Posts Tagged ‘Vocalizations’

For the past few days, a fledgling Western Scrub Jay has been hanging out in the bottlebrush just outside my office window. It has been pretty fun to watch this bird get used to the world at large.

A lot of time is spent screeching for its parents who make frequent visits to the bottlebrush to deliver food items. I can always tell when one parent is getting close because the screeching gets much louder and more intense as the parent approaches. Both adults visit this bush a lot, and I have not seen them take food anywhere else, so I suspect this youngster outside my window is their only fledgling this year. Hearing the screeching over even this short period of time has been interesting because the bird has been getting better at it. Each day, this young jay is sounding less and less like a young and inexperienced bird, and more and more like a normal, adult Western Scrub Jay. It is cool to be able to actually hear the practice paying off.

While it waits for it parents to bring it food, the young bird with its greyer and fluffier feathers, spends a good bit of time jumping from branch to branch within the bush. It has a bit of an obstacle course set up for itself as it bounces around and around in circles all covered by the protective foliage of the plant. As it moves around, it does some practice flapping and a lot of very precise movements as it improves it fine motor control. It also is practicing hunting. When it sees an insect or other potential prey in or around the bush, it jumps after it and attempts to catch it. It is sometimes successful, but usually these successes are made against pretty easy to catch animals. It did really well catching a snail.

It and I did have one funny interaction. Most of the time, I am sitting at my desk and the bird does not seem aware of me at all. At one point, however, it saw something on the glass or at the edge of the window and flew right to it perching on one of the small dividers between panes of glass. When it landed, clinging with just the tips of its toes rather awkwardly it pauses a moment and looked through the glass and into the room. That is when it saw me and was very surprised indeed! Whatever brought it over to the window in the first place was forgotten as the jay jumped right back into the bottlebrush. It certainly learned that there are humans in the world!

Hopefully, this young bird continues to improve its skills and makes it through its first winter (the hardest part of a birds life) and can teach its own young some of the valuable lessons it is learning.

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A few days ago, I found myself in Blackwood Canyon on the west coast of Lake Tahoe. It is a beautiful spot where Evening Grosbeaks have been reported regularly over the last couple of weeks. The day was lovely, and the birding was terrific with lots of classic mountain birds all around. Warbling Vireos and Hermit Warblers were foraging in the poplars that grow along side the stream that runs down the middle of the canyon. MacGillivray’s and Wilson’s Warblers were leading young birds around through the willows. Spotted Sandpipers were walking and bobbing their tails as they foraged along the rocky stream edges. Female Mallards lead broods of ducklings from pool to pool.

I did find a flock of Evening Grosbeaks, though they were not particularly cooperative in terms of my research plans. However, while I did not get the experimental trials I had hoped for accomplished, I did see something new and cool. I was stopped along the side of a road at around 9:30am beside a small group of spruce tree when I heard an Evening Grosbeak giving really loud flight calls. They were actually kind of spectacularly loud! As I watched, I saw the grosbeak, a male, flying from tree top to tree top and continuing to give these high amplitude calls. After standing below him recording for a few minutes, I figured out why he was behaving this way. There was an adult Red-tailed Hawk perched in the top of one of the spruce trees and the grosbeak was mobbing it. Now, Evening Grosbeaks are known to use their flight calls to coordinate the movement of a flock and they are also used by birds to locate other individuals over long distances. Further, they may possibly play a role in mate choice decisions and in population identification. However, to the best of my knowledge, this is the first time flight call have been observed being used in a predator harassment context! After a few more minutes, the Red-tailed Hawk flew off. The Evening Grosbeak, having succeeded in annoying the predator into leaving, quieted down and then departed on his own business.

This was yet another reminder that calls can have many different functions even when it is basically the same call, and even when that call is has a fairly simple structure. What subtle differences communicate different information to a receiver? Was the volume of these calls an important component of harassing a predator? Are there other differences (speed of delivery, frequency range, something else) between flight calls that are used in different contexts? I have this one recording, and so will certainly examine it to see if there is anything that jumps out at me, but with only the one occurrence, it will be hard to identify smaller differences, even though such small differences may be quite important to the birds involved. This also served as a reminder that exciting things can happen, but you have to spend time out with your study subjects to see them!

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Vocalizations, like any other phenotypic trait, can change over time.  These changes can have several causes which can be generally divided into drift (the random accumulation of mutations that are generally neutral in terms of fitness) and selection (changes that are under some directional pressure and tend to increase fitness).  The forms of drift and selection fall into five major categories.  In any given population, these categories can act independently of one another, they can act in concert, or they can oppose each other.  The five categories are Cultural Drift, Genetic Drift, Cultural Selection, Natural Selection, and Sexual Selection.

Cultural Drift is the process where changes in vocalizations occur by chance.  These changes can come from imitation errors as young individuals attempt to copy the sounds produced by adults.  They can also arise in the form of innovations where an adult incorporates a new sound element into its vocalization.  The accumulation of these changes can eventually lead to the formation of new vocal types.

Genetic Drift is the random accumulation of mutations at loci that regulate sound production.  Ass these mutations accumulate, the physiological and mechanical abilities of an organism to make sounds may be altered.  Due to this, genetic drift is likely to have a greater effect on the evolution of vocalizations when the mutations happen to effect the limits of performance for an animal.

Cultural Selection occurs when there is differential propagation of vocalizations across generations.  This can occur in the form of vertical transmission from parents to offspring, horizontal transmission between peer groups or siblings, or oblique transmission from adults to unrelated young.  Unlike the following two mechanisms, cultural selection is not directly driven be fitness.  Instead, variations in vocalizations can spread through a population for other reasons.  One example is because of a dominant individual using one particular variation and not others.  Another example is when a particular frequency transmits through a habitat better than others, such as how low frequency sounds travel through dense foliage farther tan high frequency sounds.  This would lead more young individuals to be exposed to low frequency sounds and so learn to imitate them.

Natural Selection can influence vocalizations directly, because of some fitness benefit that a particular vocalizations give the signaler, or indirectly, by altering some physical structure that is used is sound production (changing bill morphology adapting to different seed sizes, for example).  The most commonly discussed role of natural selection in vocal evolution is through the process known as reinforcement.  Reinforcement is where two populations have diverged to the point where hybrids between the populations are less fit than pure bred members of either population.  This might be because the two populations have split to use foods of two different sizes.  A hybrid might not be good and consuming either food size, and so be less fit.  If such hybrid disadvantage exists, natural selection is expected to favor individuals of each population that tend to avoid mating with individuals of the other population.  Vocalizations are frequently the first from of contact that two individuals have, and so they are in a unique position to moderate interactions and will tend to evolve towards greater species-level specificity.

Sexual Selection can take the form of intersexual selection or intrasexual selection.  Intersexual selection can drive the evolution of vocalizations by the preferences of one sex (usually the female) for particular vocalizations of the other sex (usually the male), by sensory bias where one sex (usually the male) uses a vocalization that the other sex (usually the female) is predisposed to respond to, when a display can only be produced by individuals of high fitness, when the production of a display carries some fitness cost such as increased risk of predation, or when a vocal display can inform the receiver as to their likely genetic compatibility with the sender.  Intrasexual selection on vocalizations come ins the form of members of same sex (usually males) using vocalizations to compete with one another.  Here, the evolution of vocalizations can occur when vocalizations contain information about the sender.  This information can be in the form of the senders size, strength, willingness to fit, social status, etc.  Facets of vocalizations that are often favored include increased vocal complexity, high amplitude, low frequency, and high calling rate.

These mechanism for the evolution of vocalizations are most thoroughly studied in bird songs.  However, bird calls may be susceptible to all of these types of evolution as well.  This would be particularly true of calls that are learned, as opposed to innate, for which more and more examples are being discovered.

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One facet of my research on the Evening Grosbeak (Coccothraustes vespertinus) that I am hoping to put together is a much better survey of where the different flight call types occur, what they are doing, and what they are eating.  To give a bit of background, five different variants of Evening Grosbeak flight call have been observed.  These different variants have been labeled Type 1 through Type 5, and while the differences are subtle to the human ear, they are distinct enough that with practice they can be identified in the field.  They are also different enough that the grosbeaks themselves can almost certainly tell them apart as well, and so may play an important role in group membership identification.

The geographic ranges of birds that make these different flight call types has been generally worked out.  Type 1 is found mostly in the Pacific northwest and central Rocky Mountains, Type 2 is mostly found in the Sierra Nevada and southern Cascade Mountains of California and Oregon, Type 3 is mostly found around Great Lakes and in New England and southeast Canada, Type 4 is mostly found in the southern Rocky Mountains of Colorado and New Mexico, and Type 5 is mostly found in the mountains of central Mexico and southern Arizona.  I say mostly a lot in that description because there is a lot that we don’t know.  It is known that there is a fair bit of overlap in where the different flight call types have been observed.  In the Sierra, while most of the birds give Type 2 flight calls there are birds that give Type 1 flight call as well.  In Wyoming, where Type 1 would be expected, Type 1 birds are the most commonly observed, but Type 4 birds occur there in smaller numbers as well.  There are also parts of the continent where it is not well understood what type might be the most common.  The area in central Canada that is between Type 1 and Type 3 is filled with question marks.  Nevada and Utah are between the Type 1, Type 2 and Type 4 regions.  This area does not have a lot of Evening Grosbeak habitat, but it seems likely that these birds do occur on high mountain ridges.  They may or may not breed there, but even knowing what birds pass through the area would be interesting.  Another huge area of unknowns surrounds Type 5.  Very little research has been done on where these birds occur, exactly.  Even the portion of the range that is in the USA in Arizona and possibly New Mexico is not well established.

An even less understood aspect of Evening Grosbeak life is that of diet.  Most bird books give the very general “eats seeds and insects” with little or no explanation of what seeds and what insects.  Do birds that make different flight call types eat different foods in their respective different ranges?  No one knows.  When individuals that produce different flight call types find themselves in the same place, do they then retain any differences in diet, or do they all simply eat whatever is around?  Again, no one knows.

So here is my call for aid.  I want to collect information on the calls and diet of Evening Grosbeaks across North America.  This will take a very long time if I do it all myself, but I am hoping that you might be willing to help.  If you are willing to help there are two ways you can.  One is if you see Evening Grosbeaks any where, take a moment to observe what they are eating.  What I am looking for is information on what these birds are eating in the wild, so bird seed out of a feeder may not give the most interesting information, although you never know.  The second way to contribute is if you hear an Evening Grosbeak vocalizing.  If you do, and have any recording device (this does not have to be fancy, I have gotten useful recordings off the recorders in digital cameras), then make a recording.  These recordings will be best if they have the vocalizations of only one bird calling for as long as possible, but any recording will be useful and this includes birds at feeders.  After you have made an observation or recording make a note of the date, time of day, location (be as exact as possible.  GPS locations would be great), and any notes on behavior or habitat that seems interesting to you.  Then send them along to me at anhaiman@ucdavis.edu

This is going to be a long and slow accumulation of knowledge which is why I am starting now.  I will be collecting this information for years.  As you find birds and can pass the information along to me, don’t worry about being too late.  Thanks in advance!

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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).

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