Responses of red-winged blackbirds, yellow-headed blackbirds and marsh wrens to glyphosate-induced alterations in cattail density

Published source details Linz G.M., Blixt D.C., Bergman D.L. & Bleier W.J. (1996) Responses of red-winged blackbirds, yellow-headed blackbirds and marsh wrens to glyphosate-induced alterations in cattail density. Journal of Field Ornithology, 67, 167-176.
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This study is summarised as evidence for the following.

	Action	Category
	Treat wetlands with herbicide Action Link
	Use herbicide to control problematic plants: freshwater marshes Action Link

Treat wetlands with herbicide

A controlled, replicated before-and-after study in 1990-1993 in 23 inland wetlands in North Dakota, USA (Linz et al. 1996), found that the densities of three songbird species were all significantly lower on sites sprayed with glyphosate, than on unsprayed sites (red-winged blackbirds Agelaius phoeniceus: 0.6 birds/ha on sites where 90% of the site was sprayed vs. 1.6 on controls; yellow-headed blackbirds Xanthocephalus xanthocephalus: average of 2.1 birds/ha on all treated sites vs. 3.1 on controls; marsh wrens Cistothorus palustris: 0.7 birds/ha on treated sites vs. 2.2). Experimental wetlands had significantly lower percentage covers of emergent vegetation. Sites were sprayed from the air with either 90%, 70% or 50% of the site treated. There were no differences between sites before herbicide application.
Use herbicide to control problematic plants: freshwater marshes

A replicated, randomized, controlled, before-and-after study in 1990–1993 of 23 freshwater marshes dominated by cattails Typha spp. in North Dakota, USA (Linz et al. 1996) found that marshes sprayed with herbicide had similar overall vegetation coverage to unsprayed marshes, but less live vegetation and more dead vegetation. After 1–2 years, coverage of emergent vegetation did not significantly differ between sprayed marshes (61–81% of marsh area) and unsprayed marshes (76–85% of marsh area). However, sprayed marshes had lower coverage of live vegetation (sprayed: 14–39%; unsprayed: 61–69%) including cattails (sprayed: 31%; unsprayed: 65%), and greater coverage of dead vegetation (sprayed: 25–58%; unsprayed: 15–16%). Before intervention, marshes destined for each treatment had statistically similar coverage of emergent vegetation (sprayed: 70–91%; unsprayed: 87%; data not reported for live, dead and cattail coverage). Methods: In July 1990 and 1991, glyphosate herbicide (Rodeo®) was sprayed on to a total of 16 cattail-dominated marshes (5.8 L/ha across 50–90% of each marsh). Seven similar marshes were left unsprayed. Emergent vegetation coverage was estimated from aerial photographs of each marsh, taken before (June 1990) and 1–2 years after (August 1991–1993) intervention. Some of the marshes in this study were also used in (2).

(Summarised by: Nigel Taylor)