In the Netherlands, breeding populations of wader meadow birds are in sharp decline. One possible cause is that breeding areas are becoming less open because of tall trees and other factors. The effects of tree lines are generally studied by means of transversal studies spanning a short period of time. We report on a longitudinal field study from 1993 to 2010 into the breeding densities of Eurasian Oystercatcher (Haematopus ostralegus), Northern Lapwing (Vanellus vanellus), Black-tailed Godwit (Limosa limosa) and Common Redshank (Tringa totanus) in the Demmerik polder, the Netherlands. One part of this polder, a nature reserve, has an older tree line, while two agricultural parts are divided by a newly developing tree line. As the tree line in the agricultural parts was developing, foraging families of Greylag Goose (Anser anser) showed a strong increase in only one of these parts during the breeding season. During the same period, the density of avian predators also increased in the whole polder. Analysis shows waders avoid trees in both situations: with an existing tree line (a static situation) and with a growing tree line (a dynamic situation). We investigated the possible role of geese and avian predators in explaining the decline in density of breeding wader meadow birds, by systematic comparison of several different models. In these models, the effect of the growing tree line has the greatest impact on breeding meadow birds. Models with geese describe the trends of breeding wader meadow birds better than those including avian predators, but since these two variables, geese and avian predators, are confounded, no definitive conclusion can yet be drawn. Potential explanations of and functional mechanisms behind the strong decline in breeding meadow bird populations in this area are discussed.

中文翻译：

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纵向研究树木，鹅和鸟类捕食者对涉禽草甸鸟类繁殖的影响：以荷兰Demmerik polder为例

在荷兰，涉水草甸鸟类的繁殖种群急剧减少。一个可能的原因是，由于高大的树木和其他因素，繁殖区的开放程度降低了。通常通过在短时间内进行横向研究来研究林木线的影响。我们从1993年至2010年的纵向田间研究报告了欧亚蛎cat（Haematopus ostralegus），北田wing（Vanellus vanellus），黑尾God（Limosa limosa）和红Red（Tringa totanus）的繁殖密度在荷兰的Demmerik pol田。该田的一部分（自然保护区）具有较旧的林木，而两个农业部分被新近形成的林木划分。随着农业地区林木的发展，对灰雁（Anser anser）的家庭进行觅食在繁殖季节仅这些部分之一表现出强劲的增长。在同一时期，整个田中鸟类捕食者的密度也增加了。分析表明，涉水者在两种情况下都避开树木：既有树线（静态）又有树线增长（动态）。通过对几种不同模型的系统比较，我们调查了鹅和鸟类捕食者在解释繁殖涉水草甸鸟类密度下降中的可能作用。在这些模型中，林木生长的影响对草地鸟类的繁殖影响最大。鹅的模型比涉禽的更好地描述了涉禽草甸鸟类的繁殖趋势，但是由于鹅和鸟类的捕食者这两个变量是混杂的，因此无法得出明确的结论。