SPECIES

Purple Martin Progne subis Scientific name definitions

Charles R. Brown, Daniel A. Airola, and Scott Tarof
Version: 2.0 — Published September 10, 2021

Priorities for Future Research

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Introduction

A major research priority is to understand the causes of Purple Martin declines across much of the range (358, 276, 352). Studies are needed to understand demographic factors (productivity, recruitment, survivorship, and dispersal) that limit breeding populations (354). Although little attention has been given to potential limitations during migratory and overwintering periods, there is no evidence that birds from declining populations overwinter in different habitats than those from more stable populations, and thus habitat on the overwintering range may not be driving population declines (28).

A potential contributor to Purple Martin declines is increased use of neonicotinoid and other pesticides and the resulting reduction in insect prey populations (372, 361). Pesticides have been associated with declines in insectivorous bird populations in North America (373, 374, 375) and Europe (376), and declines in martin populations in California (92, 94). Most studies to date have been correlational and more study is needed on the relationships between localized levels of pesticide use, effects on flying insects, and resulting population effects on the Purple Martin. How the global decline in aerial insects (377) affects the Purple Martin independent of pesticide use also needs attention.

Potential effects of climate change on Purple Martin populations have not been studied in detail. Eastern Purple Martins did not accelerate migration and arrive earlier at breeding sites during a year of above average temperature (164), but showed plasticity in the timing of egg laying in response to temperature variation (378). Direct responses of the Purple Martin to climate change have not been documented, but are likely to be complex given variability in topography and climate across the species range in North America.

We need more information on migration routes and wintering areas of western and desert Purple Martin subspecies. Other priorities include study of the species' social behavior and its relationships within the genus Progne. Research designed to measure the costs and benefits of different colony sizes (in the style of 127) is needed. Such study would help reveal, for example, whether martin colonies form primarily because nest sites are limited (171, 267, 208), in order to facilitate extra-pair copulations (197, 222), or to provide protection from predators. Despite experimental plumage manipulations (207, 25), the advantages, if any, of the female-like plumage to yearling males are unclear, and additional work should investigate whether geographic differences exist in the extent of female mimicry (12) and, if so, why.

Instead of concentrating on explaining the female-like plumage of yearling males, perhaps we should ask why the Purple Martin and certain other Progne (but not all) are sexually dichromatic in the first place. Evolutionary and ecological relationships among the Progne martins are unclear. Members of this group are closely related and widely sympatric at certain times of the year, but little is known about the tropical species and how they interact with the Purple Martin during the overwintering period.

Recommended Citation

Brown, C. R., D. A. Airola, and S. Tarof (2021). Purple Martin (Progne subis), version 2.0. In Birds of the World (P. G. Rodewald, Editor). Cornell Lab of Ornithology, Ithaca, NY, USA. https://doi.org/10.2173/bow.purmar.02