Receive strange symbols in XBee network

I’m running sensor network with base station (which consists of XBee Explorer and XBee Series 2) and two sensor nodes (each one consists of Arduino Mega, Wireless Proto Shield, XBee Series 2 and temperature sensor TMP102). I’m using this code for each node:

#include <Wire.h>
int tmp102Address = 0x48;

void setup(){
  Serial.begin(9600);
  Wire.begin();
}

void loop(){

  float celsius = getTemperature();
  Serial.print("NODE 1");
  Serial.print("\n");
  Serial.print("Celsius: ");
  Serial.println(celsius);

  delay(7000); 
}

float getTemperature(){
  Wire.requestFrom(tmp102Address,2); 

  byte MSB = Wire.read();
  byte LSB = Wire.read();

    int TemperatureSum = ((MSB << 8) | LSB) >> 4; 

  float celsius = TemperatureSum*0.0625;
  return celsius;
}

The serial monitor displays correctly the data from each node when I chose the appropriate serial port. But when I’m using serial monitor for the base station port there are strange received symbols between sensors’ data:

I appreciate any help!