Mamma knows best: why a generalisthummingbird selects the lessabundantmoss for nest building

FRANCISCO E. FONT �URBEL ,1,4 FELIPE OSORIO,2

VALENTINA RIFFO,3 MAURICIO NU ~NEZ,1 ROBERTO

BASTIAS1AND GAST�ON O. CARVALLO

1

Manuscript received 12 December 2019; revised 11 February2020; accepted 24 February 2020. Corresponding Editor: JohnPastor.

1Instituto de Biolog�ıa, Facultad de Ciencias, PontificiaUniversidad Cat�olica de Valpara�ıso, Valpara�ıso, Chile.

2Freelance consultant, Villarrica, Chile.3Departamento de Ciencias Ecol�ogicas, Facultad de Ciencias,

Universidad de Chile, Santiago, Chile.4E-mail: fonturbel@gmail.com

Citation: Font�urbel, F. E., F. Osorio, V. Riffo, M. Nu~nez, R.Bastias, and G. O. Carvallo. 2020. Mamma knows best: why ageneralist hummingbird selects the less abundant moss for nestbuilding. Ecology 101(7):e03045. 10.1002/ecy.3045

Many birds around the world use plant material tobuild nests that allow for hatching eggs and keeps chickssafe (Healy et al. 2015). Despite being a common phe-nomenon in nature, our knowledge of the mechanismsunderlying how and why specific plants are selected fornest building is somewhat limited. Hummingbirds(Trochilidae) in particular depend heavily on plant mate-rials to build their nests (Calvelo et al. 2006, Torres-Dowdall et al. 2007). Hummingbirds commonly usemosses as nesting material because mosses can retainmoisture for long periods and thereby prevent eggs fromdrying out (Breil and Moyle 1976, Blem and Blem1994). Also, mosses may have antimicrobial propertiesthat may enhance nestling survival (Basile et al. 1999,Alabrundzinska et al. 2003).Recently, we documented that the Green-backed Fire-

crown (Sephanoides sephaniodes Trochilidae), the south-ernmost hummingbird and main vertebrate pollinator ofaustral South America, actively selects particular materi-als during nest building (Osorio-Zu~niga et al. 2014).This hummingbird uses two kinds of plant materials tobuild their nests: scales or hairs of the fronds of the fernLophosoria quadripinnata to make the nest lining, andmosses to make the nest structure (Fig. 1). Among thosemosses, three species are the most common: Ancistrodesgenuflexa (present in 100% of the nests), Weymouthia

mollis (present in 27% of the nests), and Weymouthiacochlearifolia (present in 17% of the nests), whereas theremaining species are present occasionally, in low pro-portions, and usually in nests >1 yr old (Osorio-Zu~nigaet al. 2014). An intriguing pattern emerges when weexamine those nests in detail: A. genuflexa represents upto 97% of moss biomass in the nests, but it is particularlyscarce in the environment (constituting only 0.1% of thetotal moss biomass in the forest). Contrarily, W. mollisand W. cochlearifolia constitute only 3% of moss bio-mass in the nests despite being the most abundant spe-cies by far in the environment (constituting 94% of thetotal moss biomass in the forest). Therefore, an obviousquestion arises: why does S. sephaniodes actively selectof one of the least abundant moss species for nest build-ing and not the most abundant mosses? Active selectionof material for nest building has been associated with thepresence of secondary compounds in plants that acts asbiocides of pathogens and parasites (Clark and Mason1985, 1988, Pires et al. 2012) and these generally repre-sent a small, non-random proportion of plant speciesavailable in the environment (Clark and Mason 1985,1988, Pires et al. 2012, L�opez-Rull and Mac�ıas-Garcia2015). To elucidate a potential functional role of thosethree bryophytes as anti-pathogenic agents in nests, weassessed its chemical composition and antimicrobialactivity.We performed chemical analyses on those three moss

species (details are available in Appendix S1), finding 65compounds in total (43 of them extracted with methanoland 22 extracted with dichloromethane; Appendix S1:Fig. S1). From those, 14 compounds were found inA. genuflexa, 42 compounds in W. cochlearifolia, and 20compounds in W. mollis (Appendix S1: Table S1). Of thecompounds present, 64% were polar compounds inA. genuflexa, 45% in W. cochlearifolia, and 65% inW. mollis. The two Weymouthia species shared eightcompounds, whereas A. genuflexa shared only one com-pound with W. cochlearifolia and two compounds withW. mollis. Regarding the functions of those components(Appendix S1: Table S2), we found eight compounds inA. genuflexa with known functions (Asawaka et al.2013). Five of those compounds have antibacterial prop-erties (benzothiophene, undecyl acetate, farnesol, oleicacid, and (E,Z)-3,7,11-Trimethyl-2,6,10-dodecatrien-1-ol), one has antifungal properties (tetradecenol), andone is known to repel insects (8-methyl-6-nonenamide).It is noteworthy the presence of phthalic acid, known tobe toxic for mammals, which might be preventing nestpredation by small mammals, and particularly by thearboreal marsupial Dromiciops gliroides that feed oneggs of many native birds (Font�urbel et al. 2012). Exceptfor 8-methyl-6-nonenamide (an insect repellent), none of

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The Scientific NaturalistEcology, 101(7), 2020, e03045© 2020 by the Ecological Society of America

these compounds are present in any of the Weymouthiaspecies.Weymouthia cochlearifolia had 21 compounds with

known properties, 18 of them with antimicrobial proper-ties, one with antiviral properties (only one of them isalso present in A. genuflexa), one known to be insectrepellent and one known to be irritant to humans. Inturn, W. mollis had nine compounds with known prop-erties, seven with antimicrobial properties and two withantifungal properties (none of them present in A. genu-flexa). While we performed these analyses, we had sparemoss material stored at 4°C in the laboratory; bothWey-mouthia samples rot (attacked by fungi) after six monthswhile A. genuflexa samples remained intact for over ayear.Then, we used the moss extracts, obtained from the

three species using methanol and dichloromethane, toassess antimicrobial activity in laboratory conditions,against five common pathogenic bacteria. We per-formed the same procedure used only the solvents ascontrols. Those bacteria strains included some Enter-obacteriaceae (Escherichia coli and Salmonella enter-ica) and other common bacteria species (Pseudomonas

aeruginosa, Listeria monocytogenes, and Staphylococcusaureus). Our trials show that A. genuflexa has signifi-cant antimicrobial activity over the five bacteriastrains tested (Fig. 2). The extracts of A. genuflexawere particularly effective against E. coli as it presentsthe widest inhibition halo, and its growth is inhibitedwith the lowest extract concentration (Appendix S1:Tables S3 and S4). On the other hand, W. mollis andW. cochlearifolia showed no antimicrobial activity inany case (Fig. 2, Appendix S1: Tables S3 and S4).These results show that, despite the presence of somecompounds with a known antimicrobial activity pre-sent in both Weymouthia species, they are little effec-tive against these common pathogens. In contrast,those compounds present in A. genuflexa are highlyeffective instead. Interestingly, there are a few reportsof diseased hummingbirds that have been associatedwith bacteria of the family Enterobacteriaceae (Godoyet al. 2014), suggesting that they could be infected bythese type of pathogens.Due to its wide distribution range along southern

South America and its generalist behavior as a pollina-tor, responsible for pollinating ~20% of the native woody

FIG. 1. (a) The moss Ancistrodes genuflexa growing attached to a native tree (Oncol Park, October 2017; photo credit: FelipeOsorio), (b) the hummingbird Sephanoides sephaniodes (Vi~na del Mar botanical garden, June 2018; photo credit: Diego Reyes), and(c) S. sephaniodes nest with chicks inside (Senda Darwin scientific station, Chilo�e Island, June 2018; photo credit: Andr�es Char-rier).

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flora of the temperate Patagonian rainforests, we firstexpected S. sephaniodes to have a generalist-opportunisticbehavior related to the use of nest-building material.Later, we realized that material selection was far fromrandom, showing clear preferences towards a moss spe-cies that is particularly scarce (Osorio-Zu~niga et al.2014), but the reasons for such preference wereunknown. Our chemical and microbial analyses providea potential explanation for that: using A. genuflexainstead of the abundant Weymouthia species confersmore durability to the nest (which is highly relevant con-sidering that S. sephaniodes may reuse nests for multipleseasons). Therefore, A. genuflexa presence in the nestmight benefit the hummingbirds increasing their egg andchick survival by reducing the nest pathogens. Evenwhen the three moss species are structurally similar tothe naked (human) eye, they differ greatly in chemicalcomposition. As A. genuflexa contains mainly polarcompounds with antimicrobial properties, they are sol-uble in water. They can be active in the nesting materialat wet conditions, predominant in the temperate rain-forests of South America. Such a particular associationbetween S. sephaniodes and A. genuflexa could be theresult of the natural selection process, in which selectivehummingbirds actively searching for this moss havemore and healthier offspring than those that use nestingmaterials according to their availability in the environ-ment. The large cognitive abilities of S. sephaniodes andhummingbirds in general (Gonzalez-Gomez et al. 2015)could be responsible for developing such fine nestingmaterial selection behavior.We tend to label species as generalists or specialists,

assuming that they should act as is in every aspect oftheir lives. However, our results showed that a generalist

pollinator such as S. sephaniodes can otherwise be veryselective and act as a specialist in other aspects of theirlife history. Among those aspects, nest-building behaviorplays an important role, but remains little understood.Based on our results, future studies may explore special-ization patterns in nest building in other hummingbirdspecies, or even more generally in birds. We expect thatcareful nesting material selection will be favored by nat-ural selection, as it may substantially increase offspringsurvival. Also, we expect these selection patterns to showsignificant geographic variations, as a result of changesin the nesting materials available.

ACKNOWLEDGMENTS

We thank Oncol Park for granting access to the study site.We are grateful to Diego Reyes and Andr�es Charrier for thehummingbird and hummingbird nest pictures. FEF was sup-ported by CONICYT-FONDECYT project 11160152.

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C E C E C E

0

5

10

Comparison

Hal

o s

ize

(mm

)A. genuflexa W. cochlearifolia W. mollis

FIG. 2. Summary of the antimicrobial activity of mossextracts (from Ancistrodes genuflexa, Weymouthia mollis, andWeymouthia cochlearifolia) over five common bacteria strands.We compared halo size between control (C) and extract (E)essays in the laboratory. Error bars represent standard error.

July 2020 THE SCIENTIFIC NATURALIST Article e03045; page 3

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Additional supporting information may be found in the onlineversion of this article at http://onlinelibrary.wiley.com/doi/10.1002/ecy.3045/suppinfo

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