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Communication is an essential component of animal social systems and a diverse suite of signals can be found in the natural environment. An area of animal communication that, for technical reasons, we know very little about is the field of ‘movement-based’ or ‘dynamic’ visual signals. In this thesis, I make use of recent advances in measurement and analysis techniques, including digital video and image motion processing tools, to improve our understanding of how movement-based signals are adjusted according to signalling context. I measured and characterised the flamboyant claw-waving displays of male fiddler crabs (Genus Uca) and made use of their transparent lifestyle to record the behavioural contexts in which these signals are produced.¶ The claw-waving displays of seven Australian species of fiddler crab are compared and contrasted to show that these signals are species-specific, but also vary within and between individuals. I show that the species Uca perplexa produces different types of signal in different behavioural contexts, a lateral wave for courtship, and a vertical wave during short-range agonistic and courtship interactions. The structure of the lateral courtship waves of Uca perplexa vary according to the distance of signal receivers, the first time this kind of relationship has been shown in a dynamic visual signal. Finally, I describe and analyse the signalling and orientation behaviour of U. elegans during courtship herding, an unusual mating system that uses the claw-waving display in a novel way.¶ The adjustments made by fiddler crabs to their displays during changes in behavioural contexts suggest that the fine-scale context-sensitivity of animal signals may be far more widespread in communication than hitherto recognised.

No description available.

The Wilson’s Plover (Charadrius wilsonia) is a species of concern in most southeastern U.S. coastal states, where it breeds and winters. The U.S. Shorebird Conservation Plan listed this species as a Species of High Concern (Prioritization Category 4), and the U.S. Fish and Wildlife Service has designated it as a Bird of Conservation Concern (BCC). Despite its conservation status, Wilson’s Plover population trends are poorly understood and little research has been conducted examining habitat factors affecting this species’ breeding and foraging ecology. I collected Wilson’s Plover demographic data and explored which habitat characteristics influenced breeding success and foraging site selection among three coastal habitat types (i.e. fiddler crab (Uca spp.) mud flats, beach front, and interdune sand flats) at Onslow Beach, Marine Corps Base Camp Lejeune, North Carolina, 2008-2009. I observed little difference between years in nest success (≥ 1 egg hatched), failure, and overall nest survival. The majority of nest failures were caused by mammalian predators. For those nests that hatched successfully, greater proportions were located in clumped vegetation than on bare ground or sparsely vegetated areas. In-season chick survival for both years was higher for nests that hatched earlier in the season, and for nests farthest from the broods’ final foraging territory. Productivity estimates (chicks fledged per breeding pair) were not significantly different between years (0.88 ± 0.26 fledged/pair in 2008, 1.00 ± 0.25 fledged/pair in 2009) despite a shift in foraging behavior, possibly related to habitat alterations and availability in 2009. My findings indicate that Wilson’s Plover adults and broods were flexible in establishing final foraging territories; in 2008 all final brood foraging territories were on fiddler flats while in 2009, final foraging territories were sometimes split between fiddler flats, beach front, and interdune sand flats. For those Wilson’s Plovers establishing territories on fiddler flats, area of the flat was the most important feature explaining use versus non-use of a particular flat; area ≥ 1250 m² was preferred. Close proximity to water and vegetative cover were also important habitat features in foraging site selection on fiddler crab mud flats, and in all habitat types combined. My findings will directly contribute to population and habitat research goals outlined in the U.S. Shorebird Plan and will supplement limited data about foraging and habitat use related to Wilson’s Plover breeding ecology. / Master of Science

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / The present study investigated the effect of different strata of tide on the abundance, size, sex ratio, population structure, relative growth, morphological sexual maturity, amount of ovigerous females and reproductive burrows in U. leptodactylus. To this end, monthly collections were made from January to December 2013 in two strata of the intertidal, estuaries of Sergipe river and Vaza-barris river, using a square with internal area of 90cm², launched ten times randomly within each strata. For each stratum monthly measures air temperature, substrate temperature, water temperature, salinity and samples episubstrate for the determination of particle size and composition of organic matter were taken. In the laboratory, crabs were sexed, measured and preserved in 70% alcohol. The monthly results were statistically compared between strata and estuaries, there are similarities in environmental factors analyzed between strata, with an analysis of the abundance, size, relative growth and sexual maturity divergent between the same strata.The abundance and size of crabs were higher in the open strata of both estuaries, with the estuary of Vaza-barris river more abundant than estuary of Sergipe river, which in turn showed higher crabs. The sex ratio was not significantly different between the strata of the estuary of Vaza-barris river, but presented to the estuary of Sergipe river, where in the open strata occurred more males and more females in the vegetated strata. Population structure showed 19 classes of size 0.5 mm with modal distribution of recent juveniles for vegetated strata and adults to open strata. Juvenile and adult crabs showed positive allometric growth between carapace width and length of the propodus and width of the abdomen, separately for each sex. The fiddler crabs vegetated strata matured in smaller sizes than that observed for the open strata in both estuaries, in the estuary of Vaza-barris river males and females matured with 6.18 and 5.26 mm and 4.94 and 4.91 mm carapace width in open and vegetated strata, respectively. In the estuary of Sergipe river males and females matured with 5.61 and 5.36 and 5.24 mm and 4.39 mm carapace width in open and vegetated strata respectively. The similarity in abiotic factors between open and vegetated strata, and differences in the abundance, population structure and reproductive biology have led to the consideration of the reproductive behavior of lekking for U. leptodactylus. Ovigerous females and reproductive burrows occurred primarily in the open strata, so these areas were considered reproductive arenas, while vegetated strata were considered priority areas in recruitment. / O presente trabalho investigou o efeito de diferentes estratos de maré sobre a abundância, tamanho, razão sexual, estrutura populacional, crescimento relativo, maturidade sexual morfológica, quantidade de fêmeas ovígeras e tocas reprodutivas em U. leptodactylus. Para tal, foram realizadas coletas mensais no período de Janeiro à Dezembro de 2013 em dois estratos do entremarés, nos estuários do rio Sergipe e rio Vaza-barris, utilizando-se um quadrado com área interna de 90cm², lançado dez vezes aleatoriamente em cada estrato. Para cada estrato mensalmente foram tomadas as medidas de temperatura do ar, temperatura do substrato, temperatura da água, salinidade e amostras do episubstrato, para a determinação do teor de matéria orgânica e composição granulometria. Em laboratório, os caranguejos foram sexados, medidos e conservados em álcool 70%. Os resultados obtidos mensalmente foram comparados estatisticamente entre estratos e estuários, observou-se semelhança nos fatores ambientais analisado entre os estratos, sendo a análise da abundância, tamanho, crescimento relativo e maturidade sexual divergente entre os mesmos estratos. A abundância e o tamanho dos caranguejos foram maiores nos estratos abertos de ambos os estuários, sendo o estuário do rio Vaza-barris mais abundante do que o estuário do rio Sergipe, que por sua vez apresentou caranguejos maiores. A razão sexual não apresentou diferença significativa entre os estratos para o estuário do rio Vaza-barris, porém apresentou para o estuário do rio Sergipe, onde no estrato aberto ocorreram mais machos e nos estratos vegetados mais fêmeas. A estrutura populacional apresentou 19 classes de tamanho de 0,5 mm, com distribuição modal de juvenis recentes para os estratos vegetados e de adultos para os estratos abertos. Os caranguejos juvenis e adultos apresentaram crescimento alométrico positivo entre a largura da carapaça e comprimento do própodo e largura do abdômen, separadamente para cada sexo. Os chama-marés dos estratos vegetados maturaram em tamanhos menores do que o observado para os estratos abertos de ambos os estuários, no estuários do rio Vaza-barris os machos e fêmeas maturaram com 6,18 e 5,26 mm e 4,94 e 4,91 mm de largura da carapaça nos estratos aberto e vegetado, respectivamente. No estuário do rio Sergipe os machos e fêmeas maturaram com 5,61 e 5,36 mm e 5,24 e 4,39 mm de largura da carapaça nos estratos aberto e vegetado, respectivamente. A semelhança nos fatores abióticos entre os estratos abertos e vegetados, e as divergências na abundância, estrutura populacional e biologia reprodutiva, levaram à consideração do comportamento reprodutivo de lekking para U. leptodactylus. As fêmeas ovígeras e tocas reprodutivas ocorreram prioritariamente nos estratos abertos, portanto essas áreas foram consideradas arenas reprodutivas, enquanto os estratos vegetados foram considerados áreas prioritárias no recrutamento.