I read the Doug Saunders link. None of the statistics appear to be sourced.
Source: Statistics Netherlands, 2006, as cited in C.F. Westoff and T. Frejka, Population and Development Review 33, no. 4 (2007): table 3.
Fertility Falling in Immigrants' Home Countries
Fertility levels in the countries of origin for Muslim immigrants are reflected in different fertility rates among Muslim groups in Europe, as immigrants often arrive with the norms of their home countries. In Norway, the TFRs varied substantially depending on where women were born. Among immigrant women living in Norway, Somali women had a TFR of 5.2 in 1997-1998, compared with 4.8 for Iraqis, 3.1 for Turks, and 1.9 for Iranians. Native Norwegian women had 1.8 children on average during the period.
But fertility has been falling in many Muslim countries in the Middle East and Africa, which may help explain why younger Muslim women have lower fertility than older women. In Turkey, the TFR dropped from 3.3 in the 1985 to 1990 period to about 2.2 in 2003. Over the same span of years, the TFR fell from 4.5 to 2.5 in Morocco, and from 5.6 to 2.1 in Iran, according to UN estimates.
Muslims who grew up in Europe in immigrant families are also likely to adopt the majority population's preference for smaller families. All countries in Europe have had low fertility for decades.
http://www.prb.org/Publications/Articles/2008/muslimsineurope.aspx