bootstrap analysis

deer browsing and songbirds

The latest issue of the Ibis, the journal of the British Ornithologists' Union, had several excellent papers. One was an overview of the impacts that deer browse has on habitat quality and subsequently bird life. I’d like to highlight some salient points, because they illustrate the interconnectedness of ecosystems, and can serve to help the average person understand that too many deer don’t just mean fewer wildflowers in the woods.

We’ll start with that simple point. Deer browsing changes under- and mid-story vegetation not only by changing the species composition (skewing it towards unpalatable species) but by reducing the abundance and density of trees, shrubs, and vines. For birds, this can mean a loss in available nest sites and roost sites, and an increased vulnerability to nest predation.  This seems fairly intuitive. The impacts of deer browse on the food supply of birds is often less direct.

Deer prefer to eat growing shoots of plants, which not only affects the growth of the plant, but may also delay or prevent flowering. This can reduce the number of pollen-seeking insects on which birds may feed during the breeding season. No flowers means no fruits or seeds, which birds consume later in the season, often fueling migratory flights or providing winter forage. Of course, deer also eat fruit and seeds, putting them in direct competition with birds.

Many insects, such as lepidoptera larvae which are so important to birds feeding nestlings, also prefer to feed on actively growing plant tissue just as the deer do. This paper notes a number of studies have found that these invertebrates can be reduced by deer browse in the vegetation layers that can be reached by deer.

Leaf litter thickness often also changes in forests with high densities of deer. Their browsing can alter the amount of sunlight that reaches the forest floor, and decreased density of trees and shrubs, as well as direct grazing on herbaceous plants, often coincides with more grasses or bare ground. This can all result in reduced number of some types of leaf litter invertebrates that are important to ground foraging bird species.

The New York Times just had a short article on the stupendous increase in White-tailed Deer in the United States -- doubling in population the last twenty years to an estimated 32 million animals. That's 12 million more than were here prior to European settlement, in far less space. The Times graphic shows that here in Michigan, I have a 1 in 86 chance of hitting a deer with my car in the next year, the second-highest odds in the nation.

The Ibis paper (and indeed the entire issue) is available for free at the journal home page.

Gill, R. M. A. and R. J. Fuller. The effects of deer browsing on woodland structure and songbirds in lowland Britain. Ibis 149:119-127.  doi:10.1111/j.1474-919X.2007.00731.x

Here are some links to previous posts I've done that included the impact of deer overpopulation:

• Problematic charisma: White-tailed Deer
• Impact on songbird populations
• Deer eliminating bears
• Impact on invertebrates
• Link to overview article in BioScience

table of contents alert (12)

Assessment of management techniques to reduce woodpecker damage to homes.  E. G. Harding, P. D. Curtis, and S. L. Vehrencamp. 2007. Jrl. of Wildlife Management 71:2061-2073.
People frequently ask me how to prevent woodpeckers from banging on their houses. This study looked at several available control strategies: fake owls, huge eyeballs, loud sound systems, shiny tape, and distracting suet feeders and nest boxes. This was a pretty small-scale study, but it concluded that a reflective metallic tape product called Irri-Tape worked best. The authors also recommended avoiding natural-colored stains and paints on homes if near wooded areas.

Female-limited polymorphism in the copulatory organ of a traumatically inseminating insect. K. Reinhardt, E. Harney, R. Naylor, S. Gorb, M. T. Siva-Jothy. 2007. American Naturalist 107:931-935.
My first thought: "What in the hell is a "traumatically-inseminating insect"? As it turns out, females of the Cimicidae (bedbugs and relatives) have typical genitalia that is used for egg-laying, but not for mating. The males inseminate them by piercing the abdominal wall. The females have thus evolved "paragenitalia," consisting of modifications of the external abdominal cuticle which guide the male's piercing organ toward special internal structures that both receive sperm and contain immune cells which help reduce the septic risks of this type of insemination.

This paper looked at Afrocimex constrictus, the African bat bug, unusual even by Cimicidae standards. Males possess female-like paragenitialia. This apparently evolved because these insects only determine the gender of their partner at the time of mating. The male paragenitalia reduce the costs of being wounded by a piercing from another male, but subtle differences in the external structure -- they are "open" whereas in the female they are "covered" -- may tip off the misguided male partner before piercing takes place. The authors also discovered that females of their study population had two morphs. The external paragenitalia sinuses were either covered (typical) or open, like a male. The female morph with the male--like open sinuses were not pierced as much due to this sexual mimicry, and therefore suffered less damage.

One-sided ejaculation of echidna sperm bundles. (WITH ON-LINE ENHANCEMENTS). S. D. Johnston, B. Smith, M. Pyne, D. Stenzel, and W. V. Holt.  2007. American Naturalist 107:E162-E164.
Some papers just beg to be read. When I received this table of contents alert in my email, I found it quite compelling. An echidna is a "spiny anteater," related to the platypus, which made the subject intriguing enough, but the shouting announcement of on-line enhancements just made it irresistible. The first sentence of the abstract reads:

We report for the first time an unusual ejaculatory mechanism in the short-beaked echidna in which each side of the bilaterally symmetrical, rosettelike glans penis is used alternately, with the other being shut down."

Rather than summarize this paper, I'll just let you have at it: it is open-access. You can even view two videos (the enhancements), one entitled, "Erection Behavior and Ejaculation." I'm only including this paper so that I get a lot of traffic from naughty Google searches.

~~

As an aside, I've noticed a slowly growing trend lately away from dull, dry, straightforward paper titles in peer-reviewed journals to some which are more clever or even whimsical. Here are a few examples:

• When to care for, abandon, or eat your offspring: the evolution of parental care and filial cannibalism (Klug and Bonsall 2007, American Naturalist 107:886-901).
• How to be fed but not eaten: nestling responses to parental food calls and the sound of a predator's footsteps (Magrath, Pitcher, and Dalziell 2007, Animal Behaviour 74:1117-1129).
• Fear, food, sex and parental care: a syndrome of boldness in the fishing spider, Dolomedes triton (Johnson and Sih 2007, Animal Behaviour 74:1131-1138).

ivory-billed woodpecker draft recovery plan comments

Yeah, what David Sibley says.

Times a million. Read it, twice, carefully. Hope somebody pays attention.

(The Ivory-billed Woodpecker Draft Recovery Plan isn't the only one that's all screwed up, ignores science, and bows to politics. Check out the peer review of the Northern Spotted Owl Draft Recovery Plan, and try to breathe slowly.)

table of contents alert (11): dog walking and birds

Four-legged friend or foe? Dog walking displaces native birds from natural areas. P. B. Banks and J. V. Bryant. 2007. Biology Letters. Early online, DOI:10.1098/rsbl.2007.0374.
This paper has received a lot of press as it is on a perennially hot-button topic. Australian researchers did a careful examination of the impacts of dog walking at 90 sites near Sydney. They looked at a variety of bird species within 50 meters of a trail, and observed their reactions to walkers with dogs, walkers without dogs, and neither. The results were clear:

"...Dog walking in woodland leads to a 35% reduction in bird diversity and 41% reduction in abundance, both in areas where dog walking is common and where dogs are prohibited."

It should be noted that all dogs were leashed, and it is my experience that dog walkers frequently let their dogs off leash in wooded areas (I am not alone). That this effect was evident in areas where dogs were commonly walked as well as places where dogs were not allowed indicates that birds do not get used to dogs nearby. Ground-dwelling bird species were impacted at a higher percentage, but people without dogs caused only about half the disturbance.

Before I hear from irate dog owners, let me address some of the JPS (just plain stupid) arguments that tend to crop up. You can see many of them in one form or another in the comments of this random article on the paper.

• Development/habitat loss/humans in general are the biggest problem facing birds, not dogs. This is true. Heart disease is one of the leading causes of death in the United States. That doesn't mean we ignore every other large and small disease, disorder, or injury that causes mortality.  If we added up the impacts of every other threat to bird survival, I'm sure it would come close to or equal the impact of habitat loss. If we all do our part in reducing or eliminating the lesser impacts, the world would be a better place.


• Cats are worse. Outdoor cats are awful, I agree. Keep them inside. Then walk your dog around the block or take it to a dog park. And see above.


• These people are hypocritical. Have they never killed a bird with a car? Had a bird hit their window? See point number one, again.


• Nature always finds a balance. The birds just go somewhere else. The "balance" is increasingly ending up in favor of a few highly adaptable species and simplified, altered ecosystems. In a rapidly urbanizing world, these birds end up not having another place to go, or must attempt to survive in marginal, inappropriate habitat, or in increased competition with other birds seeking the same safe haven.


• The birds just fly away then come back. There is no lasting impact. Many studies have looked at how disturbance (predator, human, etc.) has long-reaching effects on birds, such as time away from foraging, increased energy output, nests left untended, chemical reactions in the body that reduce fitness, etc.


• I suppose foxes and wolves will be next! Because of their territorial nature (and the fact many do not survive well in urban areas), other canids do not occur in the density and abundance of domestic dogs. My study site is part of a 300-acre urban natural area. There are red and gray foxes and coyotes. There are more dogs walked through our area -- where they are prohibited -- in any given week than the population of all three native candids combined. And that's not counting the feral dogs, which have been released or dumped there.


• Dogs have a right/I have a right to walk wherever I want. Nobody is trying to tell you can't walk your dog. Just don't walk it through natural areas. If you can't find someplace near where you live to walk your dog, or your dog needs to run free, maybe you need to live someplace else or not have a dog. I don't have a horse. By the way, if dogs have rights, so do birds.


• Maybe it was the researchers that scared off the birds. What are the effects of researchers on bird populations?  Obviously, having a human observer in place creates an effect. However, that effect was equal for all observations, and the dog impact was still seen and profound. And there are negative impacts associated with some types of wildlife research, but all researchers have an ethical and legal obligation to minimize these impacts or not perform the studies. At least we end up learning something from research; we don't learn anything from disturbing birds walking our dogs.

Usually, I summarize two or three papers in my TOC Alerts. I've rambled on enough, though.

monarch tagging

We are about to use the last of this year's 50 Monarch tags, used to track these migratory butterflies.  I'm sure we'd be done by now, but I spent 10 days completely out of it with a really bad virus; as soon as I got better, Kingfisher came down with it. All better now, and trying to catch up...

Normally we raise a couple dozen Monarchs from eggs and tag those that are the late summer, migratory generation, and use the rest of the tags on butterflies we catch in the yard. This year, we spread out a bit. At a location where I'm doing some insect surveys for a grant project, there is a big field of Tall Boneset (Eupatorium altissimum) along a major river, a great stopover for Monarchs. We tagged a bunch there.

The tags are super sticky, and Monarch wings are much sturdier than other butterflies, so these tags last through the fall migration. At the Mexican wintering grounds of the Monarchs, folks are paid to find butterflies with tags, and a database is maintained with recovery information.

There's more on the  Monarch Watch web site, or this cool article from the New York Times.

 

table of contents alert (10)

Mute Swans' impact on submerged aquatic vegetation in Chesapeake Bay. K. S. Tatu, J. T. Anderson, L. J. Hindman, and G. Seidel. 2007. Journal of Wildlife Management 71:1431-1440.
Chesapeake Bay has been at the center of the Mute Swan control controversy. Defenders of Mute Swans contend that ecological impacts on submerged aquatic vegetation (SAV) in the Bay (and resultant degraded habitat for fish, crustaceans, and other waterfowl) is not due to the swans, but other factors, and that there is little research to back up claims of ecological damage by swans. Well, here we are.

This study measured vegetation characteristics of SAV beds in controls (unfenced), 2-year exclosures, and 1-year exclosures at 18 sites  to quantify the impact of herbivory by Mute Swans. Exclosures were constructed so that other potential consumers of SAV were allowed access (as well as pollution). Mute Swan herbivory had a substantial adverse impact on percent cover, shoot density, and canopy height of SAV. At the end of the study mean percent cover, shoot density, and canopy height in the controls were lower by 79%, 76%, and 40%, respectively, as compared to those in 2-year exclosures.

All shallow water sites (0.50-0.75 m) were predominantly occupied by Mute Swan flocks, and percent cover reduction of SAV was as high as 75-100% at these sites. Mute Swan flocks also predominantly occupied 3 of the 5 deep-water sites (>1 m) and 1 of 7 moderate-depth sites, where there was considerable (77-93%) SAV reduction. The authors recommended that initial emphasis primarily be placed on controlling mute swans in flocks and secondarily on pairs.

White-crowned Sparrow with three legs. A. M. Schiller, K. W. Larson, and J. D. Alexander. 2007. Western Birds 38:1222-223.
A White-crowned Sparrow mist-netted in Oregon in mid-October had a non-functional third leg originating from its cloaca, the first known instance of a bird with a third leg originating from an otherwise normal cloaca.

I don't have anything to add to that.

Off-highway vehicle trail impacts on breeding songbirds in northeastern California. D. C. Barton and A. L. Holmes. 2007. Journal of Wildlife Management 71:1617-1620.
For those who would like quantification of the impact of OHV/ORVs on bird nesting, this study found greater nest desertion and abandonment and reduced predation on shrub nests <100 m from OHV trails than at nests >100 m from OHV trails. Two of 18 species studied were less abundant at sites on trails than at sites 250 m from trails, and no species were more abundant on trails.

help birds far away

Many birders and ecologists are aware of a program called MAPS -- Monitoring Avian Survivorship and Productivity. Initiated in 1989 and administered by the Institute of Bird Populations (IBP), over 500 hundred banding stations across North America use standardized procedures to gather data on breeding birds. The information is used to create indices of reproductive productivity, examine how habitat and weather variables effect nesting success, and determine survivorship of adults and young.

Fewer people are aware that in 2002, IBP started up a sister program, MoSI (the acronym comes from the Spanish "Monitoreo de Sobrevivencia Invernal" or Monitoring Overwintering Survival). These stations (around 150 right now) are located across the American tropics, and the goal is to learn more about physical condition, habitat use and survivorship over the winter, and how various factors impact subsequent breeding activity. Remember that most of "our" breeding birds spend more time on the ground in the tropics in winter than they do here in the breeding season. Yet very little is know about winter ecology, or its link to overall population health.

As you might imagine, there isn't a lot of money floating around Latin America to run banding stations. IBP actively seeks memberships and donations, and for only $300, you can sponsor an individual MoSI station. Awhile back, both my husband and I sent in our sponsorship funds. We have now received information on the stations, including the location and description, a list of the birds banded (and how many) for each year, and photos from the station if available and other stations, too.

"My" station is located in southern Mexico, in Cuernavaca, Morelos state. It is located in pine-oak forest, and has operated since the 2003-2004 season. The top five species there so far are:

1. Blue-gray Gnatcatcher
2. Nashville Warbler
3. Warbling Vireo
4. Dusky Flycatcher
5. Virginia's Warbler

The Kingfisher's station is also in Mexico, further northeast, in secondary and primary forest near Xalapa in Veracruz state. That station began in 2204-2005, and the top five species there are:

1. Gray Catbird
2. Yellow-breasted Chat and Buff-bellied Hummingbird
3. White-collared Seedeater
4. White-eyed Vireo and Orange-crowned Warbler
5. Common Ground-Dove

This is a terrific and extremely worthy program, very deserving of support. If you are considering some year-end donations, or looking for a great charitable gift for a bird-loving friend, sponsor a MoSI station! Read more in an article in Living Bird magazine.

help birds near you!

Rob, of course, wrote about this, but it deserves a little link love. National Audubon has launched a new addition to their Audubon at Home web section called Birds to Help. You can click on three types of landscapes: urban, suburban, and rural, and see a short list of common bird species found in those landscapes (examples of urban birds below, links not live). Each species has a one-page PDF of suggested ways you can provide for their needs.

I love this. People often want to do something constructive to assist birds, but are either overwhelmed by information or don't know where to look to begin with. Birds to Help offers pointed, accurate, manageable tips in a succinct, straightforward format. I often recommend the Audubon at Home web site as a source for similarly-styled advice on bird feeding, healthy yards, etc. Birds to Help is another great tool. Check it out.

cornell strong-arm tactics?

I've been working on another post, but a related item has cropped up that I just can't quite get out of my head, and I'm surprised that there has been relatively little buzz about it.

In the most recent (17 Aug) issue of Science (317:888-892), there is a staff-written piece, Gambling on a Ghost Bird. Birder's World editor Chuck Hagner revealed an acutely distressing fact from this article:

It reveals that members of the Cornell team worked mighty hard behind the scenes to silence skeptics Jerry Jackson, Mark Robbins, and Rick Prum. ... Cornell Lab director John Fitzpatrick [confronted] Jackson in August 2006 ... going so far as to offer him "co-authorship on a future paper” if he would withdraw a letter to The Auk. Jackson’s reply: “That’s not how I operate.” 

Here is the excerpt from the Science piece:

...Fitzpatrick confronted Jackson during an August 2006 meeting in South Carolina and asked him not to publish[*]. Jackson recalls Fitzpatrick heatedly telling him, "You are going to be independently responsible for the extinction of the ivory-billed woodpecker because you are preventing me for raising money for conservation." Shortly thereafter, Fitzpatrick contacted Jackson again and offered co-authorship on a future paper if Jackson would pull his letter. “That’s not how I operate,” Jackson told him.

Earlier, as rumors of Jackson, Robbins, and Prum's paper surfaced, James Tate, then science advisor to former Department of Interior Secretary Gale Norton, called Jackson and told him to "back off." That the Bush administration would try to suppress dissent doesn't surprise me, but Tate is a former assistant director of Cornell Lab of Ornithology, brought into the fold early in the game by Fitzpatrick.

Ever since reading those words, I've been really disturbed.

Like many thousands of other people, I greatly admire what Cornell Lab of Ornithology has done for birds and citizen science. But if the above accusation is true -- and I have heard from friends of Jackson that it is essentially accurate -- it seems unethical at best, and certainly flies in the face of the spirit of fairness, balance, and objectivity of science. I've never been comfortable with Cornell's, let's say, overly optimistic interpretation of the results of their Arkansas search. This latest revelation just puts a fine point on it.

I'm already inclined to withdraw my financial support from Cornell. I have no interest in funding anything more to do with IBWOs, not only because I don't believe they are still extant, but because I feel that Cornell violated my trust. Trying to suppress opposing viewpoints is a form of scientific fraud.

Yet I'd like to see their other work continue. What's the solution here? That Cornell admits they oversold the whole affair? That Fitzpatrick resigns? I don't know. 

What do you think? Is this as troubling to you as it is to me? Let me know in the comments and/or take the poll below. I've just tossed out some options, and you can give multiple answers.

How do you feel about Cornell's behavior regarding the IBWO?
	I believe everything they've said.
	I'm becoming skeptical that their evidence really supported their conclusions.
	If they tried to suppress opposing viewpoints, somebody should resign.
	I have or am considering withdrawing financial support.
	Even if they weren't completely above-board, it doesn't matter to me.
pollcode.com free polls

[* - This is the letter Fitzpatrick did not want Jackson to submit] Jackson, Jerome A. (2006): The public perception of science and reported confirmation of the Ivory-billed Woodpecker in Arkansas. Auk 123:1185–1189.

table of contents alert (9)

Weather-related mass-mortality events in migrants I. Newton.  2007.  Ibis 149: 463-467.
In spring 2007, there was a prolonged, widespread freeze over the eastern U.S., the likes of which had not been seen in many decades in some places. Reports of mass deaths of swallows were reported on the Internet, and I predicted this event would have a profound impact on numbers of many species of migrants which were moving towards their breeding grounds. This notion was a bit poo-poohed when I aired it. This paper compiled weather related mortality events from European and North American bird journals, and noted from what little data was available that unseasonable cold after arrival in breeding areas reduced local breeding densities from 25-90%, depending on species and area, and populations required several years to recover. None of the events mentioned were as prolonged or covered such a wide geographic area as the 2007 freeze. Aside from swallows, determining the impact of this freeze for other insectivorous migrants may take some time; it won't be easy to tease out from breeding bird data since these birds were mostly still en route to their nesting areas.

Long-distance dispersal of plants by vehicles as a driver of plant invasions. M. Von Der Lippe and I. Kowarik.  2007. Conservation Biology 21:986-996.
Roadways often act as corridors of dispersion for plants. This study sampled seeds from the insides of several long tunnels in the Berlin area to exclude any seeds not deposited by traffic. Thousands of seeds of over 200 species were found in the tunnels. Half of the species and over half of individual seeds were non-native species, and 19.1% of species were highly invasive. The species composition of the tunnel seeds was more similar to the regional roadside flora of Berlin than to the local flora around the tunnel entrances. The authors concluded that long-distance dispersal by vehicles was a routine rather than an occasional mechanism for invasive plants.

Effects of earthworm invasion on plant species richness in northern hardwood forests. A. R. Holdsworth, L. E. Frelich, and P. R. Reich. 2007. Conservation Biology 21:997-1008.
I have written before about the effects on non-native earthworms on forest ecology -- and that no earthworms are native to most northern forests in North America. This study sampled earthworms, soils, and vegetation, and examined deer browse, in 20 forest stands in two national forests in Minnesota and Wisconsin. The mass of Lumbricus earthworm juveniles was significantly and negatively related to plant-species richness in both forests. Typical indicator species of highly invaded sites were ash (Fraxinus) seedlings, the sedge Carex pensylvanica, and jack-in-the-pulpit. Wild sarsaparilla and rose twisted stalk were significant indicators of lightly invaded plots in both national forests.