Specialist individuals within animal populations have shown to be more efficient foragers and/or to have higher reproductive success than generalist individuals, but interspecific reproductive consequences of the degree of diet specialisation in vertebrate predators have remained unstudied. Eurasian pygmy owls (hereafter POs) have less vole‐specialised diets than Tengmalm's owls (TOs), both of which mainly subsist on temporally fluctuating food resources (voles). To test whether the specialist TO is more limited by the main prey abundance than the generalist PO, we studied breeding densities and reproductive traits of co‐existing POs and TOs in central‐western Finland during 2002–2019. Breeding densities of POs increased with augmenting densities of voles in the previous autumn, whereas breeding densities of TOs increased with higher vole densities in both the previous autumn and the current spring. In years of vole scarcity, PO females started egg‐laying earlier than TOs, whereas in years of vole abundance TO females laid eggs substantially earlier than PO females. The yearly mean clutch size and number of fledglings produced of both POs and TOs increased with abundance of voles in the current spring. POs laid large clutches and produced large broods in years of both high and low vole abundance, whereas TOs were able to do so only in years of high vole abundance. POs were able to raise on average 73% of the eggs to fledglings whereas TOs only 44%. The generalist foraging strategy of POs including flexible switching from main prey to alternative prey (small birds) appeared to be more productive than the strictly vole‐specialized foraging strategy of TOs. In contrast to earlier studies at the individual‐level, specialist predators at the species level (in this case TOs) appear to be less effective than generalists (POs), but diet specialisation was particularly costly under conditions when scarcity of main foods limited offspring production.

中文翻译：

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通才和专家之间的区别：主要食物丰度的大幅波动对两种并存捕食者的数量和繁殖的影响

动物种群内的专家个体已显示出比通才个体更有效的觅食者和/或具有更高的繁殖成功率，但仍未研究脊椎动物捕食者中饮食专门化程度的种间繁殖后果。欧亚侏儒猫头鹰（以下简称POs）的田鼠专业饮食要比Tengmalm猫头鹰（TOs）少，后者都主要依靠时间上波动的食物资源（田鼠）生存。为了检验专家TO是否比通才PO受到主要猎物丰富度的限制，我们研究了芬兰中西部2002-2019年间PO和TO并存的繁殖密度和繁殖性状。在过去的秋季，PO的繁殖密度随田鼠的密度增加而增加，在过去的秋天和当前的春季，TOs的繁殖密度都随着田鼠密度的增加而增加。在田鼠稀少的年代，PO雌性开始产卵的时间要早​​于TOs，而在田鼠丰年的年代中，TO雌性的产卵时间要比PO雌性的早得多。随着春季春季田鼠数量的增加，PO和TO的年平均离合器尺寸和幼雏数量都增加了。PO在高田鼠丰度和低田鼠丰度的年份中都放下大离合器，并产生大量的育雏，而TOs仅在高田鼠丰度的年份中才能这样做。POs可以平均将73％的卵育成雏鸟，而TOs只能将其提高44％。PO的通才觅食策略（包括从主要猎物到替代猎物（小鸟）的灵活转换）比严格的专业TOS捕食策略更具生产力。与早期在个体水平上的研究相比，物种水平上的专业捕食者（在这种情况下为TOs）似乎不如通才（POs）有效，但是在主要食品短缺限制后代生产的情况下，饮食专业化特别昂贵。