Ocotillo flowers as food resource for the mule deer during the dry season

Abstract

The plant locally known as ocotillo, Fouquieria splendens (Fouquieriaceae) is a shrub distributed in arid zones of Mexico and southwestern United States. In Mapimi Biosphere Reserve, Durango, it has not leaves for most of the year; these emerge after the first rain. Inflorescences emerge in March, being bright red and lasting only a month. These inflorescences are highly sought after by animals, including insects, birds and the mule deer (Odocoileus hemionus). The objectives of this study were: 1) quantify the inflorescences produced by each plant (during March), 2) estimate inflorescence availability for mule deer, and 3) quantify its contribution in biomass (fresh weight) and nutrient content. This will contribute to understand why deer consume these flowers in the dry season. In March 2012 a field sampling was carried out in the Mapimi Biosphere Reserve, to measure the characteristics of each individual plant, quantify the number of inflorescences produced, the number available for mule deer, and the nutrients they contribute. The nearest-neighbor method was used, measuring 30 ocotillo individuals in nine sites. Inflorescences were collected from different plants to estimate fresh weight and determine nutrient content by proximal chemical analysis. A total of 270 ocotillo plants were sampled. There was a positive correlation between plant diameter and number of both branches and inflorescences. An average of 30 inflorescences was observed, and their availability for deer was 42 % (3,306/7,951) of the total. The average weight of 74 inflorescences collected was 74.8 ± 20.4 g; each plant produced up to 3 kg. These contain high levels of protein (15 % dry basis), carbohydrate (67 %), and 3,085.98 kcal/kg of metabolizable energy; 85 % are digestible nutrients. The mule deer selects plants with high nutritional values that are available in critical seasons such as the dry season. To note, ocotillo flowers emerge when there is food shortage (dry season), and are consumed by deer. A positive correlation was found between number of branches, plant diameter and total number of inflorescences (and its availability). Ocotillo flowers represent an important nutritional resource for deer, because inflorescences have high protein and sugar levels, in addition to having digestible nutrients and that each plant produces around 1.5 kg of inflorescences available for deer in the dry season.