The causes and consequences of coloniality in seabirds, and larids in particular, have received extensive study. Here, we use the Herring Gull (Larus argentatus) as a model organism to investigate the effect of nest density on chicks' growth rate and survival. On Appledore Island, Maine, Herring Gulls nest both in dense subcolonies and in more isolated situations, affording a unique opportunity for comparison of reproductive success of pairs nesting in both contexts on the same island. Chicks reared in dense subcolonies grew at a rate significantly higher than that of those reared in more isolated settings. Using mark-recapture analysis, we found that a chick's expected survival is dependent on hatch weight, hatch date, hatch order, and context (nest in dense or loose subcolony). The first chick to hatch in each nest had a significantly greater probability of surviving to fledging than the last-hatched chick. Last-hatched chicks had a significantly greater chance of survival from hatching to fledging if they were hatched and reared in the dense subcolony than in the loose subcolony. Further research is required to distinguish among the effects of parents' quality and age (and thus their ability to defend young and provide food), agonistic behavioral interactions, and proximity to nesting Great Black-backed Gulls (L. marinus, the main predator of Herring Gull chicks), on these differences. Our results suggest that pairs nesting in dense subcolonies benefit through chicks' greater growth rate and survival, possibly due to increased vigilance or greater access to food.