How Social Environment Affects Song in Phylloscopus Leaf Warblers

Introduction

In the breeding season, birds use song as a means of recognising and identifying the species and sex of the individual singing. They can then act accordingly, for example; if a breeding-age female bird hears a male’s (in most species it is just the males who sing) song, she can approach him with the intent of mating, or if a male hears another male’s song in his territory, he can choose to fight, sing back or flee. These are the fundamental purposes of bird song (Catchpole, 1995).

The Phylloscopus Leaf Warblers are a genus of small Old-World passerines. Most are migratory, especially those at higher latitudes. They mainly inhabit forests on both the breeding and wintering grounds and are insectivorous (Baker, 1997). Because many species in the genus are so similar in visual appearance, vocal communication is very important in interactions between individuals of the same species, so while there is a lot of variation in each species’ song, there are elements which stay constant and can be used to specifically identify an individual (Tietze et al., 2015).

Because birdsong is a means of social interaction, the fact that it can be flexible and alter in meaning with changes in the social environment is vital.

 

Section 1: How Social Environment Affects the Song of an Individual in the Short-term

It would be beneficial to a singing bird if it could change its song immediately because of changes in its social environment, this would allow it to convey information without risking injury and a waste of energy on physical actions (Falls, 1969).

In the Willow Warbler P.trochilus, male songs produced in agonistic situations with other males are markedly different to the ‘spontaneous’ songs produced in normal life. Agonistic songs are shorter in duration (x̅ = 2.32s compared to x̅ = 3.14s) and number of syllables (x̅ = 13.46 compared to x̅ = 19.34) than spontaneous songs. However, the volume and length of the songs increase over the period of the interaction. Immediately before physically attacking another male, the regularity of songs is lower than in normal life, but this then increases to above the normal regularity after the attack. There is also a song element, known as the A-syllable, which is rare in spontaneous songs but very frequent in agonistic songs (immediately before an attack, frequency = 0.80). It is uttered 3-5 times in the first half of the song and therefore completely changes the structure and conveys a very specific meaning to other Willow Warblers. This meaning is that the singer is going to attack (Jarvi et al., 1980).

Wood Warblers P.sibilatrix also change their songs in interactions with other males. In an experiment, Szymkowiak and Kuczyński (Szymkowiak and Kuczynski, 2017) found that birds increased the rate at which they sung by an average of 0.84 songs per minute during a simulated interaction with another ‘male’. This behaviour also correlated with the intensity of their aggressive response. Additionally, Szymkowiak and Kuczyński showed that males reacted more aggressively to playbacks with a higher song rate (this meant a faster approach to, more attacks on and more flyovers of a dummy)(Szymkowiak and Kuczynski, 2017).

Clearly, when a territorial male is approached by another male, leaf warblers often change their song to convey meaning. The changes that occur depend on species and the nature of the interaction (within a species). I have not found any reference to song changing in an interaction with a potential mate, but this could be because different vocalisations or behaviours other than true song have evolved for this purpose. Indeed, Simms (Simms, 1985) states that Willow Warblers have a ‘thin shrew-like note’ and a ‘plaintive cheep’, both uttered in display. They also have a well-developed and characteristic courtship display which involves a chase and wing-waving, although courtship behaviour is clearly quite variable as Simms (Simms, 1985) also says that there is sometimes a ‘little display flight with a burst of song’.

 

Section 2: How Social Environment Affects the Song of an Individual in the Long-term

Birds may also need to alter their song over the course of a breeding season or period in a breeding season because of prevailing conditions in their social environment. The primary cause of this is to increase their chances of mating.

Willow Warblers change their song in response to the density of the population they are residing in. Due to environmental factors and mortality of individuals in this migratory and philopatric species (Hedlund, 2017), density will change from year to year and even within a breeding season. In a study by Goretskaia (Goretskaia, 2004), birds spent a lower percentage of their time singing (median 58% compared to median 68%) during observation periods in the lower density population. It is worth noting that in the high density population, 51% of singing time comprised of duels with other males, whereas this percentage was only 7% in the low density population.  The structure of the songs were also different between the study areas, in the low density area, the median number of ‘similar elements per initial phrase’ was 3-4 in the low density area and 4-7 in the high density area. The difference remained significant when females were excluded from the analysis and Goretskaia concluded that the number of duels directly affects the length of the initial phrases of the song. In high density areas, the variability, which is most prevalent in duels, and the number of double-songs (two songs in one) also increased.

The social environment of a juvenile male Common Chiffchaff P.collybita during its first 44 days of living affects the song it sings for the rest of its life. When birds were hand-reared, and hence did not hear the songs of other males during the first 44 days of their life, their songs differed significantly from normal. But, when taken from the wild when the birds were 44-100 days old, and kept in acoustic isolation, there was not a significant change in their songs (Thielcke and Zimmer, 1986).

The breeding distribution Iberian Chiffchaff P.ibericus is normally restricted to Iberia and North Africa (Svensson, 2010) but, being a long-distance migrant on a north-south axis, they are prone to overshooting their breeding grounds and turning up well north of their normal distribution  (Pérez-Tris, 2010; Cottridge, 1997). I personally observed an extralimital vagrant Iberian Chiffchaff in Yorkshire singing the typical song of its species, a perfect copy of the song of Common Chiffchaff and intermediates between the two. This phenomenon is known as mixed-singing and is relatively frequent in areas where Iberian and Common Chiffchaffs, which are expanding their range and infilling areas previously occupied by Iberians, overlap in distribution (Dubois, 2008) and when Iberians occur as vagrants (Collinson, 2008). It is thought that when there is a shortage of potential mates of the same species, such as is occurring during vagrancy to areas where Common Chiffchaffs are present and in the areas of Common Chiffchaff distribution infilling, Iberian Chiffchaffs will incorporate elements of Common song, which they will be hearing from the Common Chiffchaffs inhabiting the area, into their own in an attempt to attract a female Common Chiffchaff and pass on their genes in a non-assortative mating system (Dubois, 2008). According to Thielcke (Thielcke, 1983), the phenomenon of new vocal traditions arising in areas of poor cultural transmission, such as in the dual situations of Iberian Chiffchaff, is one which can allow the creation of new dialects within a species which can then persist.

Mixed singing also occurs in Willow Warblers, which incorporate elements of Common Chiffchaff song into their own. It is becoming more frequent in Britain in line with the retreat of Willow Warblers from the south and east and the resultant infilling of the free Phylloscopus niche with Chiffchaffs. Willow Warblers can increase the complexity and variability of their song between their first and second years, probably using the songs of neighbouring territorial individuals as templates (Gil et al., 2001). Because Willow Warblers are philopatric (Hedlund, 2017) and, in the very closely related and similar Chiffchaff (Simms, 1985), the main period of song learning is within the first 44 days of life (Thielcke and Zimmer, 1986), the lack of singing Willow Warblers where juveniles are growing up could result in the juveniles incorporating Chiffchaff into their song because Chiffchaffs are the predominant perceived territorial competitor. This has an advantage in that the mixed song acts as a stronger deterrent to Chiffchaffs, which could be occupying potential Willow Warbler territory, and result in fewer costly physical conflicts (Lawn, 2018).

Seemingly, an evolutionary advantage exists for birds which are able to adapt their songs in the long term to the prevailing social environment, whether this is by sexual opportunism in an unfavourable social environment (Dubois, 2008), such as with Iberian Chiffchaffs, or adaptive territoriality in a species like the Willow Warbler (Lawn, 2018). On the other hand, learning of the song has been shown to be directly affected by the social environment (Thielcke and Zimmer, 1986).

 

Overall Conclusion

Ultimately, song changes as a result of the prevailing social environment because the singer has to adapt to manipulate the social environment to its own benefit; to convey meaning in individual interactions, to better defend territories and to increase the chances of attracting a female. Song change also occurs as a function of social environment in ways in which the singer cannot manipulate the social environment reciprocally and is necessarily required to change. Additionally, severe abnormalities in the social environment can directly affect song.

 

References

Baker, K. 1997. Warblers of Europe, Asia and North Africa. 1 ed. London: Christopher Helm.

Catchpole, C.K., Slater, P.J.B. 1995. Bird Song: Biological Themes and Variations. Cambridge: Cambridge University Press.

Collinson, J.M., Melling, T. 2008. Identification of vagrant Iberian Chiffchaffs – Pointers, pitfalls and problem birds. British Birds. 101(April), pp.174-188.

Cottridge, D., Vinicombe, K. 1997. Rare Birds of Britain and Ireland: A Photographic Record. London: Collins.

Dubois, P.J. 2008. Mixed-singing Iberian Chiffchaffs: is it their ‘swan song’? British Birds. 101(July), pp.379-380.

Falls, B.J. 1969. Functions of Territorial Song in the White-throated Sparrow. In: Hinde, R.A. ed. Bird Vocalizations.  London: Cambridge University Press, pp.207-232.

Gil, D., Cobb, J.L.S. and Slater, P.J.B. 2001. Song characteristics are age dependent in the willow warbler, Phylloscopus trochilus. Animal Behaviour. 62, pp.689-694.

Goretskaia, M. 2004. Song structure and singing behavior of Willow Warbler Phylloscopus trochilus acredula in populations of low and high density. Bioacoustics-the International Journal of Animal Sound and Its Recording – BIOACOUSTICS. 14, pp.183-195.

Hedlund, J.S.U., Sjoesten, Frida, Sokolovskis, Kristaps, Jakobsson, Sven. 2017. Point of no return – absence of returning birds in the otherwise philopatric willow warbler Phylloscopus trochilus. Journal of Avian Biology. 48(3), pp.399-406.

Jarvi, T., Radesater, T. and Jakobsson, S. 1980. THE SONG OF THE WILLOW WARBLER PHYLLOSCOPUS-TROCHILUS WITH SPECIAL REFERENCE TO SINGING BEHAVIOR IN AGONISTIC SITUATIONS. Ornis Scandinavica. 11(3), pp.236-242.

Lawn, M. 2018. Interspecific Territoriality by Mixed-singing and Song-switching Willow Warblers: a possible Case of Character Convergence. British Birds. 111(June), pp.339-348.

Pérez-Tris, J., Ramírez, Á., Tellería, J.L. 2010. Are Iberian Chiffchaffs Phylloscopus (collybita) brehmii long-distance migrants? An analysis of flight-related morphology. Bird Study. 50(2), pp.146-152.

Simms, E. 1985. British Warblers. London: William Collins Sons & Co Ltd.

Svensson, L., Mullarney, K., Zetterström,D., Grant, P.J., Christie, D.A. 2010. Collins Bird Guide: The Most Complete Guide to the Birds of Britain and Europe. London: HarperCollinsPublishers  Ltd.

Szymkowiak, J. and Kuczynski, L. 2017. Song rate as a signal of male aggressiveness during territorial contests in the wood warbler. Journal of Avian Biology. 48(2), pp.275-283.

Thielcke, G. 1983. Did dialects of the Chiffchaff Phylloscopus collybita develop through learning withdrawal? Journal of Ornithology. 124(4), pp.333-368.

Thielcke, G. and Zimmer, U. 1986. EARLY EXPERIENCE DETERMINES THE SONG OF THE CHIFFCHAFF (PHYLLOSCOPUS-COLLYBITA). Ethology. 73(3), pp.191-196.

Tietze, D.T., Martens, J., Fischer, B.S., Sun, Y.H., Klussmann-Kolb, A. and Packert, M. 2015. Evolution of leaf warbler songs (Aves: Phylloscopidae). Ecology and Evolution. 5(3), pp.781-798.

 

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High on Fritillaries

So, in late July I went to the Lake District with my family, and no matter how glorified it is compared with its biological value, Arnside still has good butterflies. Here are the Lepidopteran highlights of my trip.

Near to where we were staying these Purple Hairstreaks put on a great show one evening, but failed to appear subsequently. They adorned a small oak on a hillside, allowing spectacular views. This is the first time I have seen the purple properly.

 

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Purple Hairstreak

In the one nice day we had, I managed to get to Arnside Knott, hoping for some new butterflies.

The first of which I saw almost immediately; High Brown Fritillary.

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High Brown Fritillary

All but one of the frits I clinched turned out to be female High Browns, the other a male, which I found odd, considering Dark Green is much commoner country-wide and female butterflies are usually more retiring than males. Most were rocketing over the slopes, too fast to follow, but a pair seemed to favour a sheltered patch of Bracken.

My second new butterfly came just as we were leaving. I had gone to look on the other side of the knott for it when my mum called me and told me she thought she’d found it. I walked relatively casually back, thinking there was no chance of it still being there as well as being the target species.

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Northern Brown Argus

I was wrong.

I was a bit on the late side, as can be seen from the wear on this individual, but I knew there was a chance. Sometimes you get lucky with wildlife. I did miss a flyover Honey Buzzard, but let’s forget about that.

Fresh Scotch Arguses were a real treat too, having only seen battered individuals on my previous visit to the knott.

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Scotch Argus

The moth trapping was amazing at our cabin, my personal highlight was this Large Emerald.

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Large Emerald

30 Days Wild Pan-species Challenge: Final Day!

I’ve done it; I’ve had one pan-species lifer per day for the last month for 30 days wild. I started the month on 1437 species, and I end the month on 1546. Now, I know what your’re thinking, “That’s a gain of 109 species, not 30?!?!” Well, this increase includes all the times I had too many lifers to identify/blog about in one day, and it also includes identifications of species found in other months.

We started on an ant-lion and we end on yet another moth. This time a macro; this Small Yellow Wave which I found fluttering around a copse on the edge of my village, fortunately it settled long enough for a picture.

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Small Yellow Wave

I doesn’t look that yellow in this photo but is still a very pretty moth, quite a nice ender, at least its a macro!

 

30 Days Wild Pan-species Challenge: Day 29

Yet another moth. I do make a conscious effort to identify every moth which I don’t recognise, as I do with bees, so it makes sense that this series has been overloaded with them. Other groups are a lot easier to master.

Glyphipterix simpliciella made up today’s part of the moth lifer contingent. It was in the grassy meadow area of my local botanical gardens.

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The foodplant of this moth is the grass known as Cocksfoot, hence why its colloquial name is Cocksfoot Moth. Makes sense right?

I really like these sort of micros, they look like Grapholita and they just look clean.

30 Days Wild Pan-species Challenge: Day 28

I had a bit of a frantic search for a lifer when I got back from dipping the Bempton Black-browed Albatross, again… A Bonxie was a small compensation.

Here it is, in all its glory, the wondrous Worm Slug, Boettgerilla pallens.

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Worm Slug

I’m sure I’ve seen them before but this was the first time I’ve really confirmed it.

I’m glad this was the first time I’ve had to resort to rummaging around in my garden for slugs at quarter past nine at night for this challenge.

30 Days Wild Pan-species Challenge: Day 27

Rubbish weather today, but a slightly brighter patch prompted me to go out into the grassy alleyway behind by house and I found this diminutive but stunning Grapholita compositella, today’s lifer.

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Grapholita compositella

Grapholita are a great little group of moths with their blue-grey background colour and minimalist white detail, and compositella is distinctive in having the blotch covering the trailing edge of the forewings divided into 4 strips.

30 Days Wild Pan-species Challenge: Day 26

Crowle Moors was absoloutley heaving with insects today, I’m sure once I’ve identified them all there will be some rare ones/loads of things I’ve never seen before.

However, my overriding target was the Large Heath, a specialist of these lowland bogs. In previous years I have managed to miss this butterfly while my family saw it, don’t ask me how this happened!

Today was different, however and this time I came away victorious. In total, we saw at least five individuals, mainly feeding on thistle.

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Large Heath

The Large Heaths were a nightmare to photograph, they kept leaning and turning in weird angles, and the multitudes of Large Skippers, Meadow Browns and Ringlets wouldn’t share the thistle nicely.

There was quality in other taxonomic groups too, a female Adder making her way through tinder-dry vegetation and the distinctive songs of Tree Pipit, Cuckoo and a single Garden Warbler.

 

30 Days Wild Pan-species Challenge: Day 25

Today’s lifer was a nice hoverfly which goes by the name of Eupeodes corollae, a common species which lives in virtually every corner of the British Isles. I found it on a road verge near my village, it was feeding on an Umbellifer amongst a plethora of Episyrphus balteatus.

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Eupeodes corollae

It’s a prertty standard-looking hoverfly but they all count. I believe that the joined stripes on the abdomen are characteristic of this species.

 

30 Days Wild Pan-species Challenge: Day 23 and 24

Well, I did get my pan-species lifer yesterday, but I didn’t have time to blog about it. Have I failed my challenge? I think I’ve at least done enough to warrant carrying on.

Anyway, here’s yesterday’s lifer, a Rustic Shoulder-knot from the garden moth trap.

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Rustic Shoulder-knot

And today, whilst volunteering at RSPB Bempton Cliffs, I went to check out the Northern Marsh-orchids and I found this specimen which is literally days in not hours away from going over completely!

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Northern Marsh-orchid

I got that lifer by the skin of my teeth.

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Common Spotted x Northern Marsh-orchid?

I also saw this, which I think looks like Common Spotted x Northern Marsh, all of the orchids I saw on site resembled this bar the pure Northern Marsh mentioned earlier. It seemed darker than the photo shows but it could just be a very, very well-marked Common Spotted. I have indeed noticed that the strength of the spots on Common Spotted-orchids varies from site to site. Common Spotted x Northern Marsh has been seen on this site previously.

30 Days Wild Pan-species Challenge: Day 22

A bit of a conundrum today: I suspect this is Smicronyx jungermanniae, which would be a lifer, but I admittedly have no experience on whether this species needs microscopy or anything to confirm.

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It was on a fencepost in a grassy area on Flamborough Head, but it could have been blown from anywhere as it was quite windy today and I would be extremely grateful if someone could shed a bit of light on this for me.