticed a change in Bird's work this season where he has added a layer of "brutality" to his work and become more of a presence in tandem with All Black Brodie Retallick.

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They are a formidable physical duo ready to rumble with any crew like the Bulls who bring serious second row size to Hamilton for tonight's Super Rugby contest, with Springbok lock Lood de Jager and RG Snyman parked in their pack.

Retallick is up with the best in the world where his high-revving engine, top quality skills and ruthless intent deliver strings of invaluable performances and those messages and uncompromising edge are filtering into Bird's work.

He played alongside some of the best when he was with the Crusaders but never managed a regular start as Sam Whitelock, Tom Donnelly and Luke Romano claimed most of the big matches before Scott Barrett and Jimmy Tupou began to make their run.

The All Black selectors liked the raw frame Bird offered and they called him up to join the end of year tour in 2013 where he got a start against Japan. A year later, he was called up as an injury replacement for Retallick and locked the scrum against Scotland.

Injury, a new wave of contenders such as James Broadhurst, Patrick Tuipulotu, then Barrett and a perceived lack of sting from Bird left him on the outer until the Chiefs called and together they recalibrated his playing brief.

Bird does not turn 26 until this week and many tight forwards have not found their style and settled into a rhythm at that age. Tuipulotu and Barrett may have skipped ahead in the national rankings but more of the work and attitude Bird is delivering at the Chiefs will add to questions at the All Black selectors' table.

A few snarls from Retallick and Rennie and some of the warrior spirit Liam Messam has shown as he reaches his 150th game tonight will be thrown into the recipe for Bird's resurgence. He has all the physical weapons and ultimately it all about how much he wants to succeed.