Experimental evidence for state-dependent nest weight in the blue tit, Cyanistes caeruleus

Parental investment in reproduction is generally limited by food availability, and so avian life-history research has traditionally focused on the brood rearing phase, when food requirements are greatest. Only relatively recently has the focus extended to the incubation phase, and even more recently to the nest-building phase, where observational and comparative evidence suggest that avian nest building is an energetically expensive and time-consuming activity. We aimed to experimentally test the limitations on this cost in a hole-breeding passerine, the blue tit (Cyanistes caeruleus), by providing supplementary food to experimental pairs during the nest-building period. In comparison with control females, that did not receive supplementary food, experimental females constructed heavier nests, with greater amounts of moss base but similar amounts of cup lining, despite there being no differences in the time taken to build the nest. This study provides empirical support for the hypothesis that avian nest building is a costly behaviour, limited by food availability.     

Territorial responses of male blue tits, Cyanistes caeruleus , to UV-manipulated neighbours

Multiple phenotypic traits can affect the outcome of interactions among territorial animals. Individuals may use current and previously acquired information on phenotypic traits to assess the competitive ability of opponents and adjust the strength of their response depending on the threat the opponent poses. In birds, colourful plumage and song are widespread phenotypic traits. Recent work has shown that ultraviolet (UV) plumage reflectance may be used by males in assessing an opponent’s strength and by females in mate choice. In the present study, we investigated whether and how territorial male blue tits, Cyanistes caeruleus, use previously acquired information from UV reflectance of the crown feathers of neighbours to adjust their response to playback of song of these neighbours simulated to intrude their territory. We compared responses to neighbours with those to unfamiliar strangers with unknown plumage features. We found that subject males with UV-enhanced neighbours responded more strongly to these neighbours than to strangers, i.e. showed more flights, used songs without trill and tended to overlap more songs. Subject males with UV-reduced neighbours gave a lower or similar response to neighbours compared to strangers. This indicates that male blue tits combine previously acquired information about an intruder’s plumage with familiarity of its song, and that their response depends on the perceived quality of the neighbour. This study provides evidence that familiarity in combination with multiple signals of quality may influence territorial relations among neighbours.     

Experimental manipulation of testosterone and condition during molt affects activity and vocalizations of male blue tits

Testosterone (T) is a key hormone regulating behavioral trade-offs in male birds, shifting investment towards sexual and competitive behaviors. However, the role of T in regulating male behavior during the molt has received very little attention, although this is a crucial life-history stage. Since the effect of T on behavior may be condition-dependent, particularly during the costly molt period, we studied the effects of T and condition in a two-way design. We manipulated T under two dietary regimes (standard and improved, resulting in an enhanced condition) in captive blue tits (Cyanistes caeruleus) undergoing the first pre-basic molt. T treatment increased song frequency, indicating that song is T-dependent also at this time of year. Males on the improved diet sang less than males in relatively worse condition, providing no support for song as an indicator of male condition. T-treated males exhibited greater locomotor activity than control males, but only when fed the standard diet. Neither T- nor diet-treatment affected plumage maintenance (preening). Although T treatment resulted in a delay in molt progress all birds completed the molt. Taken together our results show that during the molt male birds are sensitive to relatively small fluctuations in T. Similar to its commonly observed effects during the breeding season, T stimulated an increase in song and locomotion. While there might be some benefits associated with such T effects, these must be traded-off against costs associated with conspicuous behavior and increased molt duration.     

Implications of conspecific background noise for features of blue tit, Cyanistes caeruleus , communication networks at dawn

Communication among animals often comprises several signallers and receivers within the signal’s transmission range. In such communication networks, individuals can extract information about differences in relative performance of conspecifics by eavesdropping on their signalling interactions. In songbirds, information can be encoded in the timing of signals, which either alternate or overlap, and both male and female receivers may utilise this information when engaging in territorial interactions or making reproductive decisions, respectively. We investigated how conspecific background noise at dawn may overlay and possibly constrain the perception of such singing patterns. We simulated a small communication network of blue tits, Cyanistes caeruleus, at dawn in spring. Two loudspeakers simulated a singing interaction which was recorded from four different receiver positions simulating potential eavesdroppers. During the recordings, resident blue tit males were vocalising and created natural conspecific background noise. Levels of conspecific background noise were high and varied among positions of potential eavesdroppers. We conclude that conspecific background vocalisations may potentially constrain the perception of singing patterns and may constitute costs for eavesdroppers. On the other hand, signallers may position themselves strategically and privatise their interactions.     

人工巢箱条件下杂色山雀的巢位选择及其对繁殖成功率的影响

杂色山雀(Parus varius)是一种分布区域极其狭窄的小型森林洞巢鸟类,种群数量稀少,在中国大陆仅见繁殖于辽宁省的东南部山区和毗邻辽宁的吉林省西南部山区,为当地留鸟.为了探讨巢址选择对杂色山雀繁殖的影响,找出影响杂色山雀繁殖成功率的巢址选择方面的主要因子,于2009-2011年3-7月,在辽宁省仙人洞国家级自然保护区通过悬挂人工巢箱,进行杂色山雀对人工巢箱的巢址选择以及不同的巢址对杂色山雀繁殖成功率的影响研究.研究表明:杂色山雀多在针阔混交林中活动和繁殖,对位于赤松与蒙古栎混交林中的巢箱有一定偏好.野外共发现24巢杂色山雀在人工巢箱中繁殖,其中15巢繁殖成功,9巢繁殖失败.对杂色山雀利用的巢址样方主成分分析表明,巢位因子( 19.826％)、乔木因子(17.571％)、灌木因子(13.11％)、光照因子(11.587％)、隐蔽因子(10.562％)和边缘效应因子(7.572％)是影响杂色山雀对人工巢箱选择的重要因子.利用巢箱与对照巢箱相比,两者在距水源距离、距路距离、乔木平均高度、灌木平均高度和植被类型这5个环境变量上存在显著差异.繁殖成功巢与繁殖失败巢相比,繁殖成功的巢箱所在位置距路稍远,坡度较高,乔木最大高度较高,灌木盖度略低于繁殖失败巢箱.人为干扰和天敌捕食是造成杂色山雀繁殖失败的主要原因.以上研究结果表明,巢向偏南、距地面2 m以上、周围乔木高大、灌木平均高度大于1.5m、盖度在45％-55％之间、距水源20 m左右、距路20 m以外的位于针阔混交林边缘的巢箱是杂色山雀繁殖的最优巢址.目前杂色山雀的种群数量还很稀少,希望本研究能对这一珍稀鸟类的保护提供重要参考.