image_previewPINE GROSBEAK ( map ): A good flight is expected into southern Ontario because the mountain‐ash berry crop is variable in the boreal forest. Many berries are hard with low moisture content because of the drought. The European mountain-ash and ornamental crabapple crops are poor to fair in southern Ontario so these crops won’t last long. Grosbeaks will be attracted to the usually abundant buckthorn berries and to bird feeders offering black oil sunflower seeds. The Ontario breeding population of this grosbeak is stable.

PURPLE FINCH ( map ): Most Purple Finches will migrate south of Ontario this fall because both coniferous and deciduous hardwood seed crops are very low this year in the Northeast. Purple Finch numbers dropped significantly in recent decades as spruce budworm outbreaks subsided and currently a moderate population decline continues in the province.

RED CROSSBILL ( map ): Red Crossbills comprise at least 10 “types” in North America. Each type probably represents a separate or newly evolving species. Most types are normally impossible to identify in the field without recordings of their flight calls. Matt Young of The Cornell Lab of Ornithology reports that there is currently a large early irruption of Type 3 Red Crossbills (smallest billed type) from the west into eastern North America. Recordings can be made with a cell phone and sent to Matt to be identified (may6 AT Every recording adds an important piece to the puzzle, especially when accompanied by notes on behaviour and ecology, including tree species used for foraging and nesting. Matt emphasizes that the conservation of call types depends on understanding their complex distributions and ecological requirements.

WHITE-WINGED CROSSBILL  ( map ): With very poor spruce cone crops in the Northeast, most White-winged Crossbills will likely stay this winter in the Hudson Bay Lowlands, northwestern Ontario and western Canada where spruce cone crops are generally very good. They will be virtually absent from traditional hotspots such as Algonquin Park where spruce crops are very low. Wandering birds may show up throughout the Northeast.

COMMON REDPOLL  ( map ): There should be a good southward flight because the white birch seed crop is poor to fair across the north. Watch for redpolls on birches and in weedy fields and at bird feeders offering nyger (preferred) and black oil sunflower seeds. Check flocks for the rare “Greater” Common Redpoll (subspecies rostrata) from the High Arctic. It is reliably identified by its larger size, darker and browner colour, longer/thicker bill and longer tail in direct comparison to “Southern” Common Redpolls (nominate flammea subspecies). Note: The notion of a “biennial periodicity” that redpolls irrupt south every second winter is not supported by records in Atlantic Canada (Erskine and McManus 2003). The authors concluded that “irregular abundance but near-annual occurrence” of redpolls in the Atlantic Provinces is a better explanation than a two year cycle. Similarly redpolls were recorded on 32 of 38 Christmas Bird Counts in Algonquin Park (Lat. 45.5 N), Ontario.

HOARY REDPOLL  ( map ): Check redpoll flocks for Hoary Redpolls. There are two subspecies. Most Hoaries seen in southern Canada and northern United States are “Southern” Hoary Redpolls (subspecies exilipes). “Hornemann’s” Hoary Redpoll (nominate subspecies hornemanni) from the High Arctic was previously regarded as a great rarity in southern Canada and the northern United States. In recent decades a number have been confirmed by photographs. Hornemann’s is most reliably identified by its larger size in direct comparison to flammea Common Redpoll or exilipes Hoary Redpoll. Caution: White birds loom larger than life among darker birds and size illusions are frequent.

PINE SISKIN  ( map ): Some siskins currently in the Northeast should move south this fall and winter because cone crops are poor. However, siskins are an opportunistic nomad wandering east and west continent-wide in search of cone crops. Most siskins will probably winter in northwestern Ontario and western Canada where cone crops are generally very good. Major southward irruptions occur when cone crops fail across most of North America.

Western hummingbirds in the East–set your feeders out!!

featureImage_summaryEast of the Mississippi, it is well-known that there is only one expected hummingbird–the familiar Ruby-throated Hummingbird. Ruby-throateds typically arrive in April and the bulk have departed by the first of October. However, any hummingbird seen after about 15 October is more likely to be a rare western species than a Ruby-throated! The excitement of one of these western visitors prompts many people to keep their hummingbird feeders hanging until late fall, or even all the way through spring. The yield is high; some homeowners as far north as New Jersey and Massachusetts have had multiple appearances by rare hummingbirds. Try your luck and set out a feeder; below we discuss the possible species, give some tips on attracting late hummers, and discuss the identification of difficult species.

NOTE:  The discussion below will focus on the East coast, but the trends discussed here are equally applicable to Canada, the Midwest, the Gulf Coast (rich in wintering hummingbirds), the West, and even south-coastal Alaska! It seems that anywhere that birders are willing to maintain feeders, late season hummingbirds may arrive.

Fall 2012 has been highlighted by very good numbers of Rufous Hummingbirds (see map here and zoom in for red points to see recent records), a Calliope near Philadelphia in Pennsylvania, and an Allen’s Hummingbird in western Massachusetts since late October. Perhaps some other species will follow soon!

The appearance of these western hummingbirds is a phenomenon that has been realized only recently. Starting in the mid-1980s, each ensuing year has seemed to reveal more hummingbirds of more species in the late fall. In Maryland for example, one Rufous Hummingbird was recorded per decade from 1952 to 1981; in the 1980s there were two; from 1990-1993 there were four; from 1994-1997 there were seven; and from 1998-2000 there were eight. The trend has continued along this trajectory, with more Rufous Hummingbirds appearing in each subsequent year. The state’s first Calliope came in 2004, followed by one in 2006 and another in 2007; an Anna’s Hummingbird occurred in 2005. What will 2012 hold?

From October to January, Rufous Hummingbird is the most common species by far in the East, outnumbering other species by up to ten to one. This species, which may sometimes arrive on their breeding grounds in Alaska before the ice breaks, are particularly well adapted to cold weather. Females and immatures occur in the East with regularity from mid-October on, with arrivals peaking from mid-October to late November. Several individuals have wintered successfully as far north as Massachusetts, where one female (affectionately named “Rufy”) returned to successfully winter in a Bay State greenhouse for at least six years in a row (1996-2002). It appears that immatures that stray to the East and survive the winter are likely to return in the following year, and there are numerous records of banded birds reappearing in subsequent years. Several remarkable banded birds that have been captured in the Southeast and recovered near or on the breeding grounds (e.g., one Virginia Rufous was recovered in Montana, and was found back in Virginia the next winter!). Survivorship of such birds probably also account for increasing ratios of adults noted in the East. Some adult males may appear as early as July or early August, corresponding to their migration patterns in the West. Adult females arrive later (September or October, typically), while the immatures are the latest to appear. Rufous is certainly not the only species possible though–the pool of additional species is large. In addition to Ruby-throated and Rufous, three others have been recorded with regularity in recent years and eight others (13 species in all) have appeared at least once on the East coast: Calliope, Black-chinned, and Allen’s are all occurring annually (or nearly so) from North Carolina north; Broad-billed, Anna’s, and Broad-tailed all have multiple records, and Buff-bellied, Magnificent, and Green Violetear all have a handful. The rarest of the rare, Blue-throated Hummingbird, Violet-crowned Hummingbird and Green-breasted Mango have each occurred once, once, and twice, respectively. See Appendix A for help with identification and Appendix B for more detail on these species and their occurrence on the East coast.

It is worth pointing out, though, that late-season Ruby-throated Hummingbirds are on the upswing as well. In the Carolinas, where wintering Ruby-throateds were once unheard of, the species now occurs regularly on several coastal Christmas Bird Counts where it is even more likely than Rufous Hummingbird. To the north, there are a growing handful of records of Ruby-throateds appearing at feeders in November, December, and even attempting to winter. So don’t rule out the expected summer hummingbird, but do remember that it may not be the most likely option after November.

Birders hosting rare western hummingbirds should consider having their hummingbird banded for species identification and to contribute to our body of knowledge on their movements. A fair number of hummingbirds ARE recovered. Note that one in Vienna, VA, in 2007 disappeared late in the season and moved 15 mi southwest. We know this only because of the banding efforts. Others in Louisiana and the Gulf Coast are known to return to the same feeder year after year and the amount of fascinating information the banders down there generate is incredible. The danger to the bird is minute and the information to be gained is vast. Contact us ( or send a post to your local listserv to try to contact a bander in your area.


Birders hoping to attract any of these late season hummingbirds should get their feeders up NOW, and not take them down until mid-December or later.

A few tips:

* Put your feeder up near areas of good cover (especially evergreens like cedars, boxwoods, hollies, etc.) if possible. In cold weather hummingbirds will need these areas for roosting and the better the protection, the better for the bird. Weedy areas (such as those with lots of goldenrod) may hold insects which can provide good supplemental energy for the hummingbird as well.

* If cold weather (below freezing) is forecast, you should take your feeder inside at night and put it back out in the early morning. Some people have rigged up small heaters for their feeders to keep them thawed. Some have used a low watt heat lamp rigged up in an outdoor hanging fixture (like the lamps used raising baby chickens) with the feeder hanging under the lamp. Be aware that if the water in the feeder freezes, the hummingbird may not survive long.

* If you have any late season flowers those will help to attract late hummingbirds also, and may be better than a feeder at least as long as the flowers survive. By clipping blooms that appear early, you can manage your garden to peak later in the season. Several websites discuss hummingbird plantings and some also recommend which plants are hardy enough to last in cold weather. Various types of Salvia (Sage) are the perennial favorite late-blooming flower for hummingbirds, and may last into November in the Northeast. Particular favorites are the red-flowering Salvia spendens and Pineapple Sage Salvia elegans. Late fall hummingbirds have also been observed visiting Lobelias, Bee balm Monarda didyma, and jewelweed. Also Salvia leucantha (striking white flowers protruding from velvety purple calyces) known as Velvet Sage or Mexican Bush Sage, and Salvia guaranitica (blue) Anise Sage (Black and Blue is a favored variety) are excellent and may bloom until the first frost or beyond. Native trumpet honeysuckle Lonicera sempervirens is another good late blooming hummingbird plant. Trellised in a protected spot, this may remain blooming and re-bloom in late autumn and winter warm spells. Blue-black Sage Salvia guaranitica is harder to find, but may bloom from May until the first frost. Turtlehead, both the wild white and the cultivated pink, bloom well into September and later even as far north as Maine.

* It has been suggested that hanging lots of red Christmas ribbon, red surveyor’s tape, and other red items around the yards may help to be sure that hummingbirds do not pass you by. Some believe the hummingbirds fly down pathways (like roads) and have trails of red leading from the road up to their house. It also might be a good idea to plant other late blooming flowers (like petunias and mums) even though they do not provide nectar for hummingbirds.

Cave Swallows: already in East, and more coming (and even more after that!)

featureImage_summaryWhen Cave Swallows arrive, it is probably fair to think of them as a conspicuous indicator of a vagrancy event. Other species with the same general source regin (Texas and northern Mexico) are likely to be transported similarly in the same conditions, albeit not in flocks and not in comparable numbers. Ash-throated Flycatcher is perhaps on of the more regular such species, so birders should be on high alert for them in these next few weeks as well. One in Massachusetts last weekend was the first of the fall on the East Coast, but more should follow. A couple “Audubon’s” Yellow-rumped Warblers have appeared in Massachusetts and Nova Scotia and several Western Kingbirds have been around as well. Other birds to think about if there are lots of Cave Swallows next week are things like Townsend’s, Black-throated Gray, and MacGillivray’s Warblers, Western Tanager, Franklin’s Gull, Bell’s Vireo, Say’s Phoebe and more. Long shot possibilities include Sage Thrasher, Tropical or Cassin’s Kingbird (The first for Minnesota was recently found), western Empidonax (Hammond’s, Dusky, Gray, or Pacific-slope/Cordilleran). When Cave Swallow reports start to increase in your area, be aware that there may be some rare birds hiding in the bushes too!
 Fig. 2. Ash-throated Flycatcher at Squaw Rock Park, near Boston, MA, 5 Nov 2012. This is one of the other “indicator species” along with Cave Swallow, that November western vagrancy is under way!

Lingering Effects of Hurricane Sandy

Hurricane Sandy and the associated North Atlantic high pressure and Great Lakes low pressure system really did shake up the birds in the eastern United States, much like one of those little snowglobes. Pelagic birds were inland, overland migrant waterfowl were grounded, Arctic birds were south, western birds made it east, and some European birds even crossed the ocean. We are planning an analysis story about this colossal storm and its effects on birds. In the near term suffice to say some of Sandy’s shakeup may still be visible in the Northeastern avifauna and includes some interesting birds that you could find in your area. Below are two to think about.

Northern Lapwings!

Six confirmed Northern Lapwing reports from Massachusetts (3), Maine, New Jersey, and Newfoundland are surely indicative of a pattern that had been shaping up for the past 2-3 weeks. Strong easterly winds over the North Atlantic are likely responsible not only for driving Sandy ashore in New Jersey (rather than allowing it to travel the same route as Wilma in 2005) but also for transporting lapwings from Europe to North America. Please visit the BirdCast site for a much more detailed account on how this probably happened!
In the meantime, now that lapwings are here, they will probably float around the Northeast for a while and may surprise you at a local agricultural field, golf course, turf farm, or pasture. Anywhere that Killdeer occur in the East should be checked for Northern Lapwing this fall and winter. The species has successfully wintered in several East Coast states, so the lapwings that arrived last week might still be around in March!
Addenda 13 Nov 2012: News of at least six more Northern Lapwings buzzed across birding hotlines (and eBird Alerts) this weekend: In Nova Scotia, one was photographed in Shelburne Co. on 11 Nov and on Long Island, NY, one was photographed at Robert Moses SP on 8 Nov and two popped up at Deep Hollow Ranch, Montauk, 10-11 Nov. In addition, one at the Cumberland Farms fields in Middleboro, MA, appeared 11 Nov and was enjoyed by many while another appeared nearby on 12 Nov! Surely there are more out there, so be sure to check likely spots near you!
Northern Lapwing by Sam Galick
Fig. 3. Northern Lapwing in Allentown, Mercer Co., NJ, on 8 Nov 2012. See the eBird checklist from shocked eBird reviewer Sam Galick here.

Slingshot Passerines

The days after Hurricane Sandy’s landfall saw the appearance of a suite of unseasonably weird Neotropical migrants from New Jersey north to Maine and inland to Ontario. It is likely that this array of migrants, including Eastern Wood-Pewee, Northern Parula, Bay-breasted Warbler, Magnolia Warbler, Indigo Bunting, and several others were migrating between the US and the Greater Antilles en route to Central and South America when they were “sucked in” to the massive circulation around Sandy. Check the Birdcast site for more details.

Winter Finch Superflight!

Matt Young provided a look at what is going on with winter finches and characterizes this year as a “superflight”, with essentially all finch species on the move or soon to be on the move.

From Matt: The last superflight in the East occurred in 1997-98, and what is even more exciting about this year’s movement is that it includes finches in both the West and the East.
So far we’ve already seen large movements of  Pine Siskin, Red Crossbill and Red-breasted Nuthatch (an honorary finch) on both coasts. All three have shown up farther south than typical. Red-breasted Nuthatches have been reported in central Florida and throughout the Gulf Coast states. Pine Siskins have smashed records at several sites including Hawk Ridge, Minnesota and Cape May, New Jersey. A flight on Long Island on 21 October yielded an amazing estimate of 20,000 siskins.  Purple Finches are already being reported well into the Southern Appalachians.
Evening Grosbeaks, that favorite feeder bird from yesteryear, looks to be making its largest eastward push since 1997-98. In recent years Evening Grosbeaks haven’t appeared in Pennsylvania or Connecticut until November and December, with scarcely any even then, but this year made their first appearances at the end of September. Evening Grosbeaks have already reached Maryland, West Virginia and Delaware, and some should be expected into the Carolinas and perhaps the mountains of Georgia this year.
After an unprecedented  Red Crossbill flight that materialized in August across the Northern Tier States, crossbills look to be on the move again. In the last two weeks both Red and White-winged Crossbills have been reported nearly daily at Whitefish Point in the Upper Peninsula of Michigan and at Hawk Ridge in Minnesota. Migrating Red Crossbills have also been reported several times in recent weeks at Hawk Mountain in Pennsylvania, with others in Massachusetts. As was true earlier in the fall, nearly all of the recordings received have been  Type 3 (see more on crossbill types here). People in the Southern Appalachian States should be on the lookout for Type 3 (and any other crossbill type), which has only one record to date for North Carolina. White-winged Crossbill has hit the East in force in the past few days, with early November reports en masse from Maine to Rhode Island and the vanguard reaching as far south as Maryland. Type 2 Red Crossbills appear to be moving from the Rockies onto the Great Plains. They have been documented with audio recordings as far east as Illinois and Missouri during the first week of November.

As we now head into late October, early reports strongly suggest  Bohemian Waxwing (another honorary finch),  Pine Grosbeak and redpolls are on their way too. Bohemians have been reported in several Northeastern states, Pine Grosbeak in Massachusetts and redpolls in Connecticut, and it’s still only early November. Look for redpolls at New York feeders by the end of November. With the heat and drought of the past summer, it looks like this year could be a very interesting winter for finches across much of the country. As discussed in my crossbill piece, there are two things to expect: 1) because there’s a lack of natural food across large sections of the continent, it could be an amazing year at feeders, and 2) the Mid-Atlantic States (and perhaps Carolinas) could experience a superflight not seen in 15 years!

Stealth migrants and the importance of reporting common birds
Detecting movements of “resident” species is much more challenging. One of the best ways of doing this is to make repeated counts from a single area. Understanding the full scope and magnitude of these movements requires observations from throughout a species range. Looking at eBird records, it appears that a stealth movement of Black-capped Chickadees may already be underway. Apparently migratory flocks have been noted in portions of the Great Lakes and New York. Observers should watch carefully for this species south of range.

Climate Change Affects the Flight Period of Butterflies in Massachusetts

130213114701-largeIn a new study, Boston University researchers and collaborators have found that butterflies show signs of being affected by climate change in a way similar to plants and bees, but not birds, in the Northeast United States. The researchers focused on Massachusetts butterfly flight periods, comparing current flight periods with patterns going back more than 100 years using museum collections and the records of dedicated citizen scientists. Their findings indicate that butterflies are flying earlier in warmer years.”Butterflies are very responsive to temperature in a way comparable to flowering time, leafing out time, and bee flight times,” says Richard Primack, professor of biology and study co-author. “However, bird arrival times in the spring are much less responsive to temperature.” As a result, climate change could have negative implications for bird populations in the Northeast, which rely on butterflies and other insects as a food source. The team, which includes Caroline Polgar (Boston University), Sharon Stichter (Massachusetts Butterfly Club), Ernest Williams (Hamilton College), and Colleen Hitchcock (Boston College) will publish its findings in the February 12 online edition of the journal Biological Conservation.

While the effect of climate change on plant and bird life cycles in eastern North America has been well examined, studies of the effects of climate change on insects are rare, so these findings represent an important contribution. This new study investigated whether the responses to climate warming in Massachusetts of ten short-lived butterfly species known as elfins and hairstreaks are similar to responses seen in plants, birds and bees. Another unique feature of this study is its use of data from museum collections as well as data gathered by the Massachusetts Butterfly Club, a group of dedicated citizen scientists who love butterflies. Use of this data gave the researchers an opportunity to compare butterfly flight periods dating back to the late 1800s.

The researchers obtained over 5000 records of butterflies in flight using museum collections (1893-1985) and citizen science data (1986-2009), then analyzed the data using statistical models to determine how butterfly flight times are affected by temperature, rainfall, geographic location, and year.

The researchers found that the start of the butterfly flight period advances on average by two days for each degree Fahrenheit increase in temperature. The response of these butterfly species to temperature is similar to plant flowering times and bee flight times and is significantly greater than bird arrival times, which increases the likelihood of ecological mismatches with migratory birds arriving after the first spring flush of their insect food.

The researchers also found that observations by citizen science groups such as the Massachusetts Butterfly Club were an effective and largely untapped source of information that could be used to investigate the potential impacts of climate change on butterflies. Such data provides an opportunity to inform conservation policies on these species and associated habitat. While data from museums was helpful, it was less abundant and therefore less useful than the citizen science dataset.


Blackbirds in the Spotlight: City Birds That Experience Light at Night Are Ready to Breed Earlier Than Their Rural Cousins

130213114701-largeStreet lamps, traffic lights and lighting from homes are causing a rise in our night-time light levels. For some time now, scientists have suspected that artificial light in our towns and cities at night could affect plants, animals and us, humans, too. Studies, however, that have tested this influence directly are few. Scientists from the Max Planck Institute for Ornithology in Radolfzell, Germany, recently investigated how light conditions in urban areas at night affect European blackbirds (Turdus merula). They found that animals exposed to low night-time light intensities, comparable to those found in cities, develop their reproductive system earlier: their testosterone levels rise and their testes mature earlier in the year. They also begin to sing and to moult earlier. The ever-present light pollution in cities may therefore exert a major influence on the seasonal rhythm of urban animals.

For many species, the seasonal change in day length is one of the most important environmental signals in controlling daytime rhythms (e.g. sleep-wake cycles) and seasonal ones (e.g. breeding season). People have long been exploiting this in areas such as agriculture: egg production in battery farming can be increased by altering the length of day with the help of artificial lighting.

City-dwelling animals are now not only exposed to natural light conditions, at times they also experience extreme levels of lighting as a result of artificial light. But what effect does artificial light have on the time-of-day and seasonal organisation of these urban animals? To answer this question, it is first crucial to know what light intensities the birds are actually experiencing at night. Therefore, a group of scientists working with Jesko Partecke from the Max Planck Institute for Ornithology tagged several urban blackbirds with light loggers to measure the average light intensities the birds were exposed to during the night. “The intensities were very low — 0.2 lux. That’s just one-thirtieth of the light emanating from a typical street lamp,” says the scientist.

Yet even such low values are sufficient to make the gonads of male blackbirds mature earlier. The scientists exposed wild-caught city and forest blackbirds to lighting intensities of 0.3 lux at night over a period of ten months. “The results were astonishing: The birds’ gonads grew on average almost a month earlier than those of animals that slept in the dark,” explains Partecke. The scientists also measured the level of testosterone in the birds’ blood as another indicator of the animals’ readiness for breeding. They found that the level rose earlier if the birds had been exposed to light at night. Song activity also got out of rhythm as a result of the low night-time light intensity; the animals began singing around one hour earlier. “All of this indicates that, from a seasonal perspective, the animals are ready to breed earlier,” explains Partecke. However, animals living with night-time light not only exhibited an advanced onset of breeding, they also moulted towards the end of the breeding season a lot earlier than birds that spent their nights in the dark. “These findings are clear evidence that the artificial light we find in towns and cities can dramatically change the seasonal organisation of wild animals.

The scientists do not yet know what causes the advanced onset of breeding. It could be that the artificial night-time light has the effect of extending the day length for the animals. Or perhaps the light makes the birds continue hunting for food at night and put the additional energy into reproduction. Equally, the light may also influence the animals’ metabolism and the altered metabolism might be what causes earlier gonad growth. Birds are more active in the daytime if they are exposed to light at night.

Nor is it clear whether the city blackbirds’ advanced breeding offers an advantage or whether it is merely an unintended side effect of the lighting. “Blackbirds in the city are able to breed earlier in the year due to the artificial light and can produce more young in a year as a result,” explains Partecke. “But only if the nestlings have access to enough food.” Otherwise, the advanced onset of breeding could turn out to be an evolutionary disadvantage for blackbirds. With this in mind, the next aspect the scientists plan to study in their field research is the impact of night-time light in urban areas on the birds’ fitness.


Real Angry Birds ‘Flip the Bird’ Before a Fight: Biologists Use Robots to Study Attacks of Male Swamp Sparrows

130129100253-largeMale sparrows are capable of fighting to the death. But a new study shows that they often wave their wings wildly first in an attempt to avoid a dangerous brawl.

“For birds, wing waves are like flipping the bird or saying ‘put up your dukes. I’m ready to fight,'” said Duke biologist Rindy Anderson.

Male swamp sparrows use wing waves as an aggressive signal to defend their territories and mates from intruding males, Anderson said. The findings also are a first step toward understanding how the birds use a combination of visual displays and songs to communicate with other males.

Anderson and her colleagues published the results online Jan. 28 in the journal Behavioral Ecology and Sociobiology.

Scientists had assumed the sparrows’ wing-waving behavior was a signal intended for other males, but testing the observations was difficult, Anderson said. So she and her co-author, former Duke engineering undergraduate student David Piech (’12), built a miniature computer and some robotics, which the team then stuffed into the body cavity of a deceased bird. The result was a ‘robosparrow’ that looked just like a male swamp sparrow, which could flip its wings just like a live male.

Anderson took the wing-waving robosparrow to a swamp sparrow breeding ground in Pennsylvania and placed it in the territories of live males. The robotic bird “sang” swamp sparrow songs using a nearby sound system to let the birds know he was intruding, while Anderson and her colleagues crouched in the swampy grasses and watched the live birds’ responses. She also performed the tests with a stuffed sparrow that stayed stationary and one that twisted from side to side. These tests showed that wing waves combined with song are more potent than song on its own, and that wing waves in particular, not just any movement, evoked aggression from live birds.

The live birds responded most aggressively to the invading, wing-waving robotic sparrow, which Anderson said she expected. “What I didn’t expect to see was that the birds would give strikingly similar aggressive wing-wave signals to the three types of invaders,” she said. That means that if a bird wing-waved five times to the stationary stuffed bird, he would also wing-wave five times to the wing-waving robot.

Anderson had hypothesized that the defending birds would match the signals of the intruding robots, but her team’s results suggest that the males are more individualistic and consistent in the level of aggressiveness that they want to signal, she said.

“That response makes sense, in retrospect, since attacks can be devastating,” Anderson said. Because of the risk, the real males may only want to signal a certain level of aggression to see if they could scare off an intruder without the conflict coming to a fight and possible death.

Still, the risk of severe injury or death didn’t keep the studly males from swooping in and clawing at the robotic intruder, whether it wing-waved or not. “It’s high stakes for these little birds. They only live a couple of years, and most only breed once a year, so owning a territory and having a female is high currency,” Anderson said.

She and her team had planned to test how the sparrows use wing waves combined with a characteristic twitter called soft-song to show aggression and fend off competition. But the experiment may be on hold indefinitely because robosparrow’s motor seems to be burned out, and its head was ripped off in an attack, a true fight to the death. sorce