Although much work has been done on the breeding biology of the species, a number of key areas remain in need of investigation. These include:
- Aspects of the mating system need to be better understood, and this should be a high priority given the species’ unusual breeding biology (134). Further work, perhaps including the use of captive birds, should include obtaining a better understanding of sexual signaling (including the development of song and other vocalizations in young birds, cultural inheritance, and hybrid song); mate competition; female choice; sperm competition; and the use of sperm lavage to determine conditions for sperm transfer during male mounting. Additionally, we know little about the effects of age and experience on breeding behavior and mating success.
- Although, we have learned a lot about the hybrid zone with Nelson’s Sparrow, many questions remain about the circumstances under which individuals will hybridize, and the consequences for behavior, song, breeding success, and population dynamics.
- Related to better describing breeding biology, is the question of why Saltmarsh Sparrow has evolved the mating system that it has, and why it differs from close relatives.
- Further work is also needed on the precise reasons for specific nest site selection decisions, in particular, sorting out environmental factors related to security against predation or flooding versus inexperienced breeders making poor choices (191). There is also variation in nest placement relative to vegetation characteristics across sites that is not well understood (186; K. Ruskin et al., unpublished data).
- Although, second broods are widespread across the species range, we lack good information on their frequency and its implications for population dynamics.
Research on the species' life-history has increased in recent years, but a number of topics remain poorly known:
- Detailed quantitative information on fledgling dispersal and adult female provisioning behavior during post-fledging period, time to independence, and time to initiation of second brood nests after first brood fledges will contribute to better estimates of post-fledging juvenile survival and annual fecundity/female.
- Incomplete information on juvenile and adult survival, and variation in sex ratios contribute most to uncertainty over extinction risk (188). Adult survival estimates are now available over large geographic areas, but all are based on short time series and a better understanding of temporal variation is needed. Survival and movements of young birds post-fledging is poorly understood.
- Better information on dispersal between populations, recruitment rates into breeding populations, and population differentiation, also would be helpful, and could be especially important as suitable habitat declines and becomes increasingly fragmented.
- Information on migratory timing and pathways is beginning to emerge via ongoing telemetry studies, but much about stopover ecology remains unknown, in particular whether there are certain sites that are especially important. Since most mortality appears to occur during migration (202), this information could have important conservation implications.
- There are no comprehensive surveys of the overwintering grounds or detailed information about winter habitat selection. As a result, little is known about responses to management actions (e.g., marsh burning) at non-breeding sites, and we lack the data to identify priority overwintering sites. Better information on winter site fidelity and connectivity between breeding and nonbreeding sites also would be useful.
Given growing evidence that Saltmarsh Sparrow is declining and faces a high risk of extinction, a number of conservation-related topics have become high priorities for investigation. These include:
- Regular monitoring of Saltmarsh Sparrow numbers at key marshes used in prior range-wide studies, to better track population trends.
- Experimental work on the effectiveness of habitat management, including (a) the use of sediment additions to maintain marsh elevation, (b) tidal flow manipulations, and (c) facilitated marsh migration designed to create new marsh.
- Exploration of the methods required for successful captive breeding perhaps should also be explored before the population gets too small.