The Auk A Quarterly Journalof Ornithology Vol. 116 No. 4 October 1999 The Auk 116(4):875-877, 1999 OVERVIEWS NEST ARCHITECTURE AND AVIAN SYSTEMATICS FREDERICK H. SHELDON •,3 AND DAVID W. WINKLER 2 •Museumof NaturalScience, 119 FosterHall, LouisianaState University, Baton Rouge, Louisiana 70803, USA; and 2Sectionof Ecologyand Systematics, Division of BiologicalSciences, Cornell University, Ithaca, New York 14853, USA ANYONEWHO TRIES to identify a bird nest, causeof geneticand selectiveconstraints on the withoutseeing the bird that constructedit, en- morphology and behaviors associatedwith tersthe realm of aviansystematics. The attempt nestbuilding (Winkler and Sheldon1994). In- to determinethe identity of the nestleads im- stead,they tended to be slightmodifications on mediatelyto an effort to categorizethe nestac- the main nestingtheme. For bird systematists, cordingto its overt features:Is it in a hole?Is who are scientistsinterested in understanding it on a branch? If the nest lies in a hole: Where evolutionarypatterns, this adaptivetinkering is thehole located? How big is it?How wasthe hasprovided invaluable clues to the historyof hole constructed? For the nest itself: What ma- avian life. It has createda hierarchyof nest terial is it made of? How is the material fitted typesthat, when deciphered, can shed light on together?How is the nestlined? thephylogenetic (genealogical) relationships of Such queststo identify nestsdepend ulti- birds, and it has left an evidential trail of the matelyupon evolution and the "nested"nature interactionbetween genetics and ecology,the of nest architecture.Members of a groupof driving forceof evolution.Thus, even a rudi- closelyrelated birds tend to build their nests mentaryconsideration of the possibleowners based on a common architectural theme, and of an unidentified nest delves into the methods subgroups "nested" genealogicallywithin and logic of avian systematicsand yields in- larger groupstend to build neststhat are var- sightsinto bird evolution. iationson the larger theme.By examininga An interestingexample of "nested" nest ar- nest,we canquickly assess the generaltype of chitecture that we have studied concerns swal- bird that constructedit (oriole,swallow) by the lows of the genus Hirundo and their allies basictheme (pendant nest, mud nest). Then, by (Winkler and Sheldon1993). This group in- followinga routeof subthemes(e.g. shape, lo- cludes Barn Swallow (Hirundo rustica), Cliff cation, constructionmethod, materials, etc.), Swallow (Petrochelidonpyrrhonota), Cave Swal- we canwhittle downthe list of possiblebuild- low (P.fulva), CommonHouse-Martin (Delichon ers.The reason for the"nesting" of nestthemes urbica),and about32 other species.All build is that throughoutevolutionary history, birds nests made of mud. The ancestral mud nest was havemet ecological challenges (e.g. changes in a simple cup-shapedstructure, like that of a climate,predation, and competition)by adapt- Barn Swallow. A more derived (modern) nest ing their neststo eachnew situation.These ad- from this groupis a slightlyenclosed cup, like aptationstended not to be revolutionary,be- that of a Common House-Martin. The most re- centlyevolved nests are ornate, enclosed globes E-mail: [email protected] and retorts,sometimes with longentrance tun- 875 876 Overviews [Auk, Vol. 116 nels, like thosemade by the New World Cliff shipsof groupsof organismsby identifyingde- Swallow and the "red-rumped" and "cliff" rived charactersthat are sharedamong group swallows of the Old World. The architecture of members (synapomorphies)and not shared thesemud nestsprovides strong clues to phy- with membersof othergroups. The reconstruc- logeneticrelationships of theseswallows. For tion of phylogenyfrom nest structure,there- example,all 15 speciesthat build simplemud fore, shouldbe simply a matter of coding ar- cups are membersof the same phylogenetic chitecturalcharacters and identifyingnatural group as the Barn Swallow.All speciesthat groupsby their synapomorphies.However, or- build retort-shapednests with entrancetun- nithologistsrarely do this, for severalreasons. nelsare members of the samegroup as the Cliff First, there are not enoughdata. This is espe- Swallow.Moreover, the pattern of increasing cially true for tropicalgroups of passerines,for complexityin nest structurethrough time, which many species'nests are undescribedor from simple cups to ornate retorts, corre- known from only a singleexample. To identify spondswith manyother aspects of the group's and code nest charactersrequires not only ecologyand behavior,including distribution, knowledgeof the nest,but somenotion of var- socialstructure, and breeding. iation in the characters; a character that varies Onemight think thatnest characters, as man- a greatdeal within a speciesis not likely to be ifestationsof behavior,are too plasticand un- helpful in phylogeneticwork. predictableto provide a useful guide to phy- Another problemin codingnest characters logeny and evolutionaryhistory. However,re- concernsa lack of independence.It arises,for cent studies have shown that behavioral char- example,when nestsbuilt in holes are com- acterscan be just as effectivein reconstructing paredwith nestsplaced on branches.Not only phylogeniesas are morphologicalor molecular do thesenest types sharea limited number of characters(e.g. de Queiroz and Wimberger characters because of fundamental differences 1993).The main problem with behavioralchar- in their site•, but some of the common charac- actersis not that they are unreliable,but that ters will be stronglyand jointly influencedby thereare usually not enoughof themto resolve the site;they will notbe independentindicators phylogeneticrelationships. Another problem is of phylogeneticrelationship. For example,ex- that most behavioral characters need to be ob- terior nestsare characterizedby specificattach- servedin the field and are subjectto a rangeof ment methods and greater camouflageand interpretationsby differentresearchers. In this strengththan interior nests.The interdepen- regard, nest characterstaken from museum dence of charactersassociated with attachment, specimenspresent a distinct advantage.Nests camouflage,and strengthwould not presenta can be lined up on a table and examinedthor- problemif the two typesof nestbuilders were oughlyby researchersand reviewers alike. This distinct phylogenetically.However, if some potential for scrutiny assuresgreater objectiv- hole-nestingspecies were moreclosely related ity and discussionin choosingand interpreting phylogeneticallyto branchnesters than to oth- nestcharacters than in usingother behavioral er hole nesters,phylogenetic analysis would characters. probablyfail. Unlessthe interdependenceof Nest structure has been used for centuries to nesting characterscan be controlled by a indicatebird relationships,but not in a rigor- weightingscheme (as commonlydone in mo- ous way. In the past, ornithologistsgrouped lecular phylogenetics),the hole nesterswould speciesbased on overall similarity of their appear as a group distinct from the branch nests.But similarityis difficultto quantifyand, nesters,and the phylogenywould be incorrect. worse,it can result from convergentevolution Giventhe pitfallsof nestcharacters, but also as well as commondescent. Many unrelated their great potential, Kristof Zyskowskiand speciesof birds,for example,have adapted con- Rick Prum have accepted,in this issueof The vergentlyto nest in tree holesbecause of the Auk,the ultimate challenge in nestanalysis: the protectionafforded by thesesites. Fortunately, reconstructionof ovenbirdphylogeny. Mem- the problemthat convergentevolution poses to bers of the ovenbirdfamily (Furnariidae)dis- phylogeneticshas been alleviated, to somede- play more variationin nestingbehavior than gree,by the developmentof cladisticanalysis. any other avian family, and becauseof their This method determines the "nested" relation- tropical distribution and diversity (240 spe- October1999] Overviews 877 cies),the furnariidsare oneof the mostpoorly Prumtree is largelyon the righttrack (also see understoodmajor groupsof birds in terms of Vaurie1971, 1980). Moreover, simply by virtue phylogeny,ecology, and behaviorThe large of its pioneeringnature, the Zyskowskiand number of speciesassures a problem with Prumstudy has moved avian systematics sub- missingdata, which Zyskowski and Prum have stantiallyforward. Amassing such a largeset of donemuch to remedy.Moreover, the remark- data and workingthrough the processof cod- ablevariation in nestarchitecture (e.g. self-ex- ing nestcharacters, in themselves,are substan- cavatedand adoptedholes, nests attached to tial achievements. We now have a foundation vertical and horizontal substrates,pendant not only for future work on the ovenbirds,but nests,domed nestsof vegetationor clay) also alsoa guide for use of nestcharacters in sys- raisesthe specterof at leasta poorlyresolved, tematicstudies of othergroups of birds. if notincorrect, phylogeny because of variation among nest types and resultant interdepen- LITERATURE CITED denceof characterswithin nesttypes. Finally, DE QUEIROZ•A., AND 19.H. WIMBERGER.1993. The Zyskowski and Prum have no substantive usefulnessof behaviorfor phylogenyestima- studymodels from whichto work. No modern tion: Levels of homoplasyin behavioral and workershave attempted to reconstructa phy- morphologicalcharacters. Evolution 47:46-60. logenyof a familyof birdsbased solely on nest- VAURIE,C. 1971. Classificationof the ovenbirds(Fur- ing characters,let alonea family of suchsize nariidae).H.