IMPLICATIONS AND FUTURE DIRECTIONS

(a) The fitness consequences of light pollution

Although there is increasing interest in the ecological effects of light pollution, yet there is a surprising lack of knowledge about the fitness consequences of artificial light at night. Most of the studies on this topic have reported about light pollution as a source of immediate mortality, for example for migrating birds, hatchling sea-turtles, insects (Rich

& Longcore 2006). However, very little is known about other aspects of fitness-related traits or events, such as reproduction and senescence. In birds, recent evidence has shown that light at night can affect extra-pair paternity gain and provisioning rate to the chicks (Kempenaers et al. 2010; Titulaer et al. 2012). While it is clear that extra-pair paternity can increase male reproductive output, higher feeding rate likely imposes greater energetic demands on the adults. Whether they are able to compensate for such higher energy expenditure it is unknown, but even if they would, a cost for the resulted higher metabolism could be paid as increased oxidative stress, higher rate of telomeres loss, and ultimately faster senescence (Monaghan et al. 2008). From a chick perspective, although there might be advantages in growing faster, costs can be faced later in life (Metcalfe &

Monaghan 2001).

A potentially fitness-related aspect to be considered is the variation in circadian rhythms observed in urban blackbirds. Circadian rhythms are ubiquitous among animal and plant species, and they are though to reflect adaptation to the 24 h light/dark cycle. Although we suggested that a shorter circadian period length could be adaptive in urban areas (Chapter 4), we do not have data to test this hypothesis. Furthermore, de-synchronization between the circadian clock and the external environment as a consequence of the exposure to light at night can cause profound physiological effects that can increase tumor development, alter metabolism, induce oxidative stress (Navara & Nelson 2007).

However, so far these mechanisms have been studied mainly in humans, but very little is known about the effects of light at night of circadian rhythms in wild species. Our study is the first to investigate a potential relationship between environmental change (urbanization) and circadian rhythms in birds, and we suggest that future research should look at i) whether the shift in circadian traits in urban birds is a consequence of micro-evolution or phenotypic flexibility and ii) what are the fitness consequences of such shift.

Finally, it is crucial to understand what the consequences of an altered timing of reproduction are for urban birds. Early breeding has been recorded in several urbanized avian species (Schoech & Bowman 2003; Partecke et al. 2005; Chamberlain et al. 2009).

Although it has been suggested that early breeders of multiple nesting species can potentially increase the number of clutches per breeding season and therefore, potentially, the yearly reproductive output (Partecke et al. 2005; Chamberlain et al. 2009), very little is known of the survival of these broods. In addition, to breed early in the season when temperatures are still low and food availability scarce might impose additional energetic

costs and affect life-history trade-offs, such as that between immune-function and reproduction (Martin, Hasselquist, & Wikelski 2006; Martin, Weil, & Nelson 2007).

(b) Effects of light pollution at the ecosystem scale

The results of this thesis highlight that avian species that colonized urban areas might extend their activity into the night. Temporal niche switching is not a rare phenomenon in nature (Mrosovsky & Hattar 2005), and it has been extensively studied in mammals and invertebrate aquatic species (Mrosovsky & Hattar 2005; Chiesa et al. 2010; Hut et al.

2012). Since many relationship between species, such as predator-prey interactions, largely depend on the time when species are active, it is clear that temporal niches are an important factor for ecological networks and ecosystem functioning (Pahl-Wostl 1990;

Chesson, Pacala, & Neuhaser 2001). Indeed, the maintenance of temporal niches is one of the emerging aspects of modern conservation biology (Wiens et al. 2010). External factors such as interspecifc competition for resources and predation are classic examples of environmental pressures that are able to drive temporal nice switching (Valeix, Chamaillé-Jammes, & Fritz 2007; McCauley et al. 2012). In recent years, artificial light at night has been suggested as one anthropogenic source of variation in the temporal environment that could promote changes in the time, type and degree of interactions between competing species (Longcore & Rich 2004; Navara & Nelson 2007; Rotics, Dayan, & Kronfeld-Schor 2011). In the specific context of this thesis, changes in the daily and seasonal timing of activities of European blackbirds could potentially result in a modification of the relationship with both prey and predator species. For example,

that not only the amount, but also the composition of the invertebrate community may be modified by artificial lights (Davies, Bennie, & Gaston 2012). The higher availability of insects has been suggested as a potential indirect effect of light pollution on the timing of dawn song in some bird species (Kempenaers et al. 2010), but experimental evidence is lacking. Furthermore, songbirds themselves are food for other species, such as hawks, owls and mammalian predators like weasels and cats, but nothing is known on the responses of these predators to the change in the timing of daily activity patterns of their preys. In addition, what are the consequences of an early breeding of urban birds at other levels of the food web? For example, is early timing of reproduction of urban blackbirds related to an early phenology of plant and insect species? And are nest predators of blackbirds responding to the earlier availability of their major food source? These questions have been investigated in good detail in other ecological systems, for example the effect of climate change on the phenology of oak, caterpillars and songbirds (Both et al. 2009), but very little has been to expand such a framework in the context of urban ecology (Shochat et al. 2006, 2010). I believe that, given the strong impact of light pollution on daily and seasonal cycles of different animal species, it is high time for scientists to start integrating knowledge and methods from different fields to elucidate the effects of artificial light at night on ecosystem functioning.

Acknowledgements

I wouldn’t be here without the constant support that my family provided me throughout all my life. My first acknowledgement is for my mother, who grew me up, taught me taught me how to be a scientist, and I am very much thankful to him because he mentored me with the consciousness and experience of an old Professor, even though he is one of the youngest group leaders that I met. He always guided me towards the right path, but at the same time he gave me full freedom to develop my ideas. Thank you, Jesko.

This work has benefited from the supervision of a terrific PhD committee. Till Roenneberg, Martin Wikelski, Ela Hau and Barbara Helm have provided me with comments, ideas, positive critiques and suggestions. I am particularly thankful to Barbara, who has welcome me in her house in Scotland for more than two months, has guided me in developing new ideas for two chapters of this thesis, and has become what I would call a friend. Till Roenneberg lost his driving license and had to pay hundreds of euro of fine because he kindly agreed to join my PAC meeting in Radolfzell. I thank Ela who kindly supported me as official Professor at Uni Konstanz, and because I learned a lot from her positive approach to life and work.

I am grateful to have spent an important part of my life at the MPIO in Radolfzell. I met

been very close to me in a particular moment of my life. I am very happy to have shared my office during the last months with Scott LaPoint. We not only shared an office space, but it was great to discuss ideas, projects, dreams, and basketball! I thank all my wonderful colleagues and friends Sjouke, Bart, Riek, Jenny, Aki, Daniel, Yann, Dina, Tim, Anne, Marielle, Jessica and many others. Karl-Heinz was my first encounter coming here, and I will never forget that! Many amazing animal caretakers have helped me maintaining my blackbirds population in the lab, and without them a big part of this thesis would have not been written on pages today. I thank Elke and all the administration people, your help has been much appreciated by me. Daniel Piechowski has been great with all IMPRS-related stuff. Finally, I thank Bruno Erne, Hubert Fink and Georg Heine for producing light loggers for us. A good part of this thesis has been done because of your great job!

A great hug is for Rebecca and Oliver, my first German friends. Our roads crossed by chance one evening in Raisting, and I am so happy that they did.

I live for two years with amazing people on the island of Reichenau. They taught me German language, how to make Käsespätzle, how to take care of a garden. Some of them became great friends, like Max, Mely and Ale. I am glad I met you! A special thought is for Brynia, who is not among us anymore, but still lives in our happiest memories. I hope you flew to a better place.

Although somehow far, I still have great friends in Italy. I thank them with heart, and with no particular reason, but just because they are my friends. I especially thank Cecilia, Enrico, Sam, Francesca, Melissa, because they have been very close to me in summer 2012, one of the darkest periods of my life. I would not have made it without your support, energy and friendship!

I thank all the people in Seewiesen with whom I shared my time off during three field seasons in Bavaria. Sarah, Bea, Brecht, Pietro, Hendrik, Stefan, Yimen, Sol, Eileen, Tessa, Addy, Pernilla, Andres, Lisa, Anne. I also thank Bashi, Nicole Hoiss and Kerstin

for providing me accommodation and office space. Hannes Sagunsky provided me great technical support.

I thank Elena for her great motivation during the last weeks. Your power and energy has helped me a lot going through the hard times. Obrigado!

One of the best things which happened to me during the last four years is to have raised a dog. Malu’, du bist der hammer! You have given me so much power, energy, responsibility, happiness, little sleep, laughs. I will always bring you with me, everywhere, promise!

Finally, I want to thank Kim. No matter what happened in the end, you are my first memory of the time I spent here in Germany. You are probably also the main reason why this experience has been a wonderful adventure in itself. Thank you.