Posts Tagged ‘Research’

Information is important. With information each of us as individuals, and our society as a whole, can learn about the world. With information, we can all make decisions that make sense. With information, we can all discuss ideas.

Without information none of that is possible. Without information, we are, at best, at the mercy of our current, limited knowledge, and our base instincts. Without information we are, at worst, at the mercy of the limited knowledge and instincts of someone else.

This is why the gag order, and insistence that all reports and data be pre-screened before release to the public, issued by the President to the EPA are so concerning to me, and I think should be so concerning everyone else. This is exactly the kind of action that limits access to, and spread of, information. It will only hamper all of our abilities to operate as rational, critically thinking individuals. It is the kind of action that is put in place to control what we, as citizens, know and when we know it. This is censorship and it has no place in science or a free society.



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Being able to see what is in front of you is an important skill. This may seem like one of those statements that is so obvious that there is no point making it. However, it seems to be a skill that is difficult to master. Recently, I have been running into this issue a lot. As I have mentioned in other posts, I am a Teaching Assistant for an introductory biology class at U.C. Davis on Phylogenetics and Biodiversity. A large part of this class is exploring how organisms (plants, animals, fungi, microbes, etc.) are similar to, or different from, one another. This requires students to actually look at organisms and determine these similarities and differences, and here lies the rub. Getting college students to simply describe what they see is frequently a real challenge. We will be looking at an organism and when I ask them to tell me what they see, they immediately begin telling me what kind of organism it is. That is not the same thing. I am asking them to describe what is in front of them (a soft body, two openings for water, no skeletal support system) and instead they are giving me labels (a Tunicate).

And this phenomenon is not limited to college students. I have been a birder all my life and sometimes lead birding walks for various organizations. I have often asked other birders I am with to tell me what they see when looking at a particular bird. Their tendency, young birder and old, is to start attempting to put a name on the bird. Instead of looking at the bird and letting what they actually see guide them to an identification, they jump ahead and start putting names on the bird that often basically amount to guesses. Over and over again, in so many different settings, I have seen this kind of thing happen, and it is always because the people looking at the world are not able to slow down and really see it!

This need to rush to a label is really troubling for me. I know humans have a sort of innate tendency to want to put things in boxes, but surely we should be able to overcome that tendency. We should be able to look at an object and just take it in. Make note of what you see before you and let that information guide your thinking. The desire to put a label on something reverses this process. By putting a label on an object, we are biasing what we think that object will be like.

I have seen this happen in the birding world so many times! Someone will see a bird. Great! They will not know what it is right off the bat. Nothing wrong with that! So they will ask for help in identifying it. Wonderful! Then the problems start. Instead of looking at the bird are really seeing what is there to see they jump to the identification, the label. Since they did not know what the bird was, the label they jump to is often just a guess and is usually wrong. And here is where it gets weird. Once they made that jump to the incorrect identification the birders will start saying that they see field marks that are not there, but that are consistent with their jumped to label. Let me say that again. They start seeing things that are not there! How we think about the world alters how we perceive the world. By giving in too quickly to the urge to put labels a thing, we can influence how view the thing. This gets downright dangerous in the world of science.

I would like to encourage everyone (scientists and non-scientists alike) to do, would be to look at an object and really see what it has to show you. The identification of an object is the end goal, not where we should be starting. Instead, the first step must be to make careful observations. Just look at the thing and see what is actually there without making any jumps or judgment calls. Then the information from those observations needs to be carefully thought about. Then, after you have absorbed and considered what is in front of you, let that information guide you to an identification, if possible.

But really see the world! Don’t see what you want to see, or what you think you are going to see, or what you think someone else is expecting you to see. Just let yourself take a moment to look carefully, and really see.

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Some of my fellow Animal Behavior graduate students and I have started a new blog called The Ethogram! An ethogram is a list of established behaviors of an animal that is being studied. This is in reference to the strong animal behavior bent to the blogs material. The aim of this blog is to make animal behavior research more available and to bring it to the attention of a wider audience. Take a look at:


and follow us if you think the information will be of interest!

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At this time of year, all across the northern hemisphere, people are starting to go out to particular places that combine specific geographic characteristics.  They are places that generally have reliable winds out of the north, they are elevated up above the surrounding landscape and so give a good vantage of the area, and they are situated where the land is constrained in some way (by coastlines or mountain ranges), and they are at mid-latitudes such that there is a large amount of potential breeding areas to the north and is not south of the wintering areas.  The places that meet these requirements and have these characteristics are places where migratory birds of prey tend to concentrate.  If you look at a map of the world, you can predict where the good hawkwatch sites are.  Anywhere that is shaped like a funnel with the wide end to the north and the narrow tip to the south will likely be the site of a fall hawk migration.  There is a hawkwatch on the Rock of Gibraltar at the tip of the Iberian peninsula funneling birds out of western Europe and constrained by the Mediterranean Sea and the Atlantic Ocean.  There is a hawkwatch in Ilat, Israel funneling birds out of eastern Europe and western Asia and constrained by the Mediterranean and the Black and Caspian Seas.  There is a hawkwatch on the Thailand/Malaysian peninsula funneling birds out of eastern Asia and constrained by the Gulf of Thailand and the South China Sea to the east and the Bay of Bengal and the Andaman Sea to the wet.  There are a series of hawkwatches along the funnel of central America funneling birds out of North America and constrained by the Pacific Ocean and the Gulf of Mexico.  The largest of these hawkwatches is also the largest hawkwatch in the world at Vera Cruz, Mexico.  The birds are drawn by the tailwinds that help to push them south and guided by the coastlines and ridges in the attempt to avoid large bodies of water or open land that lack the aerodynamic aid of thermals and updrafts.

And the people are going out to high points in such areas to count the raptors as they pass by.  Hawkwatchers all around the world are starting their yearly endeavors to monitor the populations of migrating birds of prey.  Some of these counts are done only one or two days a week while others have people out every day of the season.  A large majority of them use volunteers, to at least some extent, and this is an excellent way for anyone to become a citizen scientist and add to the understanding of birds of prey.

By conducting these counts every year, the size of raptor populations can be tracked.  If drops are seen, the causes of these drops can be investigated.  One of the most famous example of this process was when Rachel Carson noted a drop in the numbers of the young Bald Eagles and Peregrine Falcons during migration.  The investigation of the extremely high rates of nest failures in these species, led to the finding that the nests were failing because the eggs being laid in them had very thin shells and so cracked when an adult bird attempted to incubate them.   When egg shell fragments were tested, they were found to contain very high levels of the pesticide DDT and its derivative DDE.  All this led to two major events.  One was that Carson wrote the book “Silent Spring” which grabbed the attention of the nation and was one of the large steps in getting DDT banned.  The second was that researchers began taking eggs out of nests and incubating them in captivity.  With the help and knowledge of falconers, they were able to raise the chicks that hatched from these eggs and release them into the wild where they have succeeded in thriving and breeding and so bringing the populations of a number of species back from the edge of extinction to large and stable populations.  And none of this would have happened if people had not been going out into hill tops and mountain ridge-lines to count the birds as they pass by each year.

So go out and join a hawkwatch near you, or start your own!  There are many organizations that either run hawkwatches or can help you start one.  The data from all these sites is compiled so that trends across large area, or even continents, can be monitored.  But it only works if there are people out counting.

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I have been studying the Evening Grosbeak for the past three years for first my Master’s degree and now my Ph.D.  Studying this species has had many wonderful benefits.  Since they are commonly found in mountainous areas, I have traveled to, and camped in, many parts of the Sierra Nevada, Cascade, and Rocky Mountains.  I have met wonderfully generous people interested in the birds that share this world with us.  I have had the opportunity to glimpse some of the details of some aspects of the lives that members of this species lead.  However, one facet of working with this species that has not been quite so wonderful is the bite that these birds can deliver!  It is amazingly powerful!  I have been banding birds of many species for over a decade now, and in that time I have been bitten by quite a few birds.  I have been bitten by Cardinals, I have been bitten by American Kestrels, and I have bitten by Downy Woodpeckers just to name a few of the more painful species.  I have even been bitten by Black-headed and Blue Grosbeaks, which have a similarly shaped beak, though they are not actually closely related to the Evening Grosbeak.  None of those bites prepared me for the first time I was bitten by an Evening Grosbeak.  I was in Oregon on my first trip out to do field work on my project and had caught my first Evening Grosbeak in my mist net.  I was very excited and began spreading the net open so that I could untangle the bird.  Just as I was reaching my hand in to get a hold of the bird, it suddenly turned its head and clamped its beak down on my finger.  Wow, did it hurt!  If you take a pair of pliers, put the side of one of your fingers between the jaws, and squeeze tight, you will have some idea of what my finger was feeling at this point.  And not only do they have the strength to cause some serious pain, but they have the stamina to continue applying that crushing pressure seemingly indefinitely!  I reached my other hand in and tried to pull the bird away from my hand, but it would not let go.  I waved my other hand around near its head, which sometimes works to distract a bird, but it would not let go.  My eyes now watering from the pain, I even tried to pry the birds’ beak off of me with my other hand, but it would not let go!  Finally, it seemed to grow bored with my finger and let go and started screaming at me instead.  Over the next two days, I caught about 30 Evening Grosbeaks and many of them treated me to the same amazing bite!  By the end of my trip the sides of several of my fingers were black-and-blue with bruises from the repeated biting.

To give you a reference for what Evening Grosbeaks use their beaks for when they are not biting banders, they can sometimes be seen eating Chokecherry (Prunus virginiana) or Bitter Cherry (Prunus emarginata).  Like domestic cherry we all buy in the grocery store, these wild cherries have a very hard pit surrounded by a layer of soft fleshy meat.  Evening Grosbeaks carefully peel off the fleshy meat and then drop it on the ground.  They then take the hard pit in their beaks and crack it open to eat the tissue inside!  No wonder my fingers hurt!

Finding this our for my self, and watching others who have worked with me find it out for themselves, has actually been a very exciting process.  The only way to learn about a thing is to get close to it.  Sometimes this may mean closer than is comfortable, but it is only through this closeness, this intimacy, that true understanding is gained.  As my research on these birds continues, I am looking forward to learning many more little facts about them, and so to coming ever closer to true understanding.

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Songs and Calls

The vocalizations of birds can be divided into two broad categories: songs and calls (Catchpole and Slater 1995).  Songs tend to be complex, usually multisyllabic, often musical, and are generally learned by young individuals from adults that they hear and imitate.  They are used in territory establishment and defense, mate attraction, and to discourage potential rivals.  Calls tend to be structurally simpler, often monosyllabic, and have historically been thought to develop innately.  Calls are given in a wide range of contexts, but most calls can be placed into one of several categories: alarm call, contact call, roosting call, food call, begging call, or agonistic call (Marler 2004).  With the wide range of information that can be transmitted, studies of calls have taught us a great deal about communication and social structure in avian populations.  However, calls have historically been the focus of much less intense study than songs, and there is much that remains to be learned.  The diversity in repertoire, the levels of species specificity in particular calls and how this level changes with the category of call and the context in which it is given, and the selective pressures on both the call sender and receiver are all areas that warrant further and more detailed investigation.

Functions and Structure of Different Calls

Alarm Calls – Alarm calls can be divided into three subcategories – flee alarm, assembly alarm, and alert calls; calls in these subcategories tend to elicit different responses (Bradbury and Vehrencamp 1998).  The flee alarm is a signal sent to nearby individuals and tends to cause receivers to move rapidly away from the sender and/or to seek cover.  In many species, this signal can vary depending on the type of threat detected (aerial predator vs. terrestrial predator for example) and also on the proximity of the predator (Leavesley and Magrath 2005).  White-browed Scrubwrens (Sericornis frontalis) have been shown to increase the number of elements in their flee call with proximity of a suddenly appearing predator, and flee calls with larger numbers of elements also prompted more urgent responses in receivers (Leavesley and Magrath 2005).  Distress calls are an extreme form of flee alarm usually only given when an individual finds itself severely threatened.  These calls are loud, usually include a harsh rasping or screaming quality, and are often repeated rapidly.  Some evidence suggests that birds may give a distress call, when it is being attacked by a predator, to attract other predators with the result being that the new predator will compete with, and possibly drive off the current predator and so allow the prey to escape in the confusion (Koenig et al. 1991).  In some species the distress call attracts other members of the same species, and sometimes members of other species as well, that may then attempt to drive off the predator (Chu 2001, pers. obs.).

The assembly alarm (often calls a “mobbing call”, Bradbury and Vehrencamp 1998) is typically produced when a predator is located, causing receivers that are more widely dispersed to move toward the sender.  The information that is conveyed by these calls can not only include the location of the sender, but the location and type of threat as well.  This was demonstrated by Templeton et al. (2005), where presentation experiments revealed that Black-capped Chickadees (Poecile atricapilla) varied their mobbing calls, and their responses to these calls, in response to predator body size.

Calls that fall somewhere between the extremes of flee alarms and assembly alarms are alert calls.  These signals do not tend to cause receivers to move.  They are hypothesizes to inform other individuals of possible threats or other changes in the local environment (Seyfarth et al. 1980).  They may also be used to tell predators that they have been detected causing the predator to hunt other, less vigilant, prey (Caro 1995).  Studies suggest that when a local prey population has been alerted to the presents of a predator, the predator is less likely to succeed in its attempts to capture prey (Bergstrom and Lachmann 2001, Zuberbühler et al. 2009).

Each of these categories of alarm call can contain multiple distinct vocalizations.  Heterospecifics may also perceive and respond to these calls (Hurd 1996, Nolan and Lucas 2009).  For different species to correctly interpret a signal, that signal must have certain characteristics that cause it to be recognized by a wide and varying group.  Such characteristics may include relatively low variability and/or acoustic characteristics that are common to many species.  An example of common characteristics is given by Jurisevic and Sanderson (1994) who found that of the 30 species of bird examined, representing a wide range of taxa, 29 of them produced an alarm call with broad frequency range and a noisy or harmonic structure.  These calls do differ in area of active space, the area over which a call can be detected (Brenowitz 1982).  Flee calls are sent when danger is immediate and received by individuals that are close by (Magrath et al 2007).  Both of these conditions encourage the sender to vocalize relatively quietly and so improve the odds of the sender avoiding detection.  Distress calls are an exception to this in that they are loud, harsh sounds that may cause a predator to startle and stop the attack (Laiolo et al 2004, pers. obs.).  Assembly calls, contrastingly, attract individuals from some distance away, and so need to be louder than standard flee calls (Johnson et al 2003).  They must easily localizable using binaural cues or provide information about the location of the sender in order to effectively elicit a mob (Templeton et al. 2005).

Contact Calls – Contact calls are used by individuals of both sexes throughout the year and are thought to facilitate group cohesion, keeping group members in acoustic and/or visual contact.  They have a wide range of variation depending on the distance between the individual and the rest of the group and also depending on who is separated from whom.  They can be unique to individuals, allowing specific communication between particular individuals (Dooling et al. 1992, Bradbury 2003).  Contact calls may provide information to receivers about the approximate distance and activity level of the sender (Dooling et al. 1992).  The sound characteristics of, and response to, these calls are generally species specific (Wanker and Fischer 2001, Sharp and Hatchwell 2005).

Flight calls are a special form of contact call.  These calls are given while a flock is preparing to take flight and also during flights, and are hypothesizes to signal and coordinate group movements.  Flight calls are given by both sexes throughout the year, but are usually much louder than most other contact calls.  They can also be used to identify group membership and individual identity.  Mundinger (1970) found that female American Goldfinches (Carduelis tristis) could discriminate between the flight calls of their mate and those of other males.  Balsby and Bradbury (2009) found that Orange-fronted Conures (Aratinga canicularis) used their ‘chee’ call when two flocks were approaching one another to orchestrate flock fission or fusion.

Individual discrimination requires that a particular bird gives their own variant of a call with consistency in at least some acoustic features so as not to be confused with other individuals (Berg et al. 2010).  It also necessitates a wide range in variation across the whole population to allow for so many discrete variant to exist in acoustic space (Wanker and Fischer 2001).

Roosting Calls – Many species of bird vocalize as they are settling into night roosts.  Some tend to be sent over short distances such as a female calling her young to where she has settled for the night (Collias and Joos 1953).  Others tend to be sent over larger distances such as in a large flock of birds, like those observed in blackbirds or crows which gather together in the evening at a roost site (Hill and Lein 1985).  It is thought that members of these large flocks can gain information about local resources by how the flock breaks up each morning (Ward and Zahavi 1973, Buckley 1996, Dall 2002).  In this way, roosting calls serve as a way for individuals to locate flocks and so be in a position to benefit from the flocks’ collective knowledge the next morning.

Food Calls – Food calls are produced when the sender locates a food source (Elgar 1986, Buitron and Nuechterlein 1993), and may function to advertise a food find to receivers.  Senders may benefit for producing these calls, since receivers are typically young or close relatives of the sender, or potential mates (Buitron and Nuechterlein 1993).  For example, male domestic chickens are more likely to give food calls when there is another chicken nearby than when they are alone (Evans and Marler 1994), indicating that the calls have a communication function and are not simply a response to food.  Food calls are also more common when the nearby chicken is female which indicates the use of food calls in courtship (Marler et al 1991).  Some males have been observed to give food calls when holding a non-food item such as a stick, but only when the female is some distance away.  These males seem to be attempting to deceive the female with a false attractant which can only be detected as such with close proximity (Gyger and Marler 1988).    For food calls to be effective, therefore, the sender must be locatable and must be identifiable to individual; locatable so that the other birds can determine where the food source is, and identifiable to individual so that they can possibly assess the trustworthiness of the sender (Gyger and Marler 1988).  Birds outside of Galliformes rarely produce food calls and when they do occur it is usually around an extremely abundant food source (Elgar 1986, Heinrich 1989, Brown et al. 1991, Mahurin and Freeberg 2009).

Begging Calls – Begging calls are given most commonly by young to adults to elicit feeding (Godfrey 1991).  To be effective, adults must be able to locate and identify their own young.  In solitarily nesting species adults do discriminate between individual nestlings (Redondo and De Reyna 1988), but they have no need of discriminating between their own young and those of a different adult because when they return to the area of their nest, their own young are the only young present.  However, in colony nesting species, the task for an adult to correctly identify its own offspring out of a group of nests or young birds becomes much more challenging.  Beecher (1989, 1990) showed that individual nestling Barn Swallows (Hirundo rustica), which nest apart from one another, have much less stereotypy in their begging calls than do nestling Bank Swallows (Riparia riparia), which nest colonially.  Beecher argued that each Bank Swallow nestling must produce its own particular begging call variation very consistently so as not to overlap with its neighbors.  However, as a whole, a Bank Swallow colony will have many more begging call variants than a comparable number of solitarily nesting Barn Swallows, which can have overlapping begging call from nest to nest.  These studies serve to illustrate how the amount of variation, in terms of acoustic properties of a call in acoustic space, within an individual is related to how close the nearest neighbor is in terms of the same acoustic space.  Birds that have many other individuals close by must be very specific in the calls they give to avoid being confused with their neighbors, whereas bird that has no close neighbors is not so constrained.

Agonistic Calls – Aggressive behavioral interactions frequently include vocalizations, referred to as agonistic calls.  These calls can be given at any time of year, and are typically used to drive off, or decide the fighting ability and/or vigor of, the receiver.  Receivers can be other individuals of the same species, other species of bird, or even non-avian intruders.  These calls are usually harsh sounds and have a fairly large degree of variability, are usually given at close range, and do not contain information on the location of the sender (Black and Owen 2004).

Cited Literature

Balsby, T.J.S. and Bradbury, J.W., 2009. Vocal matching by orange-fronted conures (Aratingacanicularis). Behavioral Processes 82, 133-139.

Beecher, M.D., 1989. Signaling systems for individual recognition: An information theory approach. Animal Behavior 38, 248-261.

Beecher, M.D., 1990. “The evolution of parent-offspring recognition in swallows.”  In: Contemporary Issues in Comparative Psychology. Dewsbury, D. Sinauer Associates, Sunderland, MA.

Berg, K.S., Delgado, S., Okawa, R., Beissinger, S.R., and Bradbury, J.W. 2010. Contact calls are used for individual mate recognition in free-ranging green-rumped parrotlets, Forpus passerinus. Animal Behaviour 81, 241-248.

Bergstrom, C.T. and Lachmann, M. 2001. Alarm calls as costly signals of antipredator vigilance: the watchful babbler game. Animal Behaviour 61, 55-543.

Black, J.M. and Owen, M. 2004. Agonistic behavior in barnacle goose flocks: assessment, investment and reproductive success. Animal Behaviour 37, 199-209.

Bradbury, J.W. 2003. “Vocal communication in wild parrots.” In: Animal Social Complexity: Intelligence, Culture and Individualized Societies. DeWaal, F.B.M. and Tyack, P.L. Harvard University Press, Cambridge, MA.

Bradbury, J.W. and Vehrencamp, S.L. 1998. Principales of animal communication. Sinauer Associates, Sunderland, MA.

Brenowitz, E.A. 1982. The active space of red-winged blackbird song. Journal of Comparative Physiology 147, 511-522.

Brown, C.R., Brown, M.B., and Shaffer, M.L. 1991. Food-sharing signals among socially foraging cliff swallows. Animal Behaviour 42, 551-564.

Buckley, N.J. 1996. Food finding and the influence of information, local enhancement, and communal roosting on foraging success of North American vultures. Auk 113, 473-488.

Buitron, D. and Nuechterlein, G.L. 1993. Parent-young vocal communication in eared grebes. Behaviour 127, 1-20.

Caro, T.M. 1995. Pursuit-deterrence revisited. Trends in Ecology and Evolution 10, 500-503.

Catchpole, C.K. and Slater, P.J.B. 1995.Bird song: biological themes and variations. Cambridge University Press, Cambridge, MA.

Chu, M. 2001. Heterospecific responces to scream calls and vocal mimicry by phainopepla (Phainopeplanitens) in distress. Behaviour 138,775-787.

Collias, N.E. and Joos, M. 1953. The spectrographic analysis of sound signals of the domestic fowl. Behaviour 5, 175-188.

Dall, S.R.X. 2002. Can information sharing explain recruitment to food from communal roosts? Behavioral Ecology 13, 42-51.

Dooling, R.J., Brown, S.D., Klump, G.M., and Okanoya, K. 1992. Auditory perception of conspecific and heterospecific vocalizations in birds: evidence for special processes. Journal of Comparative Psychology 106, 20-28.

Elgar, M.A. 1986. House sparrows establish foraging flocks by giving chirrup calls in the resource is divisible. Animal Behaviour 34, 169-174.

Evans, C.S. and Marler, P. 1994. Food calling and audience effect in male chickens, Gallus gallus: their relationships to food availability, courtship and social facilitation. Animal Behaviour 47, 1159-1170.

Godfrey, H.C.J. 1991. Signaling of need by offspring to their parents. Nature 352, 328-330.

Gyger, M. and Marler, P. 1988. Food calling in the domestic fowl, Gallus gallus: the role of external referents and deception. Animal Behaviour 36, 358-365.

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Hill, B.G. and Lein, M.R. 1985. The non-song vocal repertoire of the white-crowned sparrow. Condor 87, 327-335.

Hurd, C.R. 1996. Interspecific attraction to the mobbing calls of black-capped chickadees (Parusatricapillus). Behavioral Ecology and Sociobiology 38, 287-292.

Johnson, F.R., McNaughton, E.J., Shelley, C.D., and Blumstein, D.T. 2003. Mechanisms of heterospecific recognition in avian mobbing calls. Australian Journal of Zoology 51, 577-585.

Jurisevic, M.A. and Sanderson, K.J. 1994. Alarm vocalizations in Australian birds: convergent characteristics and phylogenetic differences. Emu 94, 69-77.

Koenig, W.D., Stanback, M.T., Hooge, P.N., and Mumme, R.L. 1991. Distress calls in the acorn woodpecker. Condor 93, 637-643.

Laiolo, P., Tella, J.L., Carrete, M., Serrano, D., and Lopez, G. 2004. Distress calls may honestly signal bird quality to predators. Proc. R. Soc. Lond. B (Suppl.) 271,S513-S515.

Leavesley, A.J. and Magrath, R.D. 2005.Communicating about danger: urgency alarm calling in a bird. Animal Behaviour 70, 365-373.

Magrath, R.D., Pitcher, B.J., and Gardner, J.L. 2007. A mutual understanding? Interspecific responses by birds to each other’s aerial alarm calls. Behavioral Ecology 18, 944-951.

Mahurin, E.J. and Freeberg, T.M. 2009. Chick-a-dee call variation in Carolina chickadees and recruiting flockmates to food. Behavioral Ecology 20, 111-116.

Marlar, P. 2004.“Bird calls: a cornucopia for communication.” In: Nature’s Music: the science of birdsong. P. Marler and H. Slabbekoorn, Elsevier Academic Press, New York, NY.

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Mundinger, P.C., 1970. Vocal imitation and individual recognition of finch calls. Science 168, 480-482.

Nolan, M.T. and Lucas, J.R. 2009. Asymmetries in mobbing behaviors and correlated intensity during predator mobbing by nuthatches, chickadees and titmice. Animal Behaviour 77, 1137-1146.

Redondo, T. and De Reyna, L.A. 1988.Locatability of begging calls in nestling altricial birds. Animal Behaviour 36, 653-661.

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Sharp, S.P. and Hatchwell, B.J. 2005. Individuality in the contact calls of cooperatively breeding long-tailed tits (Aegithalos caudatus). Behaviour 142, 1559-1575.

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I came across my first family group of Bushtits of the year, today.  The group was comprised of what looked like three adults, which were probably the mated pair and one nest helper, and four young birds.  Bushtits are one of a number of species that include nest helpers in their reproductive strategy.  These helpers are usually young from the previous year that return to aid their parents.  Young birds that fledge from a nest early in the year also sometimes stay to act as helpers as their parents raise a second brood of young.  Since this family group that I found is so early I would not be surprised if the adults attempted a second brood.

A number of ideas about why young birds help raise their siblings are floating around.  One is that the young birds are getting valuable experience in raising babies, so that they will have better success when they do eventually go off by themselves.  Another idea is that the baby birds grow faster, and so fledge earlier, when there are more helpers to feed them.  A related idea has to do with what is called inclusive fitness.  This hypothesis says that the more individuals that carry a copy of a particular gene, the better, so helping relatives survive is actually a good strategy for preserving your own genes.  This is especially true if the individuals in question are close relatives, such as siblings, because there is a lot of shared genetic information.  A further idea is that good nesting territories are few and far between, so the helpers return to their parents territory and stay around in the hope of inheriting that nesting territory if and when their parents die or breed elsewhere.  This seems particularly possible in cavity nesting birds for which cavities have been shown to be a limiting factor in reproduction.  All these hypotheses seem reasonable, and they are not necessarily mutually exclusive, but few have been really well examined!  This seems to be an area that is ripe for some observations and experiments that might yield really interesting results.

So, who wants to put up a bunch of bird boxes and see what happens?

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