The Large Communal Nests of Sociable Weavers Provide Year-Round Insulated Refuge for Weavers and Pygmy Falcons

The primary role of nests as structural support for eggs, nestlings, and incubating parents is well established, but our understanding of their secondary roles and their adaptive features is still limited. Nests can serve a particularly important role in protecting or buffering birds from weather. In hot, arid environments, maximum daily temperatures can exceed a species' upper critical temperature threshold and during the non-breeding season temperatures may also drop below freezing. Nest structures that help buffer against extreme temperatures may play a crucial role in managing the costs of thermoregulation, especially those nests that are used and maintained year-round. We use extensive year-round data to investigate the thermal benefits of massive colonial structures built by sociable weavers in the arid savannahs of the Kalahari, South Africa. These colonies consist of multiple nesting chambers and are used as roosts when birds are not breeding. We explored whether these structures provide thermal buffering throughout the year and how individual chamber placement within the colony and features of the chambers influenced their thermal buffering capacity. We also investigated whether nest chambers occupied and modified by an obligate nest parasite, the African pygmy falcon provided additional thermal buffering. Our results show that sociable weaver colonies provide thermal benefits throughout the year, buffering both hot and cold ambient extremes. Chambers with longer entrance tunnels provided better insulation than chambers with shorter entrance tunnels, and chambers located toward the center of a colony provided greater insulation than chambers at the edge. Chambers occupied by falcons did not display additional thermal benefits, which may be due to falcons choosing chambers with shorter entrance tunnels. Because falcons are larger than weavers, they may find it harder to enter chambers with longer entrance tunnels, and/or because weavers cease maintenance of those chambers. In conclusion, the communal nests of sociable weaver provide thermal benefits to weavers and heterospecifics alike, creating a more optimal environment for breeding, roosting and reducing thermal stress. In a landscape that is becoming increasingly harsh under climate change, the importance of these structures to the local animal communities may also increase

Chicks of the Great Spotted Cuckoo May Turn Brood Parasitism into Mutualism by Producing a Foul-Smelling Secretion that Repels Predators

The great spotted cuckoo (Clamator glandarius) is an important brood parasite of carrion crows (Corvus corone corone) in northern Spain. We recently found that, unlike what is commonly known for cuckoo-host interactions, the great spotted cuckoo has no negative impact on average crow fitness in this region. The explanation for this surprising effect is a repulsive secretion that the cuckoo chicks produce when they are harassed and that may protect the brood against predation. Here, we provide details on the chemical composition of the cuckoo secretion, as well as conclusive evidence that the dominating volatile chemicals in the secretion are highly repellent to model species representative of common predators of the crows. These results support the notion that, in this particular system, the production of a repulsive secretion by the cuckoo chicks has turned a normally parasitic interaction into a mutualistic one

Parasitism and cooperation in the nests of carrion crows

El objetivo principal de esta tesis es profundizar en el estudio de las interacciones de la corneja negra Corvus corone corone con el críalo Clamator glandarius, un ave parásita de cría que pone los huevos en nidos de otras especies, los hospedadores, para que los incuben y críen los pollos junto a los suyos propios. En el Paleártico, su hospedador primario es la urraca Pica pica, mientras que la corneja es el secundario; sin embargo, en la población de estudio, situada en el norte de España, el críalo usa la corneja como hospedador primario, en vez de la urraca. Esta situación da la oportunidad de investigar en más detalle las interacciones parásito-hospedador entre la corneja y el críalo. Este sistema es especialmente interesante debido a una diferencia notable frente a la mayoría de los estudios realizados: la especie hospedadora es más grande que la parásita. Esta característica puede dar lugar a que el resultado de la interacción parásito-hospedador presente diferencias significativas frente a sistemas en los que el tamaño de las especies es igual o la especie parásita es más grande.Departamento de Ciencias Agroforestale

Corneja negra – Corvus corone Linnaeus, 1758

Aves - Orden Passeriformes - Familia Corvidae en la Enciclopedia Virtual de Vertebrados Españoles, http://www.vertebradosibericos.org/. Versiones anteriores: 10-11-2009A comprehensive review of the natural history of the Carrion crow Corvus corone in Spain.Peer reviewe

The large communal nests of sociable weavers provide year-round insulated refuge for weavers and pygmy falcons

The primary role of nests as structural support for eggs, nestlings, and incubating parents is well established, but our understanding of their secondary roles and their adaptive features is still limited. Nests can serve a particularly important role in protecting or buffering birds from weather. In hot, arid environments, maximum daily temperatures can exceed a species’ upper critical temperature threshold and during the nonbreeding season temperatures may also drop below freezing. Nest structures that help buffer against extreme temperatures may play a crucial role in managing the costs of thermoregulation, especially those nests that are used and maintained year-round. We use extensive year-round data to investigate the thermal benefits of massive colonial structures built by sociable weavers in the arid savannahs of the Kalahari, South Africa. These colonies consist of multiple nesting chambers and are used as roosts when birds are not breeding. We explored whether these structures provide thermal buffering throughout the year and how individual chamber placement within the colony and features of the chambers influenced their thermal buffering capacity. We also investigated whether nest chambers occupied and modified by an obligate nest parasite, the African pygmy falcon provided additional thermal buffering. Our results show that sociable weaver colonies provide thermal benefits throughout the year, buffering both hot and cold ambient extremes. Chambers with longer entrance tunnels provided better insulation than chambers with shorter entrance tunnels, and chambers located toward the center of a colony provided greater insulation than chambers at the edge. Chambers occupied by falcons did not display additional thermal benefits, which may be due to falcons choosing chambers with shorter entrance tunnels. Because falcons are larger than weavers, they may find it harder to enter chambers with longer entrance tunnels, and/or because weavers cease maintenance of those chambers. In conclusion, the communal nests of sociable weaver provide thermal benefits to weavers and heterospecifics alike, creating a more optimal environment for breeding, roosting and reducing thermal stress. In a landscape that is becoming increasingly harsh under climate change, the importance of these structures to the local animal communities may also increase.(Paper provisionally accepted to Frontiers in Ecology and Evolution. DOI to follow.)</div

Number cuckoo eggs

Number of cuckoo eggs in magpie and crow nests in the two studied populations. See previous file for further description

Santa Clara

An archive of the Santa Clara University student newspaper from Santa Clara University in Californi

Data from: Spatiotemporal variation of host use in a brood parasite: the role of the environment

Avian brood parasites should target the most profitable host species, but current conditions might locally influence their choice, producing geographic mosaics of coevolution. Throughout Europe, the magpie Pica pica has been invariably reported as the primary host of the great spotted cuckoo Clamator glandarius, whereas the carrion crow Corvus corone is the secondary one. However, we found that this pattern reversed in northern Spain, where up to 70% of carrion crow nests were parasitized versus 20% of magpie nests. In southern Spain, conversely, parasitism increased proportionally in both hosts (up to approximately 90% of available nests) throughout the 3 years of study. Surprisingly, magpies provided the best reproductive output for cuckoos in both areas, in contrast with cuckoo’s preference for the crow host in the north. Genetic data ruled out the presence of different host-specific races in this brood parasite, dismissing the hypothesis that a prevalence of different gentes at the 2 sites explained the observed variability in host choice. Instead, we found that magpie nests in the south were easier to reach and more scattered than in the north, where cuckoos preferentially targeted nests that were less concealed and more isolated. We suggest that the habitat constraints parasitism on magpies in the north, driving cuckoo host choice toward the crows. The coevolutionary scenario therefore includes a 3-way interaction, where the pressure that the parasite puts on a host species in a given place critically depends on the environmentally mediated interaction between the same parasite and a different host