The developmental period is a critical phase in birds, influencing even lifetime reproductive success. The gut microbiome (GM) is important herein, affecting digestive capacity and immune function. Diet impacts the GM, but wild nestlings may experience resource limitations, which may also affect the GM. We investigated the effects of a week of food restriction early in life on the GM in captive rock pigeon nestlings (). We sampled the GM at 0, 2, 4, 7, 8, 12, 20, 27, and 38 days and in foster parents. Alpha diversity varied only with age. However, differences in alpha diversity between nestlings and adults were larger during food restriction. Beta diversity varied with age, food treatment, and their interaction term. Four of the eleven major genera varied with age, while four others did not vary with age or food treatment. Major genera that contained potential pathogens (- and ) were more abundant under food restriction. Food restriction thus affected GM development. The increase in alpha diversity and potential pathogens suggest that suppressed immune function may mediate the impact of food restriction on the GM. The effect diminished when food restriction was ended, suggesting that in wild nestlings, the impact of food restriction on the GM may be short-term.