CLICK HERE FOR THOUSANDS OF FREE BLOGGER TEMPLATES »

Tuesday, April 10, 2012

Thesis Proposal

I'm sitting at my computer, pretending to be productive, supposed to be working on the methods for my thesis. Instead, I think I will post my proposal here. That's kind of productive. Creating a study and methodology that will allow for strong statistical analysis BEFORE doing the study has created a great deal of work over the last two weeks (work I thought was finished). One of my committee members has been a great deal of help.


Changes in Singing Behavior in Response to Playback in House Wrens (Troglodytes aedon) and Bewick’s Wrens (Thryomanes bewickii)

By Teresa O. Wicks

Introduction

Birds, Bird Song and Current Research

Bird song, often in conjunction with other factors, provides birds with a way to communicate their reproductive status, territorial boundaries and fitness. In some species, bird song also demonstrates a male’s position as either a dominant or submissive male. In several species bird song also indicates suitable breeding habitat, with males making decisions about where to nest based on conspecific (same species) singing and nesting. Ward and Schlossberg (2004) found that playback effectively attracted black-capped vireos (Vireo atricapilla) to ideal woodland habitat in Texas where one or no pairs of vireos nested in previous years. The study also found that male vireos drawn to the area initially countersang with the playback but eventually habituated. Vireo nests in the study areas were also more successful than nests in similar control areas.

Male singing can encourage breeding behavior in females of the same species. Mota and Depraz (2004) found that female Serins (Serinus serinus) exposed to playback of male Serin songs, during the nest-building stage of the breeding season, spend more time nest building than females not exposed to additional songs. Females of many species prefer males that have a large song repertoire, win male-male singing “contests” or that sing aggressively. For example, Reid et al. (2004) found a strong correlation between song repertoire size and nesting success in Song Sparrows (Melospiza melodia). Mennill et al. (2002) found that playback at the start of the breeding season caused females mated to high ranking male Black-capped Chickadees (Poecile atricapillus) to engage in extra-pair mating with increased frequency. Females mated to low-ranking male Black-capped Chickadees did not engage in increased extra-pair mating. This is the result of females eavesdropping on male-male singing competitions and making judgments about fitness based on males “winning” or “losing” singing competitions. Female Great Tits (Parus major) also make decisions about extra-pair matings by eavesdropping on male-male singing competitions (Otter et al. 1999).

Males that sing aggressively typically do so in defense of their territory and aggressive/defensive singing is a sign of a male’s fitness. In European Robins (Erithacus rubecula), males sing aggressively in response to conspecific singing overlap (Dabelsteen et al. 1997) while male Corn Buntings (Miliaria calandra) sing aggressively in response to alternating conspecific singing (Osiejuk, Ratynska and Cygan 2007). Hyman (2007) found that Carolina Wrens (Thryothorus ludovicianus) countersing as a sign of aggression, but only in response to the songs of foreign male Carolina Wrens. Stoddard et al. (1991) found that song sparrows respond more to stranger song and neighbor song at the opposite boundary from where they were normally found than to their neighbors. Molles and Vehrencamp (2001) found that banded wrens (Thryothorus pleurostictus) were able to recognize neighbor songs from stranger songs, even if the strangers were singing a shared song. Contrary to these findings, Wiley (2005) found that Acadian Flycatchers (Empidonax virescens) showed only marginal recognition of neighbors compared to strangers songs, and only after 30 minutes of song playback. This is likely because there is very little song variation from individual to individual in Acadian Flycatchers.

There are a number of factors involved in how behavior changes in response to playback. First, is the geographic location songs being tested came from. As mentioned above, males respond less to songs from their neighbors than they do from strangers. Second, location songs are played from. A male will respond more aggressively to a neighbor’s song played within their territory or along the opposite boundary. Third, is the duration of the playback. In Wiley’s (2005) study of Acadian Flycatchers, a slight recognition response was recorded after 30 min of playback but not after only two minutes. Finally, the time of day and season of playback can influence behavioral changes in response to playback. Erne and Amrhein (2008) found that Winter Wrens (Troglodytes troglodytes) increased the number of songs sung during the pre-dawn chorus following simulated territory intrusion at sunset the previous day. Little research has been done into response as a factor of migratory status (residential vs. migratory).

Purpose/Background

The purpose of this study is to investigate changes in singing behavior, in response to playback of non-neighbor conspecific song, in Bewicks’ Wrens (Thryomanes bewickii) and House Wrens (Troglodytes aedon). Bewick’s Wrens are a non-migratory species of wren, which maintain territories year-round. Territory size is an average of 4.9 acres in dense riparian woodlands and an average of 9.4 acres in open woodlands (Kroodsma 1973). These birds know their neighbors and will sing (at a greatly reduced level) even in the winter, to defend their territory. House Wrens are a migratory species of wren and do not maintain a territory year-round. House Wrens will return to their breeding territory from previous years, or if that territory is occupied, find one adjacent to their previous territory. House Wren territories are an average of 2.3 acres (Kroodsma 1973). Given their migratory life history, males do not know their conspecific neighbors as well as the residential Bewick’s Wren.

Hypothesis

Hypothesis A is that Bewick’s Wrens will display a greater change in singing behavior, in response to playback, than House Wrens. Bewick’s wrens will sing more songs per minute, sing earlier in response to playback and will approach the speakers closer and for longer than House Wrens. These behaviors are associated with aggressive territorial defense, which Bewick’s Wrens will exhibit more strongly because of their year-round territory defense. Alternatively, hypothesis B is that House Wrens will display a greater change in singing behavior, in response to playback, than Bewick’s Wrens. As a migratory species, House Wrens have a much shorter time on their breeding grounds than Bewick’s Wrens. Because of this, House Wrens will display the changes in singing behavior associated with territory defense mentioned above. The null hypothesis is that changes in singing behavior in response to playback will be the same in both House Wrens and Bewick’s Wrens.

Implications

Changes in singing behavior can have serious implications for nesting success for individual males within a population. Birds that sing to defend their territory could lose territory if neighboring males see them as weak (in response to “loosing” to the playback). In species where females make extra-pair mating decisions based on a males rank or ability to out sing other males in competitions, males can lose paternity in their nests. Finally, a male that is viewed as weak by its neighbors and/or female conspecifics may not find a mate for that year, missing out on the opportunity to pass on his genetics.

Birders and Playback

The territorial and hierarchical behaviors displayed by most songbirds are what make playback a successful tool for birdwatchers wanting to attract rare or hard to find birds. According to Cordell and Herbert (2002), birding is the fastest growing recreational activity, growing 232% from 1983 to 2001. Birdwatching, though less damaging than many forms of recreation, can have a negative impact on breeding, nesting success, abundance and diversity. Though very little research has been done on the effects of birders using playback, anecdotal accounts abound. Birding organizations, such as the Americans Birders Association (2011), recommend limiting the use of recordings and other methods of attracting birds. Using playback to attract birds listed as threatened or endangered is interpreted as harassment and is therefore a violation of the Endangered Species Act of 1973. The use of playback is also illegal in many parks and refuges.

Cutright (1999) recounts the story of a Fan-tailed Warbler (Euthlypis lachrymose) and Elegant Trogons (Trogon elegans) in Arizona. The Fan-tailed Warbler is a rare bird and within only a few days, enthusiastic birders, armed with playback and the desire to add another bird to their life lists, had apparently pressured the bird into moving out of the area. Elegant Trogon sightings are declining every year in southeastern Arizona, potentially due to disturbances of their nest sites by birders and photographers.

While many birders, birding organizations and researchers recommend using playback sparingly, there are some studies and anecdotal evidence that playback can be positive for birds. Some arguments in support of playback claims birds that use song to delineate territory are unaffected by playback and that playback can help stimulate breeding behavior in these species. Anecdotal evidence shows that playback may give a territorial male a feeling of satisfaction at having “scared off” a competitor when the playback ends and birders have moved on.

David Sibley (2011) gives an in-depth discussion of the arguments for and against using playback and provides guidelines for birders to help reduce the negative impacts of playback. Ultimately, well-designed, long-term studies on the impacts of playback on birds need to be conducted to properly inform birders of how and when to use playback (Sekercioglu, 2002).

Methods

Study area and subjects

In this study, I will look at changes in singing behavior in response to playback House Wrens and Bewick’s Wrens. Bewick’s Wrens are year-round residents throughout their western range (British Columbia to Mexico), found in scrub or thickets in open areas, open riparian forests and chaparral (Kennedy and White 1997). Similar to other wrens, Bewick’s Wrens learn their song in the winter before their first breeding season, from the males in neighboring territories, rather than from their fathers (Kroodsma 2005). House Wrens are migratory wrens, found in open forests, along forest edges and in meadows with sparse grass, trees or thickets (Kroodsma 1973).

I will locate thirty Bewick’s Wren and thirty House Wren territories, in sites in both Josephine and Jackson Counties. Josephine County sites include Whitehorse Park and Fish Hatchery Park. Jackson County sites include Whetstone Savannah, Emmigrant Lake, Upper and Lower Table Rocks, Valley of the Rogue State Park and sites along the Bear Creek Greenway.

Test Songs

As territories are discovered, songs of the males in each territory will be recorded. Songs will be mixed to create playback tapes. To avoid pseudoreplication and to avoid testing a specific tape or song, each tape will be used only once. Each male will be played the songs of strangers, to avoid neighbor recognition (and resulting habitation/reduced response). Additionally, to avoid testing differential response to dialect, songs of birds from geographically similar locations will be played to other non-neighbor males. Songs recorded in southern Jackson County will be played to birds in southern Jackson County, northern Jackson County to northern Jackson County and Josephine County to Josephine County.

Playback Procedure

Playback testing will start an hour after sunrise and continue for 4-5 hours. Males will all receive the test treatment, consisting of a 3-min pre-playback baseline period, a 5-min playback period and a 3-min post-playback recording period. Playback in territories less than 150 m apart will not be tested in the same day to avoid double-testing.

Measures of response

I will record the following response variables: singing rate (songs/min) pre-, during and post-playback; time to first song during (from the first song of playback) and post-playback; distance of closest approach to the speaker and time spent within 10 m of the speaker.

Possible Outcomes

There are several possible outcomes for this study. These outcomes can be grouped by singing or physical response. In regards to singing rate, birds will sing more songs per minute after playback; fewer songs per minute after playback or singing rate will be unaffected. Time to first song will either be less, greater or unchanged during and post-playback. Either birds will move close to the speakers and remain, will move close to the speakers but not remain or will not move close to the speakers.

References

American Birding Association. 2011. Birding Code of Ethics. Available from: www.aba.org/about/ethics.html. Accessed February 1, 2012.

Arcese, P., M.K. Sogge, A.B. Marr, M.A. Patten. 2002. Song Sparrow. The Birds of North America, No 704. (A. Poole and F. Gill Ed). Ithaca: The Cornell Laboratory of Ornithology.

Byers, B.E and D.E. Kroodsma. 2009. Female mate choice and songbird song repertoires. Animal Behavior 77:13-22.

Cordell, H.K. and N.G. Herbert. 2002. The Popularity of Birding is Still Growing. Birding 34:54-61.

Cutright, N.J. 1999. Attracting Birds Using Tapes or Compact Discs. The Passenger Pigeon 61(1):3-5.

Dabelsteen, T., P.K. McGregor, J. Holland, J.A. Tobias and S.B. Pederson. 1997. The signal function of overlapping singing in male robins. Animal Behavior 53:249-256.

Erne, N. and V. Amrhein. 2008. Long-term influence of simulated territorial intrusions on dawn and dusk singing in the Winter Wren: spring versus autumn. Journal of Ornithology 149:479-486.

Hyman, J. 2003. Countersinging as a signal of aggression in a territorial songbird. Animal Behavior 65:1179-1185.

Kennedy, E.D and D.W. White. 1997. Bewick’s Wren. The Birds of North America, No 315 (A. Poole and F. Gill, Ed). Ithaca: The Cornell Laboratory of Ornithology.

Kroodsma, D.E. 1973. Coexistence of Bewick’s Wrens and House Wrens in Oregon. The Auk 90: 345-352.

Kroodsma, D.E. 1990. Using appropriate experimental designs for intended hypotheses in “song” playbacks, with examples for testing effects of song repertoire sizes. Animal Behavior 40(6):1138-1150.

Kroodsma, D.E. 2005. The singing life of birds: the art and science of listening to birdsong, pp10-22. Boston: Houghton Mifflin.

Mennill, D.J., L.M. Ratcliffe and P.T. Boag. 2002. Female Eavesdropping on Male Song Contests in Songbirds. Science. 296:873.

Molles, L.E. and S.L. Vehrencamp. 2001. Neighbour recognition by resident males in the banded wren Thryothorus pleurostictus, a tropical songbird with high song type sharing. Animal Behaviour 61:119-127.

Mota, P.G. and V. Depraz. 2004. A Test of Male Song on Female Nesting Behaviour in the Serin (Serinus serinus): a Field Playback Experiment. Ethology 110:841-850.

Osiejuk, T.S, K. Ratyńska and J.P. Cygan. 2007. Corn bunting (Miliaria calandra) males respond differently to alternating and overlapping playback of song. Journal of Ethology 25:159-168.

Otter, K., P.K. McGregor, A.M.R. Terry, F.R.L. Burford, T.M. Peake and T. Dobelsteen. 1999. Do female great tits (Parus major) assess males by eavesdropping? A field study using interactive song playback. Proceedings of the Royal Society B: Biological Science 266:1305-1309.

Reid, J.M., P. Arcese, A.L.E.V. Cassidy, S.M. Heibert, J.N.M. Smith, P.K. Stoddard, A.B. Marr and L.F. Keller. 2004. Song repertoire size predicts initial mating success in male song sparrows, Melospiza melodia. Animal Behavior. 68:1055-1063.

Şekercioğlu, C.H. 2002. Impacts of birdwatching on human and avian communities. Environmental Conservation 29(3):282-289

Stoddard, P.K., M.D. Beecher, C.L. Horning and S.E. Campbell. 1991. Recognition of individual neighbors by song in the song sparrow, a species with song repertoires. Behavioral Ecology and Sociobiology 29:211-215.

Ward, M.P and S. Schlossberg. 2004. Conspecific Attraction and the Conservation of Territorial Songbirds. Conservation Biology 18:519-525.

Wiley, R.H. 2005. Individuality in songs of Acadian flycatchers and recognition of neighbours. Animal Behaviour 70:237-247.

1 comments:

Anonymous said...

lovely!