Date of Award

Fall 2024

Project Type

Thesis

Program or Major

Natural Resources

Degree Name

Master of Science

First Advisor

Adrienne Kovach

Second Advisor

Jeff Garnas

Third Advisor

Chris Elphick

Abstract

The Saltmarsh Sparrow (Ammospiza caudacuta) is a non-territorial, multiply mating passerine with an uncommon polygynandrous mating system in which females are reproductively available with primarily synchronous timing during 3 breeding cycles within the breeding season. In similarly multiply mating species with synchronously available females, home range size and time within breeding season have been identified as drivers of male reproductive success; however, these are atypical characteristics of success in avian mating systems. We investigated the relationship between male Saltmarsh Sparrow home range size, location, age, time within breeding season, and male reproductive success. We performed nest monitoring, mist netting, and collection of genetic samples from banded individuals at two marshes in Maine and New Hampshire, in the northern part of the species range. We also conducted resighting surveys of color-banded individuals to assess the home range sizes and locations of breeding males at each site. We used single nucleotide polymorphisms (SNPs) identified from restriction-site associated DNA sequencing (RAD-seq) to conduct paternity analysis of 421 nestlings and unhatched eggs from 190 Saltmarsh and Nelson’s sparrow nests over the course of two breeding seasons. We found no significant relationship between male home range size or search effort and total offspring produced per male. We also found no difference in annual number of offspring produced by older (Year 2+) males compared to younger (Year 1) males. We did find differences in the timing of reproductive effort among older and younger males. Specifically, we found that Year 2+ males as a group produced significantly more offspring during the first cycle in the breeding season than Year 1 males, and that older males remained reproductively active longer during the breeding season than Year 1 males. The lack of influence of home range size on male Saltmarsh Sparrow reproductive success, as well as the observed concentration of male home ranges around areas where females nest in high densities, indicate that Saltmarsh Sparrows may use endurance rivalry as a tactic for increasing male reproductive success in addition to scramble-competition mate-searching strategies. This idea is further supported by the extended period of reproductive activity observed in Year 2+ males compared to Year 1 males.

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