The three-part mini-series, bringing a unique insight into the staff and animals at London Zoo, averaged 3.3m (14.1%) on ITV1 from 8pm and 109k (0.5%) on ITV1 HD.
However, the show was eclipsed in the 8pm hour by Holby City, which entertained a healthy 5.96m (25.5%) on BBC One.
Primetime was comfortably dominated by BBC One, after new series Turn Back Time: The High Street had 5.2m (22.5%) from 9pm, outperforming the first part of a screening of Oceans 13, which secured 2.69m (11.6%) on ITV1 and 128k (0.6%) in HD.
After the ITV national and regional news, the second part of the film brought in 1.64m (14.5%) from 10.45pm, beating Film 2010 with Claudia Winkleman, which had 1.29m (9.7%) on BBC One.
Earlier in the evening, The One Show appealed to 4.97m (22.3%) on BBC One from 7pm, while River Monsters had 2.96m (12.7%) on ITV1 from 7.30pm.
Over on Channel 4, Celebrity Coach Trip pulled in 2.14m (13.2%) between 5.30pm and 6pm. Later, the new series of Kirsty's Homemade Home continued to 1.96m (8.4%) in the 8pm hour and 219k (0.9%) an hour later.
The programme was followed by the final of Ramsay's Best Restaurant, which cooked up 1.49m (7.3%) between 9pm and 11pm. A further 162k (0.9%) watched the show on timeshift.
BBC Two's Coast pulled in 1.81m (7.9%) in the 7pm hour, before Alan Titchmarsh's Garden Secrets captivated 1.9m (8.1%). A Money Programme special on BP's $30bn Blowout then educated 1.01m (4.4%) in the 9pm hour.
On Channel Five, Street Market Chefs entertained 451k (1.9%) from 7.30pm. It was followed by Sea Patrol UK, which thrilled 805k (3.5%). CSI: Miami and CSI: NY grabbed respective audiences of 2.04m (8.8%) and 1.43m (7.9%) from 9pm.
BBC One dominated primetime with 24.6% against ITV1's 15.2% (HD: 0.5%). Channel 4 came in third with 6.6% (+1: 0.6%), followed by BBC Two with 6.2% and Channel Five with 5.2%.
Elsewhere, lesbian drama Lip Service continued to 503k (3.7%) on BBC Three between 10.30pm and 11.30pm.
A new episode of The Vampire Diaries grabbed 448k (1.9%) on ITV2 in the 9pm hour, while 89k (0.5%) watched on timeshift.
BARB ratings data supplied by Attentional