( ( These birds ) ( ( have ( ( featherless neck ) ( which ( ( the naturalists ) ( believe ( that ( it ( ( plays ( ( a ( pivotal role ) ) ( in thermoregulation ) ) ) ( -LRB- ( ( maintaining ( adequate ( body temperature ) ) ) -RRB- ) ) ) ) ) ) ) ) ) ) . ) )
(ROOT (S (NP (DT These) (NNS birds)) (VP (VBP have) (NP (NP (JJ featherless) (NN neck)) (SBAR (WHNP (WDT which)) (S (NP (DT the) (NNS naturalists)) (VP (VBP believe) (SBAR (IN that) (S (NP (PRP it)) (VP (VBZ plays) (NP (NP (DT a) (JJ pivotal) (NN role)) (PP (IN in) (NP (NN thermoregulation)))) (PRN (-LRB- -LRB-) (S (VP (VBG maintaining) (NP (JJ adequate) (NN body) (NN temperature)))) (-RRB- -RRB-)))))))))) (. .)))
These birds have featherless neck which the naturalists believe that it plays a pivotal role in thermoregulation (maintaining adequate body temperature).
(ROOT (S (NP (NNP Thermoregulation)) (VP (VBZ is) (NP (NP (DT the) (NN process)) (SBAR (WHNP (WHADVP (WRB when)) (NNS animals)) (S (VP (VBP maintain) (NP (DT an) (JJ internal) (NN temperature))))))) (. .)))