Does reproductive performance improve with age in female European starlings, Sturnus vulgaris?

Abstract

Studies have shown that the most energetically costly event in a bird’s life cycle is that of breeding, particularly for females who lay nutrient-rich eggs. Studies also show that older males and females are often preferred as mates. Potential reasons include older individuals having experience with locating good feeding sites, and provisioning offspring, as well as being in better condition or possessing superior genes. European Starlings (Sturnus vulgaris) are cavity-nesting passerines with bi-parental care, and have hackles whose length of iridescence allows classification of adults into one of two age categories (Second year, SY, who are breeding for the first time; After Second Year, ASY, who likely bred at least once before). The objective of my study was to determine if older females had higher reproductive performance than younger females, using four years of data. I predicted that ASY females would be in better condition than SY females, and that they would have larger clutch sizes, a higher mean egg mass, and greater hatching and fledging success. In support of my predictions, ASY females were in significantly better condition than SY females, and had larger clutch sizes. ASY females also tended to have higher fledging success, although mean egg mass and hatching success did not differ between ASY and SY females. Condition and reproductive performance in this population of European Starlings were higher for older females than first-time breeding females, suggesting that these older females might be expected to be preferred as mates.