Frederiksen Morten, Bregnballe Thomas
National Environmental Research Institute, Department of Coastal Zone Ecology, Kalø, Grenåvej 12, DK-8410 Rønde, Denmark.
J Anim Ecol. 2000 Sep;69(5):737-752. doi: 10.1046/j.1365-2656.2000.00435.x.
1. The increasing population of cormorants (Phalacrocorax carbo sinensis) in Europe since 1970 has led to conflicts with fishery interests. Control of cormorant populations is a management issue in many countries and a predictive population model is needed. However, reliable estimates of survival are lacking as input for such a model 2. Capture-recapture estimates of survival of dispersive species like cormorants suffer from an unknown bias due to permanent emigration from the study area. However, a combined analysis of resightings and recovery of dead birds allows unbiased estimates of survival and emigration. 3. We use data on 11 000 cormorants colour-ringed as chicks in the Danish colony Vorsø 1977-97 to estimate adult survival and colony fidelity. Recent statistical models allowing simultaneous use of recovery and resighting data are employed. We compensate for variation in colour-ring quality, and study the effect of population size and winter severity on survival, as well as of breeding success on fidelity by including these factors as covariates in statistical models. 4. Annual adult survival fluctuated from year to year (0·74-0·95), with a mean of 0·88. A combination of population size in Europe and winter temperatures explained 52-64% of the year-to-year variation in survival. Differences in survival between sexes was less than 1%. Cormorants older than ≈ 12 years experienced lower survival, whereas second-year birds had survival similar to adults. Colony fidelity declined after 1990 from nearly 1 to ≈ 0·90, implying 10% permanent emigration per year. This change coincided with a decline in food availability. 5. Apparently, survival was more severely affected by winter severity when population size was high. This could be caused by saturation of high-quality wintering habitat, forcing some birds to winter in less good habitat where they would be more vulnerable to cold winters. There was thus evidence for density dependence in adult survival, at least in cold winters. 6. The high population growth rate sustained by European Ph. c. sinensis in the 1970s and 1980s can partly be accounted for by unusually high survival of immature and adult birds, probably caused by absence of hunting, low population density and high food availability.
自1970年以来，欧洲鸬鹚（Phalacrocorax carbo sinensis）数量不断增加，这引发了与渔业利益的冲突。在许多国家，控制鸬鹚数量是一个管理问题，因此需要一个预测种群模型。然而，缺乏可靠的存活率估计值作为该模型的输入数据。
对于像鸬鹚这样具有扩散性的物种，由于其会永久性地迁出研究区域，捕获 - 重捕法对其存活率的估计存在未知偏差。然而，对鸟类重新观察和死亡鸟类回收情况进行综合分析，可以得到无偏差的存活率和迁出率估计值。
我们使用1977 - 1997年在丹麦Vorsø殖民地作为雏鸟佩戴彩色环志的11000只鸬鹚的数据，来估计成年鸬鹚的存活率和对繁殖地的忠诚度。我们采用了最近允许同时使用回收和重新观察数据的统计模型。我们对彩色环志质量的差异进行了补偿，并通过将种群规模、冬季严酷程度以及繁殖成功率等因素作为协变量纳入统计模型，研究它们对存活率和忠诚度的影响。
成年鸬鹚的年存活率逐年波动（0.74 - 0.95），平均为0.88。欧洲的种群规模和冬季温度共同解释了存活率年际变化的52 - 64%。两性之间的存活率差异小于1%。年龄约12岁以上的鸬鹚存活率较低，而两岁的鸬鹚存活率与成年鸬鹚相似。1990年后，对繁殖地的忠诚度从近1降至约0.90，这意味着每年有10%的永久性迁出。这一变化与食物可获得性的下降同时发生。
显然，当种群规模较大时，冬季严酷程度对存活率的影响更为严重。这可能是由于优质越冬栖息地饱和，迫使一些鸟类在条件较差的栖息地越冬，在那里它们更容易受到寒冷冬季的影响。因此，至少在寒冷的冬季，有证据表明成年鸬鹚的存活率存在密度依赖性。
欧洲普通鸬鹚在20世纪70年代和80年代保持的高种群增长率，部分原因可能是未成熟和成年鸟类的存活率异常高，这可能是由于没有狩猎、种群密度低以及食物可获得性高所致。
