No one is ignoring attrition on his army due to attacks on his march from Spain, Gabriel doesn't, only the size of his army, which is something you agree with me on, that it was smaller than what the ancient sources describe.
Hannibal had plenty of pack animals for supplies on his march, it's the attacks on these and their losses that was a major problem and concern during his route through the Alps. Sheen has calculated that for his march from the Pyrenees to the Rhone, he'd have needed many pack animals to meet the armies daily needs:
Daily supply needs of Hannibal's army when consisting of 50,000 infantry and
9,000 cavalry.62
Total Number x Wt. of Ration = Totals
People 80,00063 3 lbs. 240,000
Cavalry horses 9,000 10 lbs. 90,000
Pack-animals 1,600 10 lbs. 16.000
Total 346,000
Total number of pack-animals needed for: One day = 1,821
One week= 18,630
Ten days = 34,600
And around 27,000 for his journey from the Rhone to Italy. Along with his baggage train, of course. These figures assume that it was not necessary for the army to carry water or the additional 10 lbs. of forage each animal required every day. Such a need would only have arisen if the army marched through desert or uncultivated areas... Hannibal usually confined his operations to agricultural regions to meet these daily needs (Sheen, Hannibal's Mules, Historia: Zeitschrift für Alte Geschichte, Vol. 45, No. 2 (2nd Qtr., 1996), pp.173) . Let's ignore Gabriel's flawed claim comparing it's marching length to a World War 1 army, there were clearly long lines of supplies and baggage which was what drew the Celts to attack the army.
Here's Polybius on one such early attack:
When day broke the natives saw what had taken place, and at first desisted from their attempts; but presently the sight of the immense string of beasts of burden, and of the cavalry, slowly and painfully making the ascent, tempted them to attack the advancing line. Accordingly they fell upon it at many points at once; and the Carthaginians sustained severe losses, not so much at the hands of the enemy, as from the dangerous nature of the ground, which proved especially fatal to the horses and beasts of burden. For as the ascent was not only narrow and rough, but flanked also with precipices, at every movement which tended to throw the line into disorder, large numbers of the beasts of burden were hurled down the precipices with their loads on their backs. And what added more than anything else to this sort of confusion were the wounded horses; for, maddened by their wounds, they either turned round and ran into the advancing beasts of burden, or, rushing furiously forward, dashed aside everything that came in their way on the narrow path, and so threw the whole line into disorder. Hannibal saw what was taking place, and knowing that, even if they escaped this attack, they could never survive the loss of all their baggage, he took with him the men who had seized the strongholds during the night and went to the relief of the advancing line. (Polybius, 3,51).
