( they ( ( ( use ( their ( own ( metabolic heat ) ) ) ) ( to ( maintain ( ( ( a ( warm ( , ( constant ( body temperature ) ) ) ) ) , ) ( aided ( by ( insulation ( provided ( by ( ( feathers and ) ( ( a layer ) ( of fat ) ) ) ) ) ) ) ) ) ) ) ) . ) )
(ROOT (S (NP (PRP they)) (VP (VBP use) (NP (PRP$ their) (JJ own) (JJ metabolic) (NN heat)) (S (VP (TO to) (VP (VB maintain) (NP (NP (DT a) (JJ warm) (, ,) (JJ constant) (NN body) (NN temperature)) (, ,) (VP (VBN aided) (PP (IN by) (NP (NP (NN insulation)) (VP (VBN provided) (PP (IN by) (NP (NP (NNS feathers)) (CC and) (NP (NP (DT a) (NN layer)) (PP (IN of) (NP (NN fat))))))))))))))) (. .)))
they use their own metabolic heat to maintain a warm, constant body temperature, aided by insulation provided by feathers and a layer of fat.
(ROOT (S (NP (NNP Metabolism)) (VP (VBZ produces) (NP (NN waste) (NN energy)) (PP (IN in) (NP (NP (DT the) (NN form)) (PP (IN of) (NP (NP (NN heat)) (, ,) (SBAR (WHNP (WDT which)) (S (VP (VBZ helps) (S (NP (JJ warm-blooded) (PRN (-LRB- -LRB-) (NP (NNP endotherm)) (-RRB- -RRB-)) (NNS animals)) (VP (VB conserve) (CC and) (VB maintain) (NP (NN heat)) (PP (IN at) (NP (DT a) (ADJP (RB relatively) (JJ constant)) (NN body) (NN temperature))))))))))))) (. .)))