Risk allocation: acute and chronic predator exposure have contrasting effects on Song Sparrow (Melospiza melodia) singing behaviour
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Abstract:
Increasing the danger posed by predators may cause prey animals to alter their behaviour. For example, they may be more vigilant and so feed more slowly. Breeding male Song Sparrows (Melospiza melodia (A. Wilson, 1810)) spend much time in conspicuous, loud song, which is an important behaviour for territorial defense and for mate attraction. We measured their singing behaviour in relation to both chronic (active Cooper’s Hawk (Accipiter cooperii (Bonaparte, 1828)) nest nearby) and acute (playback of hawk calls) predator exposure. We found that proximity to a Cooper’s Hawk nest had little or no influence. In contrast, the response to acute exposure was strong and immediate: Song Sparrows reduced the song rate and the proportion of time spent singing, lowered perch height, and increased concealment. The decline in the amount of song during the few minutes following playback attributable to the acute exposure was 34.6%. We analyze these results in light of theories about how animals adjust risk taking in response to predation danger. Given that the numbers of their predators have risen steadily for the past few decades and affect the level of singing, we consider the implications for trend estimates of songbird populations based on surveys using auditory methods.Keywords:
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Emberizidae
Emberizidae
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Journal Article Songs of the Fox Sparrow. I. Structure of Song and Its Comparison with Song in Other Emberizidae Get access Dennis J. Martin Dennis J. Martin Department of Biology, Pacific Lutheran University, Tacoma, Washington 98447 Search for other works by this author on: Oxford Academic Google Scholar The Condor, Volume 79, Issue 2, 1 April 1977, Pages 209–221, https://doi.org/10.2307/1367164 Published: 01 April 1977 Article history Accepted: 25 June 1976 Published: 01 April 1977
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Expanding our understanding of signal complexity in animals could start with thevery smallest songbirds. Black-capped Chickadees (Poecile atricapillus) can encodevery specific details about a threat in their acoustically simple alarm calls. Can othersmall songbird species, such as the Song sparrow (Melospiza melodia), encode thatsame level of detail in their even simpler alarms? Furthermore, is it possible for them tointerpret those details, and are those details reliable? I measured the response of Songsparrows to the suggestion of a threat (two recordings of Song sparrow alarms, one inwhich the call elements were played much faster than a normal call and one in whichthey were played much slower) then, separately, to the threat itself (a taxadermic mountof an Eastern screech owl, Megascops asio), and then to a non-threating control (aNorthern bobwhite, Colinus virginianus). The Song sparrows consistently approachedthe speaker more closely when they heard a faster alarm call and also produced afaster alarm call in response to the more threatening screech owl mount. This suggeststhat there is specific data encoded in the alarms and that they will produce a differentalarm according to the perceived threat level of what they are encountering.
Emberizidae
Alarm signal
Songbird
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A habituation test paradigm was used to examine the responses of free-living territorial adult male song sparrows (Melospiza melodia) to a range of synthetic songs. The three-phrased test songs differed from one another in having either conspecific or heterospecific (swamp sparrow, M. georgiana) syllables, or silence, in the second phrase. Subjects were exposed to repeated presentations of one song type until their approach distance to a loudspeaker increased. In one experiment, birds were habituated with a song consisting of three phrases of song sparrow syllables and then tested for generalization to either novel song sparrow syllables in the second phrase, swamp sparrow syllables, or silence. Birds discriminated between song sparrow syllables on two response measures, and between song sparrow and swamp sparrow syllables on one measure. In a second experiment, after habituation to a song with swamp sparrow syllables in the second phrase, birds did not generalize to novel song sparrow syllables, but they did generalize to novel swamp sparrow syllables. Thus song sparrows make finer distinctions among conspecific syllable variants than with alien syllables. The results further suggest that subtle species-specific differences in note structure within syllables are discriminated by song sparrows and potentially provide an adequate basis for individual recognition by song.
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Swamp
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We compared the pronounced geographic pattern in the recolonization of Britain by the Eurasian Sparrowhawk (Accipiter nisus) from 1970 onward with the spatiotemporal pattern among House Sparrow (Passer domesticus) populations over the same period, using data on the occurrence of both species at garden feeding stations. Using a simulation of House Sparrow population trends based on a logistic model that incorporated a predation index derived from Eurasian Sparrowhawk incidence functions, we generated a close approximation to the unique trajectories among House Sparrow populations in rural and urban sites in different regions of Britain. We carried out further comparisons using two contrasting methods that focused solely on temporal patterns. We used estimates of the varying date of Eurasian Sparrowhawk recolonization at different sites to derive time variables in relation to recolonization date. One such relative time variable proved to be a better predictor of House Sparrow numbers than chronological time; it indicated that House Sparrow numbers were generally stable or increasing prior to recolonization by Eurasian Sparrowhawks but declined continuously afterward. We also detected a significantly greater decrease in House Sparrow numbers when Eurasian Sparrowhawks were present using a method that compared annual changes in the abundance of prey species in the presence or absence of a predator. On the basis of these results, we argue that predation by Eurasian Sparrowhawks may be a sufficient explanation for the decline in House Sparrows in Britain. We also argue that urban House Sparrow populations' long-term release from predator pressure made them especially vulnerable when urban habitats were colonized by Eurasian Sparrowhawks.
Accipiter
Passer
Accipitridae
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Songbird
Emberizidae
Bunting
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Cryptic behaviour is a common example of a passive defence in animals enabling prey to reduce the likelihood of being detected by a predator (e.g.Edmunds 1974).One such common behaviour enabling birds to be cryptic is freezing behaviour, which is commonly exhibited by birds in response to the presence of a predator (Slater 1999).A striking example of freezing behaviour in Tree Sparrows Passer montanus was observed at Tovetorp Zoological Research Station in south-eastern Sweden on 28 February 2002.I observed a Sparrowhawk Accipiter nisus launching an attack, at 14.45 in the afternoon, towards a feeding station located underneath a birch tree where Great Tits Parus major, Blue Tits P. caeruleus, Tree Sparrows and Greenfinches Carduelis chloris where foraging.The Sparrowhawk attack was not successful, and as a result all birds at the feeder escaped apart from one Tree Sparrow.Tits and Tree Sparrows escaped towards protective cover approximately ten meters away whereas the Greenfinches escaped into midair and perched in a birch tree some distance away.After the unsuccessful attack the Sparrowhawk perched in the birch approximately two meters above ground well within the branches keeping it quite concealed, and only three meters away the remaining Tree Sparrow stayed on top of one of the feeders.The Tree Sparrow started to freeze when it detected the Sparrowhawk, and it remained motionless in a crouching position holding the body in a horizontal stance.Ten minutes later, at 14.55, the first bird, a Great Tit, made the first approach towards the feeder.When the tit was flying towards the feeder the Sparrowhawk took off and
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Passer
Beak
Nest box
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During the last 30 years, there have been marked declines in the populations of many British songbirds breeding on farmland, while two of their main predators, sparrowhawk (Accipiter nisus) and magpie (Pica pica), have spread back into areas from which they had disappeared. The causes of the songbird declines remain unclear but given the coincidence in timing, it might appear that increased predation could be responsible. Although many studies have failed to find links between changes in the populations of breeding songbirds and mortality from avian predators, previous work has, with few exceptions, involved only short–term studies on small spatial scales. Here we use large–scale, long–term data from a national bird census scheme to examine whether magpies and sparrowhawks could have depressed the rates of year–to–year population change in 23 songbird species. Our results indicate that magpies and sparrowhawks are unlikely to have caused the songbird declines because patterns of year–to–year population change did not differ between sites with and without these predators.
Accipiter
Songbird
Accipitridae
Breeding bird survey
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Emberizidae
White (mutation)
Canto
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Here we show how a migratory songbird, the chipping sparrow (Spizella passerina), achieves prompt and precise vocal imitation. Juvenile chipping sparrow males develop five to seven potential precursor songs; the normal development of these songs requires intact hearing but not imitation from external models. The potential precursor songs conform with general species-typical song parameters but differ from the song of wild, adult territorial males. As chipping sparrow males return from migration to start their first breeding season, they settle close to an older adult. The young male then stops producing all but one of its precursor songs, retaining the one that most resembles that of its neighbor. This single song then becomes more variable and, in a matter of days, is altered to closely match the neighbor's song. This elegant solution ensures species specificity and promptness of imitation.
Songbird
Vocal Learning
Emberizidae
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