Juan Diego Ibáñez-Álamo

The geography of fear: a latitudinal gradient in anti-predator escape distances of birds across Europe

All animals flee from potential predators, and the distance at which this happens is optimized so the benefits from staying are balanced against the costs of flight. Because predator diversity and abundance decreases with increasing latitude, and differs between rural and urban areas, we should expect escape distance when a predator approached the individual to decrease with latitude and depend on urbanization. We measured the distance at which individual birds fled (flight initiation distance, FID, which represents a reliable and previously validated surrogate measure of response to predation risk) following a standardized protocol in nine pairs of rural and urban sites along a ca. 3000 km gradient from Southern Spain to Northern Finland during the breeding seasons 2009–2010. Raptor abundance was estimated by means of standard point counts at the same sites where FID information was recorded. Data on body mass and phylogenetic relationships among bird species sampled were extracted from the literature. An analysis of 12,495 flight distances of 714 populations of 159 species showed that mean FID decreased with increasing latitude after accounting for body size and phylogenetic effects. This decrease was paralleled by a similar cline in an index of the abundance of raptors. Urban populations had consistently shorter FIDs, supporting previous findings. The difference between rural and urban habitats decreased with increasing latitude, also paralleling raptor abundance trends. Overall, the latitudinal gradient in bird fear was explained by raptor abundance gradients, with additional small effects of latitude and intermediate effects of habitat. This study provides the first empirical documentation of a latitudinal trend in anti-predator behavior, which correlated positively with a similar trend in the abundance of predators.

Escape behaviour of birds provides evidence of predation being involved in urbanization

Altered predation risk in urban environments may contribute to animals becoming successfully urbanized by individuals from rural habitats. Escape behaviour has evolved to allow an individual to escape once captured by a predator. We tested whether altered predation risk in urban environments is associated with colonization of such habitats by comparing escape behaviour of 1132 individual birds belonging to 15 species from nearby rural and urban populations when captured by a human. Raptors (of which the Eurasian sparrowhawk, Accipiter nisus, was one of the most common species) were more common in rural than in urban habitats, whereas cats, Felis catus, showed the opposite pattern. There were consistent differences in escape behaviour between habitats, showing divergence in behaviour from the ancestral rural state. Urban birds wriggled less, showed higher tonic immobility, more often lost feathers, were less aggressive by biting less often, and emitted fear screams and alarm calls more often than rural birds. Furthermore, differences in escape behaviour between habitats were related to susceptibility to predation by sparrowhawks, as expected if differences in behaviour were due to differences in predation risk. Finally, an analysis of differences in escape behaviour between rural and urban birds revealed a significant relationship with time since urbanization, suggesting that escape behaviour has changed in urban environments over time. These findings suggest that release from predation and change in predator community associated with urbanization has altered the antipredator behaviour of birds colonizing towns and cities.

Nest predation research: Recent findings and future perspectives

Nest predation is a key source of selection for birds that has attracted increasing attention from ornithologists. The inclusion of new concepts applicable to nest predation that stem from social information, eavesdropping or physiology has expanded our knowledge considerably. Recent methodological advancements now allow focus on all three players within nest predation interactions: adults, offspring and predators. Indeed, the study of nest predation now forms a vital part of avian research in several fields, including animal behaviour, population ecology, evolution and conservation biology. However, within nest predation research there are important aspects that require further development, such as the comparison between ecological and evolutionary antipredator responses, and the role of anthropogenic change. We hope this review of recent findings and the presentation of new research avenues will encourage researchers to study this important and interesting selective pressure, and ultimately will help us to better understand the biology of birds.

Experimental evidence for a predation cost of begging using active nests and real chicks

AbstractThe existence of begging costs has recently been the focus of evolutionary studies on parent–offspring conflict. Indirect findings seem to support the existence of a nest predation cost of begging. However, empirical direct evidence of nestling begging attracting the attention of nest predators has been criticized because of methodological problems, mainly the use of artificial nests and playbacks. In order to avoid this problem, we used natural and active nests and real chicks. We utilized Common Blackbird (Turdus merula) nests to experimentally create high and control begging nests by introducing a Great Spotted Cuckoo (Clamator glandarius) or Blackbird chick respectively. We also explored the effect of brood size comparing between Blackbird broods augmented and reduced by one chick. Experimentally parasitized nests were significantly more predated than simply augmented or reduced broods: nest predation for Cuckoo introduced (high begging) nests was more than double that predation for nests of the other two groups. However, we did not find any effect of the brood size. The presence of a Great Spotted Cuckoo chick in a nest also favors an earlier detection of the nest by predators. Parental activity at the nests seems not to be a factor explaining these results as we did not detect significant differences between Cuckoo and Blackbird introduced nests in visit rates. Therefore, our findings support the hypothesis that nestling begging has a severe cost in terms of predation and, hence, this cost may impose an important restriction to the evolution of begging behavior.ZusammenfassungPrädationskosten von Bettelrufen: ein experimenteller Nachweis anhand von aktiven Nestern und echten Küken In den letzten Jahren gab es mehrere evolutionäre Untersuchungen zu den Kosten von Bettelrufen vor dem Hintergrund von Konflikten zwischen Eltern und Nachwuchs. Indirekte Nachweise scheinen diese Kosten in Form von erhöhter Nestprädation zu bestätigen. Direkte Nachweise dafür, dass Bettelrufe Nestprädatoren anziehen können, riefen jedoch methodische Kritik hervor, da sie hauptsächlich künstliche Nester und Playback verwandten. Um diese Probleme zu vermeiden, haben wir in der vorliegenden Untersuchung natürliche, aktive Nester und echte Küken verwandt. Wir gebrauchten Amselnester (Turdus merula) und schufen experimentell Nester mit verstärkten Bettelrufen, indem wir ein Kuckucksküken (Clamator glandarius) hinzufügten, sowie Kontrollnester, zu welchen ein extra Amselküken zugefügt wurde. Zudem haben wir den Effekt von Gelegegröße untersucht, indem wir Amselgelege jeweils um ein Küken verkleinert oder vergrößert haben. Experimentell parasitierte Nester wurden signifikant häufiger prädiert als anderweitig veränderte Nester, wobei die Nestprädation mehr also doppelt so hoch war wie bei Nestern der anderen zwei Gruppen. Wir fanden keinen Effekt von Gelegegröße. Die Anwesenheit eines Kuckuckskükens hat sich auch auf den früheren Zeitpunkt der Entdeckung des Nestes durch einen Prädator ausgewirkt. Die Aktivität der Eltern am Nest schien kein wichtiger Faktor zu sein: wir fanden keine Unterschiede in den Besuchsraten zwischen den Nestern mit Kuckucksküken und den Nestern ohne. Unsere Ergebnisse unterstützen die Annahme, dass Bettelrufe starke Prädationskosten hervorrufen können; diese Kosten können deshalb potentiell die Evolution von Bettelrufen stark beeinflussen.

Urbanized birds have superior establishment success in novel environments

Many animals have adapted to the proximity of humans and thereby gained an advantage in a world increasingly affected by human activity. Numerous organisms have invaded novel areas and thereby increased their range. Here, we hypothesize that an ability to thrive in urban habitats is a key innovation that facilitates successful establishment and invasion. We test this hypothesis by relating the probability of establishment by birds on oceanic islands to the difference in breeding population density between urban and nearby rural habitats as a measure of urbanization in the ancestral range. This measure was the single-most important predictor of establishment success and the only statistically significant one, with additional effects of sexual dichromatism, number of releases and release effort, showing that the ability to cope with human proximity is a central component of successful establishment. Because most invasions occur as a consequence of human-assisted establishment, the ability to cope with human proximity will often be of central importance for successful establishment.

Predator-induced female behavior in the absence of male incubation feeding: an experimental study

Parental care plasticity is critical to understanding the ecological and evolutionary influence of nest predation on life history strategies. In birds, incubation imposes a trade-off between the requirements of females (i.e., food) and egg requirements (i.e., heat and protection from predators). However, studies on this topic are rare and usually restricted to species where the male feeds the incubating female, relaxing her incubation costs. Males and females can reduce their activity at the nest to avoid detection by predators. However, females could follow two alternative antipredator strategies: to delay their return to the nest to avoid attracting attention from the potential predator or to return to the nest as soon as possible to enhance nest concealment. In this study, we manipulated the perceived risk of nest predation of incubating common blackbirds (Turdus merula), a species without incubation feeding, to study female behavioral changes induced by nest predation risk. We show experimentally that female blackbirds can reduce their nest visits in the situation with higher nest predation risk. In addition, we confirm that females significantly delay their return to the nest in the presence of a nest predator, contradicting the nest concealment hypothesis. However, our results could be interpreted as a passive antipredator response (to minimize clues given to predators) or as an active antipredator response (to search for predators to expel them from their territories).

A long-term experimental study demonstrates the costs of begging that were not found over the short term.

Parent–offspring conflict theory predicts that begging behaviour could escalate continuously over evolutionary time if it is not prevented by costliness of begging displays. Three main potential physiological costs have been proposed: growth, immunological and metabolic costs. However, empirical evidence on this subject remains elusive because published results are often contradictory. In this study, we test for the existence of these three potential physiological costs of begging in house sparrow (Passer domesticus) nestlings by stimulating a group of nestlings to beg for longer and another group for shorter periods than in natural conditions. All nestlings were fed with the same quantity of food. Our study involves a long-term experimental treatment for begging studies (five consecutive days). Long-term studies frequently provide clearer results than short-term studies and, sometimes, relevant information not reported by the latter ones. Our long-term experiment shows (i) a clear effect on the immune response even since the first measurement (6 hours), but it was higher during the second (long-term) than during the first (short-term) test; (ii) evidence of a growth cost of begging in house sparrow nestlings not previously found by other studies; (iii) body condition was affected by our experimental manipulation only after 48 hour; (iv) a metabolic cost of begging never previously shown in any species, and (v) for the first time, it has shown a simultaneous effect of the three potential physiological costs of begging: immunocompetence, growth, and metabolism. This implies first, that a multilevel trade-off can occur between begging and all physiological costs and, second, that a lack of support in a short-term experiment for the existence of a tested cost of begging does not mean absence of that cost, because it can be found in a long-term experiment.

Global loss of avian evolutionary uniqueness in urban areas

Abstract Urbanization, one of the most important anthropogenic impacts on Earth, is rapidly expanding worldwide. This expansion of urban land‐covered areas is known to significantly reduce different components of biodiversity. However, the global evidence for this effect is mainly focused on a single diversity measure (species richness) with a few local or regional studies also supporting reductions in functional diversity. We have used birds, an important ecological group that has been used as surrogate for other animals, to investigate the hypothesis that urbanization reduces the global taxonomical and/or evolutionary diversity. We have also explored whether there is evidence supporting that urban bird communities are evolutionarily homogenized worldwide in comparison with nonurban ones by means of using evolutionary distinctiveness (how unique are the species) of bird communities. To our knowledge, this is the first attempt to quantify the effect of urbanization in more than one single diversity measure as well as the first time to look for associations between urbanization and phylogenetic diversity at a large spatial scale. Our findings show a strong and globally consistent reduction in taxonomic diversity in urban areas, which is also synchronized with the evolutionary homogenization of urban bird communities. Despite our general patterns, we found some regional differences in the intensity of the effect of cities on bird species richness or evolutionary distinctiveness, suggesting that conservation efforts should be adapted locally. Our findings might be useful for conservationists and policymakers to minimize the impact of urban development on Earths biodiversity and help design more realistic conservation strategies. &NA; We investigated the hypothesis that urbanization reduces the global taxonomic and/or evolutionary diversity in birds. We found a strong and globally consistent reduction in taxonomic diversity in urban areas, which is also synchronized with the evolutionary homogenization of urban bird communities. Despite our general patterns, we found some regional differences in the intensity of the effect of cities on bird species richness or evolutionary distinctiveness, suggesting that conservation efforts should be adapted locally. Figure. No caption available.

Great spotted cuckoo fledglings are disadvantaged by magpie host parents when reared together with magpie nestlings

The post-fledging period is a critical phase for juvenile survival, and parental care provided during this period is a key component of avian reproductive performance. Very little is known about the relationships between foster parents and fledglings of brood parasites. Here, we present the results of a 5-year study about the relationships between fledglings of the non-evictor brood parasitic great spotted cuckoo (Clamator glandarius) and its magpie (Pica pica) foster parents. Sometimes, great spotted cuckoo and magpie nestlings from the same nest can fledge successfully, but most often parasitic nestlings outcompete host nestlings and only cuckoos leave the nest. We have studied several aspects of cuckoo post-fledging performance (i.e. feeding behaviour, parental defence and fledgling survival) in experimental nests in which only cuckoos or both magpie and cuckoo nestlings survived until leaving the nest. The results indicate that great spotted cuckoo fledglings reared in mixed broods together with magpie nestlings were disadvantaged by magpie adults with respect to feeding patterns. Fledgling cuckoos reared in mixed broods were fed less frequently than those reared in only cuckoo broods, and magpie adults approached less frequently to feed cuckoos from mixed broods than cuckoos from only cuckoo broods. These results imply that the presence of hosts own nestlings for comparison may be a crucial clue favouring the evolution of fledgling discrimination; and furthermore, that the risk of discrimination at the fledgling stage probably is an important selection pressure driving the evolution of the arms race between brood parasites and their hosts.

Does Nest Predation Risk Induce Parent Birds to Eat Nestlings' Fecal Sacs? An Experimental Study

Adult birds are frequently observed consuming nestling feces. However, fecal sac ingestion has received little attention, including a lack of experimental tests to understand such behavior. Traditionally, it has been explained by the “parental nutrition hypothesis” (parents acquire nutrients and energy) or the “economic disposal hypothesis” (parents save time to do other tasks). Here, we propose a third explanation, the “nest predation hypothesis”: parents ingest fecal sacs to reduce nest detectability in the presence of a nest predator. We experimentally manipulated the nest-predation risk perceived by adult common blackbirds (Turdus merula). We detected an effect of brood size in the removed and ingested feces while our experiment did not increase fecal sac comsumption. However, we found other evidences supporting that nest predation could play a more subtle role in this parental care behavior: (1) both sexes contributed equally to fecal ingestion; (2) adults ingested more feces in the population with the highest nest-predation risk; and (3) parents that ate fecal sacs increased their permanence at the nest.