High-pitched Calls Research Articles

The Secret Superpower of Moths: Sound-Absorbing Stealth Camouflage

Today’s military aircraft typically use highly engineered “stealth” coatings that make them almost invisible to radar. Nature might seem an unlikely place to find such advanced technology, but one should never underestimate the ingenuity of evolution—moths developed their own form of stealth cloaking over 60 million years ago! That is before humans even walked the Earth! We discovered that the tiny scales on moth wings, which form fine dust when touched, provide stealth camouflage against the sonar used by their most dangerous foes—bats. By absorbing bats’ high-pitched calls, moths become nearly invisible to bats. Such stealth camouflage is a true superpower, as the coating on moth wings is light enough to allow flight, while still absorbing all the sounds bats make. The moths’ trick is that scales of various shapes work together to create a powerful super-absorber that is now inspiring humans to develop new sound-absorbing materials of our own.

Acoustic allometry, background stream noise and its relationship with large-bodied and voiceless rheophilic frogs

Anurans that breed in rivers and cascade streams need to deal with the influence of the low-frequency water flow noise that could interfere with their acoustic communication. To overcome that, some species display visual signals or emit high-pitched calls. However, there is a constraint related to body size [snout-vent length (SVL)] that limits the anurans' calling frequency range. Thus, to evaluate if water noise influences this allometric relationship, we analysed hylodid frogs’ SVL, dominant frequencies of advertisement call, and background noise to which individuals are submitted. Although Hylodes and Crossodactylus have differences in morphology and natural history, we found negative acoustic allometry in both genera. This allometry may be part of the explanation of the absence of advertisement calls in Megaelosia and Phantasmarana genera. Based on the large body lengths of Megaelosia and Phantasmarana species, if they could call, it would be low-pitched and acoustically masked by the stream noise. Besides, we found a positive relationship between Hylodes phyllodes advertisement call and background sound pressure level (SPL), thus, the analysed individuals, emitted louder calls when submitted to louder background SPLs. This study exemplifies the complexity of acoustic allometry in rheophilic species: we evidenced a strategy for intraspecific communication effectiveness in rivers and streams with broad water flow background noise; and how acoustic allometry coped with background noise could be implying in unexpected trait evolution, as lack of vocalization in anurans.

The Role of Acoustics in the Conservation of the Ivory-Billed Woodpecker (Campephilus principalis)

The Ivory-billed Woodpecker (Campephilus principalis) is an iconic species that has survived in barely detectable numbers for the past 100 years, during which it has been feared extinct only to be rediscovered several times. The most recent rediscovery was announced in an article that was featured on the cover of Science in 2005. The persistence of the Ivory-billed Woodpecker became controversial when ornithologists were unable to obtain a clear photo for documenting this ultra-elusive bird during multi-year searches at sites in Arkansas and Florida, where they had several sightings and were convinced these birds were present. Audio recordings of ‘kent’ calls and double knocks were obtained at both sites, but such recordings are not regarded as conclusive evidence of persistence. A debate on this issue that took place in Science and Nature focused on relatively weak video evidence obtained in Arkansas but excluded three videos obtained in Louisiana and Florida that show flights, field marks, and other behaviors and characteristics that are consistent with the Ivory-billed Woodpecker but no other species of the region. Kent calls were recorded in the 1930s, when other types of vocalizations were observed but not recorded, including a high-pitched alarm call. On two occasions in Louisiana, high-pitched calls were observed coming from the direction of an alarmed Ivory-billed Woodpecker, and several of them were recorded. The spectrograms of the high-pitched calls and all other known and putative vocalizations of the Ivory-billed Woodpecker consist of simultaneously excited harmonics. A harmonic oscillator model has been used to draw a connection between the drumming that is typical of most woodpeckers and the double knocks of the Ivory-billed Woodpecker and other Campephilus woodpeckers. Drumming corresponds to periodic forcing; double knocks correspond to impulsive forcing, and a single thrust of the body is sufficient to produce two impacts of the bill in rapid succession. The audio recordings from Arkansas and Florida were obtained with single microphones. A horizontal array of microphones would make it possible to detect weaker sounds and determine the directions of sources. This approach has the potential to lead to the discovery of a nest, and it might be more effective if the array is placed above the treetops, where sounds might propagate to longer ranges.

Advertisement calls of Limnonectes macrognathus (Anura: Dicroglossidae) and Leptobrachium smithi (Anura: Megophryidae), native frog species from Langkawi, Kedah, Peninsular Malaysia

ABSTRACT Bioacoustics information is an essential tool for anuran identification, especially within cryptic species. Here we recorded and analysed 17 calls of a male Limnonectes macrognathus individual and 15 calls of a single male Leptobrachium smithi. A Limnonectes macrognathus individual was caught at Gunung Raya on 13 July 2019, and an individual of male Leptobrachium smithi was caught at Lubuk Semilang on 18 January 2019. These species are native of the Langkawi Archipelago. The calls of Limnonectes macrognathus are short trills while Leptobrachium smithi calls have a single high-pitched ‘Kwak’ call. The advertisement call of Limnonectes macrognathus consists of two types that are emitted at a rate of 1 to 4 calls per minute. Each call lasts for 28.18 ± 29.69 (8.45–131.08) seconds (means ± SD (minimum – maximum)). Leptobrachium smithi produced high-pitched calls which consist of an apparent ‘KWAK’ sound. The advertisement call of Leptobrachium smithi consists of a single-note which is emitted 4–6 times per minute. Each call lasts for 0.22 ± 0.01 (0.21–0.23) seconds.

Call rate, fundamental frequency, and syntax determine male-call attractiveness in blue petrels Halobaena caerulea

In blue petrels (Halobaena caerulea), females are supposed to be particularly choosy and mate choice can take a couple of years. In these lifelong monogamous seabirds, choosing a good mate is crucial and has a strong influence on their fitness. Due to their nocturnal habits, the absence of sexual dimorphism, and the physical barrier between males calling from their burrow and females flying above the colony, vocal signals seem to be one of the main channels for males to communicate with potential mates. In a previous study, we investigated whether acoustic parameters of male calls carry information about morphological characteristics that might be indicators of males’ qualities. Here, we experimentally test whether these acoustic parameters linked to male characteristics are actually attractive to females. To do so, we played back modified calls of males to females in a colony of blue petrels of the Kerguelen archipelago. We found that flying females were more attracted by high-pitched calls, and by calls broadcasted at a high call rate. Previous studies showed a relationship between pitch and bill depth and length. In filter-feeding birds, such as blue petrels, bill morphology influences feeding efficiency. A high call rate is an indicator of sexual motivation and makes the caller easier to locate by potential mates and predators in the hubbub of the colony. We thus hypothesized that producing frequent high-pitched calls appeared to be preferable for a conspicuous sexual signaling although it may increase predation risks. Mate selection process is largely unknown in burrowing petrels due to their cryptic life at the colony. Here, we examined the implication of vocal signals in mate choice in the blue petrel Halobaena caerulea. We used an experimental setting based on a two-choice test to show that male calls are sexual signals attracting females. As expected, broadcasting male calls attracted females. Despite the apparent stereotypy of male calls, their acoustic parameters transmit pieces of information that may influence females’ preference. We found that females are more attracted by high call rate and high-pitched calls. This is the first evidence of the implication and influence of vocal signals in mate choice in burrowing petrels.

Allometric escape and acoustic signal features facilitate high-frequency communication in an endemic Chinese primate

The principle of acoustic allometry-the larger the animal, the lower its calls' fundamental frequency-is generally observed across terrestrial mammals. Moreover, according to the Acoustic Adaptation Hypothesis, open habitats favor the propagation of high-frequency calls compared to habitats with complex vegetational structures. We carried out playback experiments in which the calls of the Guizhou snub-nosed monkey (Rhinopithecus brelichi) were used as stimuli in sound attenuation and degradation experiments to test the hypothesis that propagation of Guizhou snub-nosed monkey calls is favored above vs through the forest floor vegetation. We found that low-pitched Guizhou snub-nosed monkey vocalizations suffered less attenuation than its high-pitched calls. Guizhou snub-nosed monkeys were observed emitting high-pitched calls from 1.5 to 5.0m above the ground. The use of high-pitched calls from these heights coupled with the concomitant behavior of moving about above the understory may provide a signal for receivers which maximizes potential transmission and efficacy. Our results support the Acoustic Adaptation Hypothesis and suggest that by uncoupling its vocal output from its size, this monkey can produce a high-pitched call with a broad spectral bandwidth, thereby increasing both its saliency and the frequency range over which the animal may more effectively communicate in its natural habitat.

Great roundleaf bats coordinate noseleaf and ear gyrations

![Graphic][1] Listening for the returning sound of your own echoing voice is always entertaining, but the echoes produced by cruising bats are more than a simple amusement. Guiding the nocturnal creatures past obstacles, the tiny mammals’ high-pitched calls also allow them to pinpoint tasty

Behavioural responses to cow-calf separation: The effect of nutritional dependence

There is increasing interest in keeping dairy cows with their calves during the milk feeding period, and in reducing distress associated with separation. The aim of this study was to investigate how nutritional dependence upon the cow’s milk affects behavioural responses to separation by both the cow and calf. For the first six weeks of life, dependent (n = 10) and semi-dependent (n = 10) calves could suckle from their mother at night, but semi-dependent calves also had ad libitum access to an automated milk feeder (AMF). Independent (n = 10) calves had ad libitum access to an AMF, and their dams wore udder nets to prevent nursing. Once cow and calf were separated, (first a 4 d period of partial separation with fence-line contact followed by total separation when the dam was removed), all calves had ad libitum access to the AMF. We used live, focal-animal observations and classified vocalizations either as high pitched (open mouth) or low pitched (closed mouth). We found that during partial and total separation, independent calves produced fewer high-pitched vocalizations/d than did dependent and semi-dependent calves combined (median: 0.00 vs. 7.2; U = 12.0, z = −3.21, P = 0.001 and 0.00 vs. 0.00; U = 40.5, z = −2.25, P = 0.024 for the two phases respectively) and also tended to produce fewer low-pitched vocalizations during partial separation (0.00 vs. 1.17; U = 29.5, z = −1.90, P = 0.057). Similarly, independent cows tended to produce fewer high-pitched calls during partial separation (0.00 vs. 1.08; U = 31.5, −1.74, P = 0.083) as compared to semi-dependent and dependent cows combined. During the separation phases, 23 calves (four, nine and ten calves) of dependent, semi-dependent and independent treatments, respectively, consumed at least 1.5 L/d from the AMF; these calves spent more time playing (s) (total separation; 3.67 vs. 0.00; U = 28, z = −1.99, P = 0.047) and less time close to the separation barrier (partial separation; 51.31-81.01-124.44 vs. 134.03-147.23-280.10), produced fewer high-pitched vocalizations during partial separation (0.00 vs. 8.33; U = 16, z = −2.22, P = 0.027), and tended to produce fewer low-pitched vocalizations (0.00 vs. 0.83; U = 21.5, z = −1.73, P = 0.083), than did calves consuming less milk from the AMF. The number of high-pitched vocalizations produced was negatively correlated with the calf’s milk intake (partial separation; Spearman’s r = −0.770, P < 0.001). The results indicate that nutritional independence from the dam reduces behavioural responses to separation.

Impact of prenatal stress and environmental enrichment prior to weaning on activity and social behaviour of piglets (Sus scrofa)

Prenatal stress (PNS) can have detrimental effects on behaviour and welfare, such as decreased exploration. Whether housing enrichment before weaning compensate negative effect of PNS in commercial pigs is unknown. To address this question, 44 sows were assigned to either a mixing stress (T) or a control (C) treatment in mid-gestation. During lactation, half of the T and C sows were housed with their 12-piglets litter in straw enriched pens (E) while the others were housed in standard farrowing crates (S). At weaning, 6 piglets per litter were selected and moved to non-enriched standard pens. Lying down, exploration and social behaviour were recorded in the home-pen before weaning (d 6, d 12, d 20), on the day of weaning (d 21), and after weaning (d 22, d 27) using scan and one-zero samplings. Three piglets per litter were individually subjected to a social isolation test and a social confrontation test at d 17. Data were analysed by day using mixed models with PNS, housing enrichment and their interaction as fixed effects. We found no interaction between the treatments, suggesting the absence of a compensatory effect of enrichment on PNS. Pre-weaning enrichment promoted exploration (P<0.004) and seemed to improve comfort, as piglets spent more time lying down (P<0.02), but was associated with reduced locomotion and play fighting (P<0.03) compared to no enrichment. After weaning, E piglets explored less (P<0.01) and played less (locomotion and fighting play: P<0.0003) than S piglets. They also performed more belly-nosing at d 27 (P=0.04). These results support the idea that the removal of enrichment at weaning negatively affects piglets. The E piglets exhibited higher emotional reactivity than S piglets (i.e. more high-pitched calls and escape attempts) during the social isolation test, but no clear effect was observed during the confrontation test. The effects of prenatal stress on behaviour were only apparent after weaning. On d 27, T piglets spent more time lying (P=0.02), and showed reduced exploration (P=0.004), locomotion play (P=0.03), fighting play (P=0.04) and mounting behaviour (P=0.002) than C piglets. In conclusion, both prenatal stress and pre-weaning enrichment affected piglet behaviour, but a compensatory effect of enrichment on the negative effects of prenatal stress could not be demonstrated.

Bats: a world of science and mystery

There are more than 1,300 species of bats - or almost a quarter of the world's mammal species. But before you shrink in fear from these furry of the night, consider the bat's fundamental role in our ecosystem. A single brown can eat several thousand insects in a night. Bats also pollinate and disperse the seeds for many of the plants we love, from bananas to mangoes and figs. Bats: A World of Science and Mystery presents these fascinating nocturnal creatures in a new light. Lush, full-color photographs portray bats in flight, feeding, and mating in views that show them in exceptional detail. The photos also take the reader into the roosts of bats, from caves and mines to the tents some bats build out of leaves. A comprehensive guide to what scientists know about the world of bats, the book begins with a look at bats' origins and evolution. The book goes on to address a host of questions related to flight, diet, habitat, reproduction, and social structure: Why do some bats live alone and others in large colonies? When do bats reproduce and care for their young? How has the ability to fly - unique among mammals - influenced bats' mating behavior? A chapter on biosonar, or echolocation, takes readers through the system of high-pitched calls bats emit to navigate and catch prey. More than half of the world's species are either in decline or already considered endangered, and the book concludes with suggestions for what we can do to protect these species for future generations to benefit from and enjoy. From the tiny bumblebee bat - the world's smallest mammal - to the Giant Golden-Crowned Flying Fox, whose wingspan exceeds five feet, A Battery of Bats presents a panoramic view of one of the world's most fascinating yet least-understood species.

Gender Identification by Calls and Body Size of the Streaked Shearwater Examined by CHD Genes

Like most seabirds Streaked Shearwaters Calonectris leucomelas have sexually monomorphic plumage. Researchers have conveniently identified gender in the field by means of two types of calls, associated with dimorphism in body size. By molecular sexing analysis using the chromo-helicase-DNA-binding (CHD) genes, we determined the gender of Streaked Shearwaters in relation to call types and body size. We recorded the type of calls, measured body dimensions and collected non-invasive samples (buccal cells or feathers) of Streaked Shearwaters at two breeding islands. As obvious amplification to identify gender by polymerase chain reaction (PCR) could not be obtained at high rates using a known universal primer pair, we developed two new primer pairs to identify gender in this species; this enabled us to identify the gender of all of the samples. Without exception all males gave high-pitched calls, whereas all females gave low-pitched calls. Molecular evidence also confirmed morphometric differences between males and females. We, therefore, conclude that Streaked Shearwaters exhibit sexual dimorphism in body size and call type. Males are significantly larger than females, and males give high calls whereas females give low calls.

Nestling use of alternative acoustic antipredator responses is related to immune condition and social context

Birds present a variety of antipredator responses, including the use of acoustic signals that may be directed to other individuals or to the predator. We tested competing hypotheses regarding antipredator responses by analysing patterns of variation in the use of distress calls in campo flicker, Colaptes campestris campestris, nestlings. More specifically, we tested whether immune response and social context (presence or absence of other individuals of the social group) were associated with variation in use of acoustic signals in response to human handling. Individuals with higher immunocompetence used proportionally more harsh, low-pitched calls (‘scream’ notes) than individuals with lower immunocompetence, while the latter used mostly tonal, high-pitched calls (‘week’ notes); in both cases there was no influence of the social context on call type. Individuals responded to the social context by giving fewer scream notes and week notes in the presence of adults of the social group than when the adults were absent. Although playbacks are necessary to determine the function of the calls, our results indicate that campo flicker nestling antipredator calls could be used to attract other individuals of the group to help defend the nestling. Also, the use of proportionally more scream notes by healthier individuals suggests that these notes could act as an honest signal of the nestlings’ physiological condition.

Calling by Domestic Piglets during Simulated Crushing and Isolation: A Signal of Need?

This study examined whether piglet distress vocalizations vary with age, body weight and health status, according to the predictions of the honest signalling of need evolutionary model. Vocalizations were recorded during manual squeezing (a simulation of being crushed by mother sow) and during isolation on Days 1 and 7 after birth in piglets from 15 litters. We predicted that during squeezing, younger, lighter and sick piglets would call more intensely because they are in higher risk of dying during crushing and therefore they benefit more from the sow’s reaction to intensive vocalization. For isolation, we predicted that lighter and younger piglets would call more because they are more vulnerable to adverse effects of the separation. Calls were analyzed in their time and frequency domain. The rate of calling, call duration, proportion of high-pitched calls and eight acoustic parameters characterizing frequency distribution and tonality were used as indicators of acoustic signalling intensity. Piglets that experienced “squeezing” on Day 1 produced more intense acoustic distress signalling than on Day 7. Lighter piglets called more during squeezing than heavier piglets. Health status did not significantly affect any of the indicators of intensity of vocalization during squeezing. In isolation, none of the parameters of vocalization intensity were affected either by the age or by the weight of the piglets. In summary, the model of honest signalling of need was confirmed in the squeezed situation, but not in the isolation situation.

The anatomy of vocal divergence in North American Elk and European red deer.

Loud and frequent vocalizations play an important role in courtship behavior in Cervus species. European red deer (Cervus elaphus) produce low-pitched calls, whereas North American elk (Cervus canadensis) produce high-pitched calls, which is remarkable for one of the biggest land mammals. Both species engage their vocal organs in elaborate maneuvers but the precise mechanism is unknown. Vocal organs were compared by macroscopic and microscopic dissection. The larynx is sexually dimorphic in red deer but not in elk. The laryngeal lumen is more constricted in elk, and narrows further during ontogeny. Several elements of the hyoid skeleton and two of four vocal tract segments are longer in red deer than in elk allowing greater vocal tract expansion and elongation. We conclude that elk submit the larynx and vocal tract to much higher tension than red deer, whereby, enormously stressed vocal folds of reduced effective length create a high resistance glottal source. The narrow, high impedance laryngeal vestibulum matches glottal and vocal tract impedance allowing maximum power transfer. In red deer longer and relaxed vocal folds create a less resistant glottal source and a wider vestibulum matches the low glottal impedance to the vocal tract, thereby also ensuring maximum power transfer.

The alarm call system of wild black-fronted titi monkeys, Callicebus nigrifrons

Upon encountering predators, many animals produce specific vocalisations that alert others and sometimes dissuade the predators from hunting. Callicebus monkeys are known for their large vocal repertoire, but little is known about the function and meaning of most call types. We recorded a large number of natural predator responses from five different groups of black-fronted titi monkeys in their Atlantic forest habitat in South Eastern Brazil. When detecting predatory threats, adult group members responded with call sequences that initially consisted of two brief, high-pitched calls with distinct frequency contours. Call A was mainly given to raptors but also to predatory capuchin monkeys and other threats within the canopy, while call B was given to predatory or non-predatory disturbances on the ground. In later parts of the sequences, we also recorded a high-pitched unmodulated call C and various low-pitched loud calls. Results therefore suggest that calls A and B provide listeners with rapid and reliable information about the general classes of danger experienced by the caller, while obtaining more specific information through other call types and combinations and behavioural responses. We discuss these findings in relation to current evolutionary theory of primate communication.

Putative audio recordings of the Ivory-billed Woodpecker (Campephilus principalis)

Putative audio recordings of the Ivory-billed Woodpecker (Campephilus principalis) are presented along with discussions of the videos from which they were extracted and the observations that were made when these data were obtained. On two occasions, high-pitched calls were heard coming from the direction of a bird that was identified in the field as an Ivory-billed Woodpecker. These calls seem to match the description of an alarm call that was reported in the 1930s. One of the videos captured a series of the high-pitched calls, which sound similar to the Blue Jay (Cyanocitta cristata) bell call but do not match published sonograms of that call. A putative double knock, which is characteristic of the Ivory-billed Woodpecker, was captured in another video a little over a minute before a large bird with characteristics consistent with an Ivory-billed Woodpecker flew into view. Since it is extremely difficult to observe this critically endangered species, information on audio clues could have an impact on its conservation.

Animals in translation: why there is meaning (but probably no message) in animal communication

Birds present a variety of antipredator responses, including the use of acoustic signals that may be directed to other individuals or to the predator. We tested competing hypotheses regarding antipredator responses by analysing patterns of variation in the use of distress calls in campo flicker, Colaptes campestris campestris, nestlings. More specifically, we tested whether immune response and social context (presence or absence of other individuals of the social group) were associated with variation in use of acoustic signals in response to human handling. Individuals with higher immunocompetence used proportionally more harsh, low-pitched calls (‘scream’ notes) than individuals with lower immunocompetence, while the latter used mostly tonal, high-pitched calls (‘week’ notes); in both cases there was no influence of the social context on call type. Individuals responded to the social context by giving fewer scream notes and week notes in the presence of adults of the social group than when the adults were absent. Although playbacks are necessary to determine the function of the calls, our results indicate that campo flicker nestling antipredator calls could be used to attract other individuals of the group to help defend the nestling. Also, the use of proportionally more scream notes by healthier individuals suggests that these notes could act as an honest signal of the nestlings' physiological condition.

Display behaviour of Shelley's Oliveback Nesocharis shelleyi

Bull ABC Vol 17 No 1 (2010) – 97 T olivebacks Nesocharis are a trio of Central and West African finches (Estrildidae) characterised by their distinctive grey, black and olive plumage (Fry & Keith 2004). Shelley’s Oliveback N. shelleyi is a range-restricted endemic of the Cameroon Mountains Endemic Bird Area, which straddles Cameroon, Nigeria and Equatorial Guinea (Stattersfield et al. 1998). Little is known concerning its behaviour or breeding (Goodwin 1982, Fry & Keith 2004), and its nuptial displays are undescribed. On 7 March 2009 I was observing birds on the Race Track above Buea, Mt Cameroon, with a group of nine other birders. At 14.00 hrs, at 1,700 m, I heard high-pitched calls emanating from c.4 m above the ground, directly above the trail. The source proved to be a male Shelley’s Oliveback, distinguished from the female by its having an olive breast and whitish borders to the sides of the black head (Fig. 2). In its bill it held, by the very tip, an upside-down grass stalk with seeds, c.15 cm in length. During c.3 minutes of observation it hopped back and forth along a bare branch, singing as it did so. Some of the time its flank feathers were expanded. This is similar to the observed behaviour of a singing male Whitecollared Oliveback N. ansorgei, its sister species, which sang from a branch 10 m above the ground, with its flank feathers expanded and its head and bill raised (Chapin 1959). Eighty seconds of song were recorded in .wav format (using an Edirol R09 recorder with a Sennheiser MKE400 microphone). Recordings were inspected using Raven Lite software (Cornell Lab of Ornithology 2003–08) and a sonogram produced (Fig. 1). The song consisted of a repeated series of 4–8 different, high-pitched, buzzy trills, in the 5–8 kHz range. Within each series, trills differed in duration, pitch and structure, some having an upward or downward inflection, and others being flat. Pitch appeared to undulate between successive notes, and different trills were repeated in a similar sequence, giving the song quite a musical tone. During 80 seconds, the sequence was repeated 14 times, lasting a mean 5.7 seconds.

First Confirmed Record of Breeding Brown Creepers in the Northwest Territories, Canada

The Brown Creeper (Certhia americana) is a small, bark-foraging songbird found throughout the forested regions from Central America north to south-central Canada and Alaska. Its avoidance of edges, cryptic plumage, and highpitched songs and calls contribute to a low detection rate for this species on most surveys (Hejl and others 2002; Alberta Sustainable Resource Development 2003). The abundance and distribution of the species at the northern edge of its range is poorly understood and is likely currently underestimated (Hejl and others 2002; Alberta Sustainable Resource Development 2003). Although creepers are known to occur along the Pacific coast to south-central Alaska, no confirmed breeding records have been reported above 606N latitude east of the continental divide (Hejl and others 2002). In this note, we document the 1st known occurrences of breeding Brown Creepers in the Northwest Territories, Canada. We observed breeding activity at 2 Brown Creeper territories within 100 m of point-count stations initiated for long-term forest songbird monitoring by the Canadian Wildlife Service (CWS) in the Liard Valley of the Northwest Territories. The study area for regional songbird monitoring spans over 700 km, and includes over 195 point-count stations and several line transects and census routes (Machtans and Latour 2003). The Liard Valley is in the far southwest corner of the Northwest Territories, just north of the British Columbia border and east of the Yukon border. Our observations were made in the low relief boreal forest region east of the Liard River. The Liard Valley typically has higher average temperatures and more precipitation than many regions of the northern boreal forest (Machtans and Latour 2003). Forests are typically old and, on average, taller than in other areas of the Northwest Territories. Vegetation and site characteristics for the Liard Valley are described in Machtans (2000) and Machtans and Latour (2003). From 15 June to 12 July 2008, several observations of Brown Creepers were made at 2 locations near Fort Liard, Northwest Territories (606139N, 1236229W) that confirmed breeding by this species in the area. On 15 June 2008, 2 Brown Creepers were heard and observed foraging during point-count surveys in the area (UTM Zone 10: 480493E 6697423N, NAD1983; hereafter location A). Upon further investigation, at least 3 juvenile creepers were flushed from the trunk of a tree, which provoked distraction displays from one or both parents. This display consisted of several aggressive flights to within 2 m of the observer’s head. On 21 June 2008, an audio recording of a singing Brown Creeper was obtained using a high quality hand held digital recorder (Edirol R-09, Roland Corporation) near the same location. On 6 July 2008, at least 4 Brown Creepers were foraging approximately 300 m from the original location. Several pictures were taken of the birds observed on 6 July (Fig. 1). On 12 July 2008, these birds were again observed and an inactive nest was found near the original sighting at location A (Fig. 2). The nest was 5.5 m above the ground in a 35-m-tall Trembling Aspen (Populus tremuloides) snag with a diameter at breast height (dbh) of 39 cm. On 15 June 2008, a Brown Creeper was heard and observed for about 10 min during a pointcount survey at a location approximately 4.6 km away from location A (UTM Zone 10: 480601E 6692793N, NAD1983; hereafter location B). On NORTHWESTERN NATURALIST 90:156–159 AUTUMN 2009 156 NORTHWESTERN NATURALIST 90(2)

Signals of need in a cooperatively breeding mammal with mobile offspring

In many bird species with biparental care for young in the nest, hungry chicks beg repeatedly and parents adjust their feeding rate to the call rate of young. Repetitive calling also occurs in fledglings and in some mammals where offspring follow provisioners. It is not yet clear whether, in mobile systems with dispersed young where adults cannot compare the vocal behaviour of all young simultaneously, the calls represent a signal of need. We investigated repetitive begging by cooperatively reared meerkat, Suricata suricatta, pups that foraged with the group. Pups produced two types of begging calls: repeat calls over long periods and high-pitched calls mainly confined to feeding events. Food-deprived pups stayed closer to feeders, and begged for longer and more intensely by calling at a higher rate. Hungry pups increased both the rate of repeat calls, which were given continually, and the number of high-pitched bouts, but adults increased their food allocation only in relation to the rate of repeat calls. Our study indicates that hunger may lead to several changes in vocal behaviour, only some of which may be used by adults to assess need.