Can a Delegate have an optional parameter?

I have the below code that was working fine until I tried adding the bool NetworkAvailable = true portion. Now I get a Method name expected compile time exception at Line 4 below.

void NetworkStatus_AvailabilityChanged(object sender, NetworkStatusChangedArgs e)
{
   var networkAvailable = e.IsAvailable;
   SetUpdateHUDConnectedMode d = new SetUpdateHUDConnectedMode(UpdateHUDConnectedMode(networkAvailable));
   this.Invoke(d);
}   

delegate void SetUpdateHUDConnectedMode(bool NetworkAvailable = true);
private void UpdateHUDConnectedMode(bool NetworkAvailable = true)
{
   ...
}

I am, admittedly, new to Delegates and Optional Parameters so I would be grateful for any insight. Thanks.