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Deflected by the barrier function of topographical structures such as high mountain ranges, open water bodies or desert, migrating birds concentrate at certain points or corridors referred to as ‘bottlenecks’. An area like this was discovered at Mount Besh Barmag (Azerbaijan) in autumn 2007, but the data gathered during a four-week survey was insufficient to do more than hint at the existence of a major bird migration bottleneck. Therefore, a comprehensive bird migration study was conducted to analyse the magnitude of this potential bottleneck site. The study covers the periods from August to mid-November 2011 and from March to the end of May 2012 and includes daily counts at three observation points focusing on three different migrant types: passerine, waterbirds and soaring birds. In addition, a sound recorder with an omnidirectional microphone collected bird migration calls by both day and night. In total, 278 bird species were observed in an estimated passage of 1,239,369–1,514,267 diurnally migrating individuals in autumn 2011 and 646,733–817,183 individuals in spring 2012. Fifteen species passed through the study area in numbers exceeding 1% of their world populations and 34 species in more than 1% of their flyway populations in at least one of the observation periods. 84% of the observed migrating birds in autumn 2011 and 95% of them in spring 2012 passed through at heights below 50 m above ground exposing them imminently to the danger of collision with obstacles. In the analysis of nocturnal sound recordings, 119 bird species were identified of which 106 were expected to occur as migrants, and calculated estimates revealed the occurrence of 108,986 calls in autumn 2011 and 33,348 calls in spring 2012. The volume of diurnal bird migration emerging from the data with respect to species number and number of individuals is certainly a strong indication of the existence of a major bird migration bottleneck at Besh Barmag. On account of methodological constraints, the high number of night flight calls can only hint at a nocturnal bird migration bottleneck and confirmatory research aided by visual methods (radar, thermal imaging) is necessary to back up the acoustic results. The Besh Barmag bottleneck offers a great opportunity to establish a standardised long-term monitoring programme to investigate avian population dynamics in the vast and little known Eurasian landmass. Acoustic-based monitoring might be a cost-effective method, but it is limited to a few vocally prolific species only. The aim should rather be the establishment of a bird observatory as already successfully installed in a number of European bird migration bottlenecks.
Costs of reproduction. A demographical approach to examine life-history trade-offs ─ Abstract. Resource-allocation trade-offs are fundamental constraints of life-history evolution. In particular the trade-offs between reproduction and longevity and between present and future reproduction are expected to form reproductive patterns. Unfortunately, exploring such trade-offs in natural populations is complicated and may not be possible. In face of several limitations, zoo data appear to be useful to better understand the reproductive biology of endangered, rare or cryptic species. In the first step, it was sought after with a data-mining, comparative multi-species approach for broad patterns of correlations between lifespan and variables in bird-eating spiders (Theraphosidae). The subfamily Eumenophoriinae on average lived longest, followed by the Theraphosinae, Ornithoctinae, Grammostolinae, Selenocosmiinae, Ischnocolinae and finally the Avicularinae. Species inhabiting tropical, more humid and/or low-altitude environments lived longer, suggesting that more predictable environments favour the evolution of longer lifespans. Furthermore, large range size, low abundance, sub-terrestrial life-style, and aggressive behaviour were all linked with longer lifespans. An argument for resource allocation trade-offs was found as larger spiderling and prosoma size were negatively related to longevity. In the second step, a demographical approach has been applied for two old-world deer species (Vietnamese sika deer Cervus nippon pseudaxis, Mesopotamian fallow deer Dama dama mesopotamica). In both species, births peaked right before the onset of the rainy season in natural environments. Females reached high reproductive output earlier in life and had (in one species only) higher survival rates than males. Offspring number covaried positively rather than negatively with longevity. In females, the length of the reproductive phase correlated positively with longevity, birth rate within the entire lifespan, and offspring number, while it was negatively correlated to the birth rate during the reproductive phase (in one species). The length of the post-reproductive phase was positively related to longevity and negatively to birth rate during the entire lifespan. In the third section, life-histories of Asiatic (Equus hemionus ssp.) and African wild asses (Equus africanus ssp.) have been anlaysed in a comparative way with another demographical long-term approach. All taxa showed even in captivity peak birth rates during the periods of highest food availability in their natural environments. Sex-specific survival rates with females living longer than males were evident in Kulan and Onager but not in Kiang and Somali wild ass, pointing towards different life-history strategies even among closely related taxa. Females achieved their highest reproductive output earlier than males, which is typical for polygynous mating systems. Offspring number and longevity were rather positively correlated than negatively. Taken together evidence for reproductive trade-offs was weak, though the length of the reproductive period was negatively related to birth rates within the reproductive period. Birth intervals increased with female age, probably reflecting detrimental effects of senescence.
Presumably every organism on earth is involved in at least one mutualistic interaction with one or several other species. To interact with each other, the species need traits that provide benefits to the partner species. Surprisingly, the function of traits for the stabilization of mutualisms has rarely been investigated, despite of a general lack of knowledge how mutualisms are maintained. The aim of this work was to find functional traits, which stabilize the mutualism between a bat species and a carnivorous pitcher plant in Northern Borneo. Kerivoula hardwickii is the only bat species known to roost in pitcher-shaped trapping organs of Palaeotropical pitcher plants (Nepenthes). These bats fertilize the pitcher plant Nepenthes hemsleyana with their nutritious nitrogen-rich faeces while roosting inside the pitchers. The plants have outsourced capture and digestion of arthropod prey to the bats on which they strongly rely for nutrient acquisition. The bats in contrast are less dependent on their mutualism partner as they also roost in pitchers of two further Nepenthes species as well as in developing furled leaves of various plant species in the order Zingiberales. In earlier studies, we found that N. hemsleyana outcompetes alternative roosts by providing high-quality roosts for the bats. However, which traits exactly stabilize the mutualism between K. hardwickii and N. hemsleyana was still unclear. I found that both the bats and the pitcher plants show traits, which have the potential to stabilize their interaction. On the level of morphological traits, I found that the pitchers have a low fluid level and a particular shape that provide just enough roosting space for one individual of the solitary K. hardwickii, a mother with juvenile or a mating couple. The bats have enlarged thumb and foot pads that enable them to cling to the smooth surfaces of their roosts without using their claws. This avoids damage to the sensitive N. hemsleyana pitchers. On the level of communicational traits, again N. hemsleyana acquired morphological structures that act as effective ultrasound-reflectors, which guide the echo-orientating bats to the opening of the pitchers and help the bats to identify their mutualism partner. The bats’ calls on the other hand are characterized by extraordinary high starting frequencies and broad bandwidths, which enable K. hardwickii to easily locate pitchers of N. hemsleyana and other Nepenthes species in their dense habitats. Finally, on the level of behavioural traits the bats often but not always prefer their mutualism partner to other roosts when they can select roosts in their natural environment or in behavioural experiments. The reason for this behaviour seems to be a combination of 1) N. hemsleyana’s superior quality compared to alternative roosts and 2) different roosting traditions of the bats. In conclusion, the mutualism between bats and pitcher plants is asymmetric as N. hemsleyana is more dependent on K. hardwickii than vice versa. For the plants bat faeces present their most important nutrient source. In contrast, K. hardwickii can select between alternative roosting plants. This asymmetric dependency is reflected in the specifity and function of the traits that stabilize the mutualism in each of the two involved species. Especially on the morphological level, N. hemsleyana seems to have evolved several traits that perfectly fit to K. hardwickii. In contrast, the bats’ traits more generally facilitate their roosting in funnel-shaped plant structures and their occurrence in cluttered habitats. Thus, they are probably exaptations (i.e. traits that evolved for another reason) that are nevertheless functional and stabilize the mutualism with N. hemsleyana. This plant‘s superior roost quality is likely a consequence of the competition with alternative roosting plants and is a pre-requisite for the bats to prefer N. hemsleyana. Moreover, my study confirms earlier findings that asymmetric dependencies support the stabilization of mutualistic interactions. Finally, my work indicates that the specifity of functional traits can be used as a measure to determine mutual dependencies of mutualistic partners.