The reproductive rates of yearling and older Ipswich Sparrows, Passerculus sandwichensis princeps

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Abstract
The mean reproductive rates (number of 7-day-old nestlings raised per year per individual) of yearling and older Ipswich Sparrows breeding on Sable Is., Nova Scotia in 1977 and 1978 were the following: yearling males 3.3, older males 4.2, yearling females 3.9, and older females 4.7. The mates of older males began nesting earlier, laid larger clutches, and renested more quickly after each brood than did the mates of yearling males, thereby laying slightly more clutches and significantly more eggs. Older females laid slightly more and slightly larger clutches than did yearling females, resulting in a significantly greater production of eggs. The number of nestlings aged 7 days (i.e., the age immediately before nest leaving) raised per egg laid varied only slightly with parental age. Consequently, the reproductive rate increased with age because parental abilities must have increased by the same proportion as did the production of eggs.