<?xml version="1.0" encoding="UTF-8"?>
<filelist>
   <file>birds2014.xml</file>
   <file>birds2013.xml</file>
</filelist>

<xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
    xmlns:xs="http://www.w3.org/2001/XMLSchema" exclude-result-prefixes="xs" version="2.0">
    <xsl:output omit-xml-declaration="yes" indent="yes"/>
    <xsl:strip-space elements="*"/>

<xsl:template match="*">
        <xsl:apply-templates/>
        <xsl:variable name="files" select="document('filelist.xml')/filelist/file"/>
            <xsl:element name="birdname">
                <xsl:for-each select="document($files)">
                    <xsl:value-of select="//spbird">
                    </xsl:value-of>
                </xsl:for-each>
            </xsl:element>
    </xsl:template>

<birdname>Papagei Wellensittich Pfau</birdname>
<birdname>Papagei Wellensittich Pfau</birdname>
<birdname>Papagei Wellensittich Pfau</birdname>
<birdname>Papagei Wellensittich Pfau</birdname>
<birdname>Papagei Wellensittich Pfau</birdname>
<birdname>Papagei Wellensittich Pfau</birdname>
<birdname>Papagei Wellensittich Pfau</birdname>
<birdname>Papagei Wellensittich Pfau</birdname>
<birdname>Papagei Wellensittich Pfau</birdname>

<birdname>Papagei</birdname>
<birdname>Wellensittich</birdname>
<birdname>Pfau</birdname>

<xsl:template match="*">

<xsl:template match="/">

<birdname>Papagei Wellensittich</birdname>
<birdname>Pfau</birdname>

<xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
    xmlns:xs="http://www.w3.org/2001/XMLSchema" exclude-result-prefixes="xs" version="2.0">
    <xsl:output omit-xml-declaration="yes" indent="yes"/>
    <xsl:strip-space elements="*"/>

<xsl:template match="*">
        <xsl:apply-templates/>
        <xsl:variable name="files" select="document('filelist.xml')/filelist/file"/>

                <xsl:for-each select="document($files)">
                       <birdname>
                         <xsl:value-of select="//spbird">
                       </birdname>
                    </xsl:value-of>
                </xsl:for-each>
            </xsl:element>
    </xsl:template>

<xsl:for-each select="document($files)">
    <birdname>
        <xsl:value-of select="//spbird"/>
    </birdname>
</xsl:for-each>

<xsl:for-each select="document($files)//spbird">
    <birdname>
        <xsl:value-of select="."/>
    </birdname>
</xsl:for-each>