In the breeding female tree swallow, humoral immunocompetence (HIC) is inversely correlated with laying date. This means that, on average, a bird that lays its eggs earlier has a stronger antibiotic response to an antigen than a bird that lays later. A tree swallow that is handicapped by wing-clipping generally has a lower HIC. These relationships could be interpreted as supporting the conclusion that a female that lays earlier acquires a higher HIC, but the authors of the study that found the correlations believed this unlikely, due to the colder temperatures near the start of the breeding season. Instead, they thought that HIC could be a measure of quality, and that a higher quality female is able to lay earlier. The authors also postulated that it is an indicator of workload, as shown by the lower HIC of handicapped birds.