Altricial nestlings hatch at an early stage of development, and depend on their parents to feed them. The quality of the parental care is of great significance to the nestlings fitness and future survival. In the early stage of life, differently sized nestlings are likely to have different abilities to swallow prey. This experiment was designed to test for whether differently sized nestlings have different swallowing abilities, and if so, whether parents adjust prey size according to the size of the nestling they feed. In addition, the male and female feeding patterns were studied with respect to prey size and choice of nestling. This was done by heterospecific cross-fostering experiments, with nestlings from two species of tits (great tit Parus major and blue tit Cyanistes caeruleus). Parent great tits were recorded when caring for nestlings only two days old in broods of three different compositions (n = 26); (1) all nestlings were great tits, (2) all nestlings were blue tits, and (3) one nestling was great tit the rest were blue tits. The smaller blue tit nestlings displayed significantly longer swallow times than the great tit nestlings, and strongly indicated that smaller nestlings have greater difficulties swallowing than larger nestlings. This agrees with previous work on nestling birds. However, the great tit parents did not seem to accommodate the different swallowing ability of the blue tit and great tit nestlings. They did not deliver smaller prey volumes to smaller nestlings, which is inconsistent with the commonly observed trend of prey size to increase with nestling age. The findings though were slightly ambiguous, as the two smallest nestlings within a brood seemed to be fed adjusted prey. However the trend point toward no prey size adjustment to nestlings size in the great tit, and the results indicate that parents do not adjust equally well to differences within a brood as they do to the changes in the needs of a brood over the nestling period. The male and female choice of nestling did not differ, and both selectively fed the larger great tit nestling in the mixed broods. Still, the female seemed to adapt her care better to the smaller nestlings than the male, as she delivered smaller sized prey. The same pattern was not detected within treatments and the female actually had a tendency to deliver larger prey than the male to the nestlings in the great tit group.