Three migrant birds, three migrant birds, see how they change

This week I investigated three migratory song bird species to see how things were changing on a smaller scale, and while I chose these species largely because I love their plumage (I’ll admit to being shallow here and not considering the “inner-bird”), I also selected them because they represent three different scenarios: a complicated situation, a real worry, and a success story. And I have no doubt that people will have a range of attitudes toward these species depending on where they are and how they use the land around them.

Bobolink, Male, May, PA

The complicated history of Bobolinks- Bobolinks (Dolichonyx oryzivorus) represent an interesting scenario that forces us to consider our responsibilities for preserving species whose ranges we helped expand. Bobolinks are grassland birds who nest on the ground. They have a fondness for pastures and hay fields, and their tendency to consume rice during migration led McAtee (1919) to call them “the most exasperating bird pest of the United States (431).” (What do you suppose was the second most-exasperating?)  Bobolinks are considered ‘Least Concern’ by the IUCN, an international group founded in 1948 to assess environmental issues and promote conservation action (I highly recommend a look at the IUCN Red List site where you can get status reports for species that interest you). Across central and eastern North America, however, consistent declines in the bobolink population have been recorded over the past few decades. Here in NH, the trend is a 2.6% decline per year (visit NH Fish and Game’s “State of the Birds” report for info on many species), in Wisconsin the average is a bit less than 2% per year according to the Wisconsin Bird Conservation Initiative, and the overall trend according to data from the Breeding Bird Survey is a 1.6% decline per year between 1966 and 1996 (Peterjohn & Sauer 1999). Part of this decline is connected to the changes in land use over the past century: as farmland is converted by development or abandoned to revert back to forest, breeding habitat is lost. Wintering habitat in South America is also being lost- according to Di Giacomo et al. (2005), the birds’ winter range has decreased by 25%; in Argentina, for example, 90% of the original grasslands have been lost to development and agriculture. Another issue facing bobolinks in their breeding grounds is earlier and more frequent harvests of hay fields- farmers now cut hay 2-3 times per summer and the first cutting is 2-3 weeks earlier than it was 70 years ago (The Bobolink Project- see below). Earlier cutting during the nesting season exposes nests to predators and can also flush chicks out of nests before they are ready. Why is this a complicated issue? Well, the general feeling is that bobolink populations increased in eastern North America as a result of human, specifically European colonist, clearing of the land for farming (although there is some debate on this- see Askins 1999). Now that much of that land is unsuitable for breeding habitat, the bobolink population is declining- so there is the question of whether this really represents a problem for the species and whether we should take action to stabilize and support these populations if their expansion was the result of our previous actions. I’m not sure where I fall in this debate in general- I have issues with human encouragement of exotic species, but I’m still figuring out how I feel about the idea of range expansion of native species. If that expansion came at the cost of another native species, that doesn’t seem right to me, but, if we caused the bobolink to become common here in the first place, don’t we have a responsibility to keep it here? While I’m still formulating my own opinions on this matter, others have taken action- the bobolink was declared threatened in New Jersey in 1979 and there are programs to conserve and recover grasslands in that state for bobolinks and other ground-nesting grassland species. The University of Connecticut and the University of Vermont have partnered for The Bobolink Project (which started at the University of Rhode Island in 2007), a program in which community members pay farmers to delay haying and use different farming practices for the benefit of bobolinks and other species.

Golden Winged Warbler

Rough times for Golden-winged Warblers- I have never seen a golden-winged warbler (Vermivora chrysoptera), unlike the other two species in this post, and with good reason: they are only occasionally found in NH, and their numbers are decreasing. They are considered ‘Near Threatened’ by the IUCN and are a Federal Species of Special Concern in the US. The immediate cause for those rankings is clear- the Golden-Winged Warbler Atlas Project estimates a 7.6% decline per year (wow!) for the northeast population, although numbers are increasing in northern and western areas. It is not definite, however, why this species is declining while blue-winged warblers are increasing. Golden-winged warblers like to nest in early successional habitat, meaning that they like abandoned farmland that is starting to get shrubby and swamps with alder thickets- when the forest starts to fill in too much, the birds move on. There is concern over loss of breeding habitat, but this doesn’t seem like a complete answer- in the state of New York, as woody vegetation in golden-winged warbler habitat increased, the birds declined, but at a faster rate than the reforestation (Confer & Knapp 1981). The golden-winged warbler decline has happened in tandem with an expansion in the range and numbers of the blue-winged warbler, and there are theories about blue-winged warblers out-competing golden-winged warblers through more aggressive behavior or greater avoidance of nest parasitism by cowbirds, but neither effect was found by Confer & Larkin (1998) and Coker & Confer (1989), respectively. If we can’t say exactly what is happening to the population, it becomes more challenging to reverse a downward trend, so a lot of the focus, for example with the Atlas Project mentioned above, is on gathering information. At the moment, it is difficult to predict what will happen to the species in the long run.




Bluebird House

There’s no place like home for eastern bluebirds- I like the idea of including information on conservation efforts that are having a positive impact, and the eastern bluebird (Sialia sialis) is a definite ray of sunshine in that respect. These birds are secondary cavity nesters- they can’t create their own nest holes, but they will use cavities created by woodpeckers and other animals (including us); they also like open habitats. As land was cleared for farming, eastern bluebird populations responded, getting an extra boost from the nest sites provided by wooden fence posts used along field edges. Between 1920 and 1970, however, things took a downward turn: wooden posts were replaced by metal ones, pastures and field borders were cleared to increase planted fields, and competition for nesting cavities with European starlings and house sparrows, two introduced species, limited nest options. Fortunately, bluebirds have a lot of friends who are willing to provide nesting boxes. With boxes manufactured to the correct specifications and then monitored for use by exotics, bluebirds made a comeback. Today in NH they are increasing, and the National Audubon Society considers their recovery across their range a true success story. Eastern bluebirds are so charismatic that a number of states, such as Maryland, have bluebird societies dedicated to their conservation- just imagine if every bird in trouble had that kind of support!

Bobolinks, golden-winged warblers, and eastern bluebirds represent three different scenarios for song birds: a) we know the population is decreasing and we know some of the reasons for it, but we’re not sure how serious it is given our historical impact; b) we’re worried about the big declines we’re seeing in some areas, but we’re not quite sure exactly what’s happening and how to counter it; and c) we saw the decline, acted to support the species, and our efforts are making a difference. Maybe you can think of a bird in your area facing one of these scenarios, or maybe you’re not quite sure what the bird community in your backyard is experiencing- next week I’ll be looking at ways you can get better informed about or even directly involved in bird conservation, so that, even if you don’t like bobolinks because they eat rice and sprouted wheat, or don’t have golden-winged warblers in your area, or have no place to put up a bluebird nesting box, you can still get in the game.

Works cited:

Askins, R.A. 1999. History of grassland birds in eastern North America. Studies in Avian Biology 19: 60-71.

Coker, D.R. and J.L. Confer. 1989. Brown-headed cowbird parasitism on golden-winged and blue-winged warblers. The Wilson Bulletin 102(3): 550-552.

Confer, J.L. and K. Knapp. 1981. Golden-winged warblers and blue-winged warblers: the relative success of a habitat specialist and a generalist. The Auk 98: 108-114.

Confer, J.L. and J.L. Larkin. 1998. Behavioral interactions between golden-winged and blue-winged warblers. The Auk 115(1): 209-214.

Di Giacomo, A.S., A.G. Di Giacomo, and J.R. Contreras. 2005. Status and conservation of the bobolink (Dolichonyx oryzivorus) in Argentina. USDA Forest Service Gen. Tech. Rep. PSW-GTR-191: 519-524.

McAtee, W.L. 1919. Observations on the shifting range, migration, and economic value of the bobolink. The Auk 36(3): 430-431.

Peterjohn, B.G. and J.R. Sauer. 1999. Population status of North American grassland birds from the North American Breeding Bird Survey. Studies in Avian Biology 19: 27-44.